CROWN - Croatian World Network -
Professor Mladen Vranić, outstanding Croatian scientist in Canada
By Prof.Dr. Darko Zubrinic
Published on 01/31/2008
Distinguished researcher and educator in medical sciences (endocrinology and metabolism) and former chair of physiology, where 85 years ago insulin was discovered. He earned the title of Honorary Medical Doctor from Karolinska Institute, Sweden. He is a Fellow of the Royal Society of Canada, and a corresponding member of the Croatian Academy of Sciences and Arts.

Distinguished specialist in endocrinology and metabolism

Cycling from Scilla to Charybdis: The Unsteady Odyssey of Metabolic Regulation

Biography of Mladen Vranic, MD, DSc, FRCPC, FRSC

Professor of Physiology and Medicine, Faculty of Medicine, University of Toronto

By: Richard Bergman, University of South California, School of Medicine, Los Angeles, USA



Professor Mladen Vranić is distinguished researcher and educator in medical sciences (endocrinology and metabolism) and former chair of physiology, where 85 years ago insulin was discovered. He earned the title of Honorary Medical Doctor Institute, Sweden. He is a Fellow of the Royal Society of Canada, and a corresponding member of the Croatian Academy of Sciences and Arts. He is the only Canadian who got most prestigious awards from American Diabetes association, and 2007 inaugural life achievement award from Canadian Diabetes association.


Mladen Vranic was born in Zagreb in 1930 to Vladimir and Ana, and grew up an only child in an environment strongly influenced by the academic pursuits of his father, who was a mathematician. At different times his father held positions as Professor and Dean in the Faculties of Economics, and Engineering, and in addition lectured on the theory of probability in the Faculty of Science. The Vranic home was a gathering place, not only for colleagues from the Sciences but also from the Arts, including actors from the theatre. It was a wonderful experience for a young person and unique to the culture of Zagreb at the time. Unusual high school experiences were helpful in preparing Vranic' scientific career by forging those aspects of his character that reflected stubbornness, intensity but flexibility. His first year of high school coincided with the German occupation of Jugoslavia, and the fascist Ustase government in Croatia. Mladen's immediate family escaped in 1941 to Crikvenica, which was under Italian occupation. Sadly, however, most of his relatives were killed in the extermination camps of the Ustase or the Nazis. The following year was spent in Italian concentration camps at Kraljevica and Rab, respectively. Interestingly, some of the teachers in these concentration camps became University Professors in Zagreb after the war. Following the collapse of Mussolini's government in Italy in 1943, and because a large part of Croatia was liberated by the Partisans, the family escaped in January 1944 from the island of Rab to Taranto (Italy), which at that time was occupied by the Allied forces. For the last year of the war, his father returned to Croatia to join the Partisan movement, while Mladen, his mother and grandmother stayed in Taranto until the end of the war. These next two years of high school in Taranto were very classical in nature and greatly stimulated a love for literature that Mladen has retained to this day. The circle was complete when he returned to Zagreb for the final three years of high school.

Mladen enrolled into Medical School in Zagreb, where the Department of Physiology had a keen scientific interest in carbohydrate metabolism and diabetes, initiated by Professor Allegretti a few years earlier. This early summer scientific experience in Zagreb was further enhanced by two summer research programmes at the Universities of Vienna and Amsterdam. The only experience Mladen had as a practicing physician was during internship and one year of military service, and since it would have been very difficult to combine clinical practice with basic research he therefore decided to embark on a career as a physiologist. During summers and later, as a research assistant, a close collaboration developed with Drs. Allegretti, Pokrajac, Rabadija and Mihic. The intense teaching of general physiology provided the background for the rest of his career and was a critical early experience for subsequent teaching in the Department of Physiology in Toronto. In medical school, he developed a very close friendship with Dr. Darko Ivancevic (former Head of Nuclear Medicine) and also his family. This friendship and accompanying lengthy discussions on science and many other subjects greatly enriched his life. Since the time that Mladen no longer had relatives in Zagreb, he has felt that this was his Zagreb family.

His Ph.D. thesis reported on his work stimulating the growth of pancreatic islets by cortisol in guinea pigs, providing early evidence that new islet cells sprout from ducts. Clearly, acinar cells were not necessary because hypertrophy of islets could be produced even when all acinar cells were destroyed by ligation of the pancreatic duct. This work was published in Diabetes, his first publication in a top international journal (1). Although he did not pursue this topic further, growth of islets from ductal cells is now being studied with great vigour using modern methodology, since it is a very important topic for the understanding of the life cycle of islet cells in physiology and diabetes. This area of research has become very sophisticated in the last 10 years and Mladen has recently begun a programme about the contrasting effects of exercise training and chronic stress on the dynamics of pancreatic islets and their relationship to the hypothalamic-pituitary-adrenal axis. This could then close the circle of the work begun in Zagreb.

Mladen discussed his work with colleagues at a number of universities in West Germany, but the visit that was to shape his future was with Professor Werner Creutzfeldt, whose father co-discovered Creutzfeldt-Jacob Disease many years earlier. Because he was interested in obtaining a post-doctoral fellowship in the United States, it was suggested that Dr. Creutzfeldt introduce him to Dr. Albert Renold during the next International Diabetes Federation meeting, which was to be held in Geneva. The number of participants at these early meetings was far below that of the present day, so that it was possible for all the participants to undertake a pleasure trip on the lake. As promised, Mladen was introduced to Albert Renold who told him that he would love to accept him at Harvard, but he had just agreed to return to his hometown of Geneva. Nevertheless, he was still to play an important role in Mladen's scientific endeavours after he joined him much later for a sabbatical leave in Geneva.

Following Mladen's initial disappointment, Dr. Creutzfeldt introduced him to Professors Otto and Anka Sirek from the University of Toronto, Canada. Initially, they were very encouraging, indicating that Professor Charles H. Best was very interested in young people and that he would certainly wish to meet with him and hear his presentation at the meeting. Unfortunately, a meeting was not possible and no post-doctoral positions were available. Despite this additional setback, he continued to correspond with the Sireks and to his greatest delight, after many months received an invitation from Professor Best to come to Toronto in January 1963 as a post-doctoral fellow.  He was very excited at the prospect since Professor Best, a co-discoverer of insulin, was one of the best-known physiologists of the time, and he began to make preparations for his departure.

The Ministry of the Interior of Croatia agreed to give him a passport, but his wife Magda and 2-year old daughter Iva would have to remain behind. He declined. Finally, fate intervened in the form of Mrs. Savka Dabcevic, who had been a student of his father's in economics and a patron of his mother's beauty salon. Mrs. Dabcevic was a Member of Parliament in 1962 and became President of the Croatian government in 1967. He was extremely grateful for her support. Although initially there was resentment against Croatians who settled in another country, when they met in Toronto a few years ago, he was gratified by the pride she expressed in his achievements. Upon arriving at Montreal Airport, he was interviewed by Immigration Officers and was quite tense when one officer asked him for very specific details of his plans to work with Dr. Best. He was convinced that the information was for the Secret Police and avoided giving any answers. It turned out that this was actually a doctor who was supposed to be conducting a medical examination, but was actually more interested in hearing about his proposed research with Dr. Best.

Three years after their arrival in Canada Mladen and his family returned to Zagreb for a visit. It was an incredibly emotional moment for him and for their parents. He realized how, when living in Croatia, he had taken for granted the beauty of its cities, the Dalmatian Coast and the mountains. On each subsequent visit, he rediscovered some new aspects of Zagreb. His special love is for the incomparable old city. He remembers one poignant incident when he and his father took the lift to the top of Krvavec in the Slovenian Alps. When they told the Hotel Director that they planned to go for a hike, he looked at his father's shoes and exclaimed, “You cannot possibly hike the Alps in these shoes!” He promptly took off his own shoes and made a temporary exchange with Mladen's father. Both were very moved by this warm and generous act. Mladen occasionally felt resentment from some people that he had left Croatia, but he knew that contact with emigrants was not always looked at favorably by the government in power. One exception was Dr. Ivo Padovan, who is now President of the Croatian Academy of Arts & Sciences. In 1967 he stayed with the Vranics while attending a meeting of Otolaryngologists in Toronto. Mladen still remembers his very impressive lecture, and how he greatly strengthened the collaboration in his specialty between the Universities of Zagreb and Toronto. He also encouraged Mladen by taking an interest in his work, which at that time was in its initial stages. They had a great dinner together with Charlie Best and his wife, Margaret and since that time, Ivo and he have remained close friends. Mladen is especially grateful for Padovan's help when his mother was severely ill.

Mladen also developed a close relationship with Zdenko Skrabalo. As mentioned, they collaborated scientifically and he attended many meetings that Zdenko organized. What was especially impressive was the great care with which these meetings were organized, the high quality and especially the warm atmosphere. On one occasion, all members of the Symposium were driving early in the morning on a bus from Dubrovnik along the Dalmatian Coast when they were served freshly dried figs and Grappa. Even more memorable, however, were the splendid dinners prepared by Zdenko's wife, Lidija, in their home. Zdenko not only had a great knowledge of diabetology, but a wide encyclopedic knowledge that was appreciated by all. Under his leadership, the Croatian model of diabetes treatment was initiated and received international recognition. Part of the model was the establishment of a network of treatment centers around the country providing excellent, integrated diabetes care. Zdenko realized that the mobility of scientists was an essential phenomenon that had always existed, and that a close collaboration between his Institute and Mladen's could be of considerable mutual interest. This collaboration also included Suad Efendic. In 1984 the Diabetes Centre of the University of Toronto invited Zdenko to present a lecture on “Diabetes in the Third World”. Prior to the lecture Mladen and Zdenko had attended a meeting together in Washington, and at the airport they suddenly realized to their horror that Zdenko did not have a Canadian visa. The two of them rushed to the Canadian Embassy with very little hope, because the visa needed to be issued instantaneously in order to catch a plane in time for Zdenko to deliver his lecture in Toronto. Fortunately, he had with him the University of Toronto Newspaper, which advertised all the lectures for the week. He showed it to the Canadian official who noticed that above the name of Skrabalo, was the lecture of Dr. Henry Kissinger. He got the visa!


When Mladen met Dr. Best for the first time in Toronto he was very apprehensive. He was even more nervous when he was asked to present a seminar of his work from Zagreb, since he had overheard Dr. Sirek asking Dr. Best what were his first impressions:- “Well,” Best responded, “his English is pretty good but otherwise I don't know.”  Following Mladen's presentation, Dr. Best was most enthusiastic - one of the most important encouragement for his future work. Dr. Best was always available for discussions and appointments could be made at short notice. Best played an important role in attracting graduate students, post-doctoral fellows and visiting scientists to the Department of Physiology in the University of Toronto, and it is due to him that Toronto has continued to be a Mecca for diabetes research since the discovery of insulin in 1921 (2). For a while he was in charge of endocrinology teaching to Medical Students. He would introduce Dr. Best for his lecture, “The Discovery of Insulin” and when the class was over, all 250 students would line up to obtain his autograph. Quite an impressive sight!  He retired as Chairman of the Department in 1965 and Dr. Haist took over.

During his two post-doctoral years he worked with Drs. Wrenshall and Rapaport. Dr. Wrenshall, both a physicist and physiologist by training, was a pioneer in tracer methodology, which allowed measurement of fluxes of metabolites in vivo quantitatively. Rapaport was a surgeon who came from Romania and at the time was a pioneer of experimental surgery. He did ground breaking research on liver structure and function. His main achievement is known today as “Rapaport's liver acinus”. When he arrived in Toronto after WWII, he began work in experimental surgery and diabetes with Dr. Markoviz. It was rumoured that Dr. Markoviz might have been the famous Canadian medical doctor described in the movie, “Bridge Over the River Kwai”. This work fueled his interest in establishing the first insulin clamp. They removed two-thirds of the pancreas, while the remaining one-third was grafted under the skin of the dog.  This graft had its blood supply through a peduncle and was enclosed in a plastic casing.  A catheter was introduced simultaneously into the portal vein. At the time of the experiment the graft was removed from the casing and clamping of the peduncle induced instantaneous diabetes while the removal of the clamp restored normal insulin secretion into the portal vein. Most importantly, if the peduncle was cut and exogenous insulin infusion started into the portal vein, then the insulin clamp would be established in a dog that had never been diabetic. On the basis of those experiments he measured for the first time ever, the rate of basal insulin secretion in dogs. He was very enthusiastic when the same value was later reported in man. This preparation also allowed him to investigate the effects of hormones and metabolites independently of insulin secretion. For the first time he demonstrated what is now called “glucose effectiveness”. This means that during glucose tolerance tests, a substantial amount of glucose is removed by the tissues in an insulin-independent process. Insulin release made this removal more efficient but basal insulin secretion sufficed to return glucose to normal after a glucose load. Mladen was very eager to continue with this line of research but he was concerned that it might be difficult to establish this upon his return to Zagreb. Consequently, he thought that the best route would be to try to prolong his stay in Toronto.           

Before the Chairman of the Department of Physiology would offer Mladen an academic appointment, he wanted to know that he was competitive enough to be offered a position in the United States. It was suggested that he visit a number of research institutes in the U.S., and to facilitate this a young graduate student in the Department named John Cowan (now President of the Royal Canadian Military College in Kingston, Canada) was enlisted to fly a four-seater Cessna plane from Toronto to Minneapolis, Washington, St. Louis and New York. He was an excellent, local pilot but what Mladen was not told was that this was his very first flying expedition outside of the Toronto area. Mladen's first test was to see whether or not he could endure a few acrobatics - he passed with “flying colours”. It must have made quite an impression at the places they visited, since it was quite puzzling to people how a foreign post-doctoral fellow could afford to engage a plane and a pilot. There were no problems navigating, but while flying around the Empire State Building, John became very annoyed at Mladen's handling of the video camera. When he realized that they might lose control of the plane Mladen decided from then on to follow all of John's instructions with the utmost care. In one incident, the arrangements were so comfortable in the back of the plane and Mladen was so relaxed, that he thought he would read the newspaper - in mid flight, with the cockpit cover open. In an instant, the papers were atomized and it took John years to remove all the bits and pieces from his plane. The most critical outcome of the trip was the offer of an Assistant Professorship in the laboratory of Dr. Rachmiel Levine, one of the great names in the field of diabetes. His book on glucose homeostasis was legendary at the time. Upon Mladen's return to Toronto the news was spread that he was wanted in the U.S. and as a result he was offered a position as Assistant Professor in the Department of Physiology at the University of Toronto. Today, academic appointments and granting of tenure are extremely elaborate procedures with mountains of paperwork. At that time, months after both his appointment and granting of tenure, Dr. Haist remarked that the Department had never received either his M.D. or Ph.D. diplomas. One can only yearn for those times of relaxed trust!

At that time it seemed impossible to become a Landed Immigrant in Canada. It so happened, however, that Mladen's car was insured by a company that once belonged to the Minister of Finance of Canada before he entered politics.  The secretary of the insurance company told him that she would write to her former boss to see whether he could help with visas for Mladen and his family. Indeed, he still has the extensive correspondence between the Minister of Finance and the Minister of Immigration - an exchange lasting over 2 years. One day, a Royal Canadian Mounted Police Officer arrived unexpectedly at the door to interview him at great length. Mladen asked whether he also needed to speak to his wife, to which the officer replied, “There is no need.” This was long before the feminist movement swept over the North American continent. There was a second, later visit from the same officer asking the same questions. The accuracy of repeated answers was the test of honesty. At that time, Mladen's memory was better than today, and he was granted the visa. The special benefit was that the secretary of the Insurance Company invited the family to one of the greatest dinners they had ever tasted, reminding him of the fabulous dinner described in Gogol's Dead Souls, especially the generous amount of ice cold vodka that accompanied it.

Life in a new country posed many and varied challenges. His first daughter was 2 1/2 years old and fluent in Croatian. On one visit to relatives in Montreal, she was so frustrated that nobody understood her, she gave endless speeches, in Croatian, to a beautiful German Shepherd dog who showed great understanding. Mladen's wife faced a long period of 7 years to qualify as M.D. and to write the Canadian specialty exams in Physical Medicine and Rehabilitation. In 1971, a particularly emotional and dramatic period devastated Mladen's family. While visiting in Toronto, his mother suffered a massive heart attack on the day that she was due to return to Zagreb. She spent many weeks in the hospital, during which time her own mother, Mladen's grandmother, died in Zagreb. To everyone's amazement, the shock of this news normalized his mother's heart rhythm. During her convalescence, however, Mladen's father was hospitalized in Zagreb with a bleeding ulcer. Immediately following this, Mladen's second daughter, Maja, died of leukemia at the age of 11 months. It was a time of terrible grief.

His work in the field of diabetes has been recognized by a number of awards, including the inaugural Banting & Best Memorial Lecture at the 12th Congress of the International Diabetes Federation in Madrid, Spain (1985). This lectureship was particularly important to him because his work in Canada was initiated by Dr. Best. For Mladen, the most important recognition of his work came when he was awarded the American Diabetes Association's Banting Medal and Lectureship for Distinguished Scientific Achievement. This award was established 60 years ago, following the death of Banting, and one award is given annually. It is generally considered to be the most important international recognition for original research in Diabetes and to date, he is the only researcher working in Canada to have received it. Six weeks before the lecture was scheduled to be given in Washington, D.C., he was riding home from work on his bicycle when he had a collision with a good-looking woman (at least that's how he remembers it), who was also riding her bicycle. The following day, while attending a scientific meeting at Sunnybrook Hospital in Toronto, he suffered a stroke. Luckily, he was immediately whisked into emergency and taken care of. There were two interesting episodes related to the incident. When he began to talk, it was in Croatian and not English. His English wife was very concerned that she would now have to start taking Croatian lessons. When the neurologist came to examine him, he informed his wife that because Mladen could not answer any of the very basic questions that were posed, the prognosis did not look good. It turned out that the neurologist had asked him, in English, about words he had never known in the first place. The test was repeated using questions from the scientific jargon and the diagnosis became excellent. Indeed, after two weeks in hospital he was able to prepare his Banting lecture and then deliver it – with 5,000 people in the audience. After the lecture, he held a reception for many friends, including a sizable group of diabetologists from “Vuk Vrhovac” and Ljubljana. It was on this day that his friends from Ljubljana learned with horror that the Yugoslav army had attacked Slovenia.

Sabbatical at the University of Geneva, Switzerland:     As indicated earlier, initial plans to work at Harvard with Albert Renold failed to materialize when Renold became Head of the Institute of Clinical Biochemistry in Geneva. Albert persuaded Mladen, in his inimitable and special way, to spend a year (1976/77) at that unique institution. Albert, who was also Vice President of the University, had made provisions for a special fund for post-doctoral fellowships that was created from salaries of deceased or retired professors (again reminiscent of Gogol). Such funds could be used until replacement appointments were made - a very slow process in Switzerland. The laboratory was housed in a beautiful villa surrounded by flowers and trees. The ideal setting, combined with the presence of Albert attracted a large number of students, fellows and sabbatical professors from all over Europe and North America. Mladen felt as if he had been permanently adopted into a large extended family of diabetologists, all related by virtue of association with Albert and his charming wife, Jacqueline. Together, they provided a support system, which included very generous hospitality in their home - quite unique in Switzerland. One recollection, for example, was an occasion when the lights went out in their apartment and Jacqueline arrived within 15 minutes with a large toolbox to replace the fuse. Albert was fluent in English, French and Italian and it was in part due to his efforts that Diabetes meetings in Europe were held in English, and that Diabetologia and the European Journal of Clinical Investigation were established and also used English exclusively. The University of Geneva had a villa in the Engadines and for two weeks during the Christmas holidays, a number of professors with their families spent time together in a region loved by Nietsche and Giacometti. It is a real paradise for skiers.

Mladen's scientific interests were flourishing. He established the biological effects and control of release of extrapancreatic glucagon and the kinetics of tritiated insulin during exercise as described above. It must have been very stimulating to discuss clinical and basic problems endlessly with scientists like Steve Fajans, Joe Larner and Phil Gorden (former head of NIDDK, Bethesda). A short visit to the Institute from Ed Horton (former Chair of the Department of Medicine at the University of Vermont and currently Professor at Harvard University) initiated a lifelong and very close friendship with Ed and his family.

Geneva was strategically located, giving him an opportunity to visit a large number of European universities. While there, a meeting was organized in Cambridge, England for all Faculty Scholars of the Josiah Macy Foundation. It was a very intimidating experience for him to give a lecture just ahead of Dr. Sanger, who had been awarded the Nobel Prize for the discovery of the structure of insulin. Sanger lectured on the sequence of nucleotides of DNA, which at that time was over 90% complete, and this work later resulted in his second Nobel Prize. Only Sanger and Marie Curie were awarded two Nobel Prizes for science. One of the exciting events was when Dr. Skrabalo invited Albert, Lelio Orci and myself to give the inaugural Vuk Vrhovac Memorial Lectures to commemorate the 50th anniversary of the foundation of the Institute for Diabetes in Zagreb. Vuk Vrhovac was an endocrinologist who visited Toronto soon after the discovery of insulin and realized the importance of dedicating a special institute to this disease. In ensuing years, due to Zdenko and later to Mate Granic and Zeljko Metelko, this became a leading Diabetes Institute.

A sad event during his stay in Geneva was the illness and subsequent death of his father. He was a diabetic and eventually, his diabetes accellerated a generalized atherosclerotic disease. Mladen remained close to his side during the last week of his life, during which time he thanked him for restoring his belief in life. The same night he died. Dr. Devidee, a mathematician and friend, delivered a beautiful speech to a large audience, highlighting Mladen's father's accomplishments and contributions. One fact that Mladen found most remarkable was that his father was responsible for bringing the first computer to Zagreb University, which apparently never worked properly. His father was always trying to convince the other, more theoretical mathematicians, that the computer era had begun. Their reluctance stemmed in part from the fear that computers would interfere with the purity of mathematical thinking. He was very well known as a superb lecturer with a strong sense of humour. An oft-quoted example is when, during an examination, he would urge a student to quickly open the windows, so that all of the stupidities that he uttered could be removed from the room. Unfortunately, this type of humour is no longer politically correct, particularly in North America.

Collaboration  with the Department of Endocrinology, Karolinska Institute, Stockholm:

Drs. Suad Efendic and Rolf Luft were keen to introduce tracer methods into their studies of the pathogenesis and pathophysiology of diabetes. Mladen was in Stockholm for over a week but did not see the city at all, as he was literally held hostage in their laboratory. Suad was an old friend who had been a student of medicine in Zagreb when Mladen gave seminars to medical students. He always tells Mladen that his seminars persuaded him to choose science as a career. Thus, Mladen jokingly counts Suad as his first student. For many years, Rolf was either a member or Chair of the Nobel Committee for Medicine and Physiology. He spent 30% of his time every year studying the work of the candidates, and thus was one of the most knowledgeable experts in a large spectrum of medical research. He did important early work in different fields of endocrinology. Mladen was very impressed that Rolf always prepared himself for meetings, something he realized when he saw a stack of his papers in front of him, passages variously underlined, as they prepared to discuss some issues. The collaboration with Suad is now in its 25th year and it has been most productive and enjoyable. Clinical investigations were carried out in Stockholm and animal work in Toronto. Suad is former Chair of the large Department of Molecular Medicine in Stockholm, a member of the Nobel Assembly, the Swedish National Academy of Sciences, and corresponding member of the Croatian Academy of Arts and Science.

Ingmar Bergman's movie, Wild Strawberries, describes the incredible pageantry of awarding honorary degrees at Swedish Universities. Mladen would not have believed that one day he would become part of it. Every year, the Karolinska Institute awards one honorary medical degree to a foreigner, and in 1992, following his nomination by Suad and Rolf, he had the great honour to be chosen. At the ceremony itself, the candidate stands before the Dean while he holds a black, top hat above the head. A signal is then given to an official waiting outside who fires a canon, whereupon the Dean lowers the hat. During the ceremony, degrees are also awarded to graduate students and to professors from Swedish Universities. Hundreds of attendees are dressed in identical formal tailcoats or glittering evening dress. For Mladen, this evening represented the culmination of his collaborative work with Suad, and of his close relationship to the Karolinska Institute. This closeness was further emphasized by his appointment as an Adjunct Professor at the Karolinska. It was on Suad's initiative that a series of Toronto/Stockholm Symposia were begun and held every 3 years.

In 1982, 10 years after being diagnosed with breast cancer, Mladen's wife died. There were meetings in Israel and Kenya later the same year and it was fortuitous that Suad was also participating. At that crucial time in his life, Suad was a great comfort to him, never letting him out of his sight. In addition, to divert his mind from the sorrow, he tried to stimulate him to plan experiments that they would conduct together.

The following year, he became Associate Editor of the American Journal of Physiology, possibly the first non-American in this position. In his early days as a physiologist, he considered a publication in this Journal to be the greatest achievement. Now, he was in the position of making decisions affecting publications of other researchers. He already had some experience, previously serving as Associate Editor of the Canadian Journal of Physiology and Pharmacology and of Metabolism.

Mladen began to play tennis with his Editorial Assistant, Linda, whom he had hired when he took the Associate Editor's position with the American Journal of Physiology. Surprisingly, for anyone who knows how Mladen plays tennis, he won every single game. After Linda and he married and she started to unpack her suitcases, he noticed that the luggage contained various Tennis Championship trophies. Tennis has played a crucial role in their life together. During their sabbatical leave in Oxford, when their daughter Claire was 1 1/2 years old, they were scheduled to play doubles with Gerry and Ann Burrow. Gerry was Chairman of the Department of Medicine at the U. of T. and also on sabbatical leave. He was a first-class tennis player and had defeated Mladen on previous occasions. Mladen told Linda that if they won this match, she could have anything she wanted. After thoroughly defeated them by a score of 6-0, Linda informed him that what she really wanted was another child. Thus, his fourth daughter Anne was born. There were no further opportunities to play with the Burrows, since he became Dean of Medicine and Chancellor at the University of California in San Diego, and then Dean of Medicine at Yale University. This is probably fortunate, because otherwise who knows how big their family would be.

Sabbatical at Oxford University, England: In 1986 an exciting opportunity arose for Mladen to study bioenergetic changes during contraction and recovery in diabetic rat skeletal muscle in Oxford, England. He was invited as a Visiting Research Fellow at Merton College, and with his appointment came a newly renovated 14th century house in the heart of Oxford. The only problem was that there was a very low beam dividing the living room from the dining room. Almost daily, he managed to bang his head as he raced from one room to the other. Sometimes, it actually knocked him to the floor. It hopefully had the desired effect of waking him to face the unexpected challenges of life in Oxford - a fate not unlike that of the mathematicians in Gulliver's Travels. One privilege he had was that of eating with scholars from all fields within the College - and it was free! The dinners were very ceremonial, beginning with port in the Queen's Room (wife of Charles I). This was followed by a multi-course dinner at High Table. Nuts and sweets were served in the next room. They were ritually circulated around the common table so that all could partake. One had to choose seats wisely, however, because once they appeared in front of the very eminent Professor of Roman Law, they would remain there for the duration of the evening. It is said that the sweet wine served had come from the same French vineyards for the last 500 years. The evening would generally finish in the coffee room, where hard liquor was served. Mladen probably wouldn't have survived had he joined in this dinner every evening. One rather odd rule was that one was not allowed to invite one's own wife for these dinners, although he could bring anyone else. He also learned upon arrival that Visiting Fellows could request a Master Key that could open all the doors of the College. Now, Merton College has a vast collection of fine art, old silver and priceless books and Mladen naively thought that he could actually exercise this privilege. He described the horror that he saw in the eyes of the Bursar, who politely informed him that this was really not very practical and would be an absolute catastrophe if he were to lose it! The sad event during their sabbatical stay in Oxford was the serious illness and death of his mother. Mladen has always been very grateful for the wonderful care that she received in the Diabetes Centre in Zagreb.

All previous Chairmen of the Department of Biochemistry in Oxford, where he was working, were Nobel Prize winners. The Department reflected an incredible contrast of facilities. On the one hand, it probably had the greatest concentration of Nuclear Magnetic Resonance equipment in the world, while at the same time there were no pencil sharpeners and an open, antiquated lift elevator called “pater noster”, for the reason that one felt a great need to pray upon entering it.

Another highlight of the Oxford sabbatical was an invitation for a private lunch in the home of the late Professor Sir Isaiah Berlin, one of the greatest liberal intellects of this century. He was the stepfather of Philippe Halban, with whom Mladen had worked during his sabbatical leave in Geneva. The atmosphere was congenial and Sir Isaiah had an extremely warm and inquisitive personality. His most famous and widely read essay is entitled “The Hedgehog and the Fox” from the Greek poet Archilochus, who said, “The fox knows many things, but the hedgehog knows one big thing”. Berlin described Tolstoy as a fox who believed himself to be a hedgehog. Mladen refers to it often in his lectures as a metaphor for metabolic and molecular research. In metabolic research, one deals with control systems, regulation, models and a variety of hormones, metabolites and other factors that continuously interplay to maintain our body near homeostasis. It is a continuous fight between certainty and uncertainty and the models are modified as new discoveries are made. The molecular biologist is more focused and better equipped but has more difficulty in integrating his new findings into complexities of the living body. Physiologists today try to integrate the physiology of organs and tissues with molecular approaches that define the function of the cell. Thus, as with Tolstoy, in the biological sciences it is sometimes difficult to make a clear distinction between the fox and the hedgehog.

Professor Mladen Vranić is recipient of the Albert Renold Award

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Collaboration with the University of Zagreb

Collaboration with the University of Zagreb: In 1987 the Faculty of Medicine at the University of Zagreb decided to appoint as Visiting Professors, a number of academics living abroad. The procedure was the same as for regular professors. The first two appointments made were those of Suad Efendic and Mladen. It was for him an important and emotional recognition, which occurred through the efforts of Drs. Skrabalo and Granic, 24 years after his leaving Zagreb. At that time, Mate Granic was emerging as the most promising young diabetologist in Croatia. He was invited to lecture in Toronto and it was a great occasion to have his entire family staying with the Vranics. Mladen wanted to show his wife what real Dalmatian cooking was, and so Mate agreed to barbeque a red snapper. They were duly sent to the fish market with precise instructions as to the size and weight of the snapper. Mate prepared it with great precision, care and perfection. These were his characteristics as a diabetologist and they remained with him as Dean of Medicine and later in his political career as Minister of Foreign Affairs, an incredibly difficult task during and following the war of aggression in Croatia.

In 1989 he decided to hold the first of what was to be a series of Symposia jointly organized by the University of Zagreb (Skrabalo and Granic), the University of Toronto (Vranic and Hollenberg) and the Karolinska Institute, Stockholm (Efendic and Luft). The meeting in Dubrovnik was very successful and attracted many European diabetologists, including the first large Russian contingent. The main organizer of this meeting was Mate, and it was arranged that the Organizing Committee with some guests would visit the University of Zagreb Medical Faculty, the Institute of Diabetes and the President of Croatia. They also visited Dr. Separovic, then President of the University, who depicted a gloomy picture of the impending future. An emotional event for Mladen was just prior to the meeting when he hiked Triglav with Slovenian friends acting as guides. It was his first hike to Triglav since leaving Croatia and he cannot imagine anything more beautiful than looking down at the clouds from high on the rock face. The war, which began two years later, interrupted further organization of this Symposium.

The establishment of the Republic of Croatia gave rise to a number of new initiatives among Croatian immigrants. Mladen served for several years on the Executive of the Almae Matris Croaticae Alumni. Through this group he organized numerous visits and lectureships for Faculty from the University of Zagreb to the University of Toronto. He was appointed Honorary Member, with M. Grmek and Z. Skrabalo, to the Advisory Board of the World Organization of Croatian Physicians and also served as a member of the Advisory Board of the Croatian Medical Journal. During the war he widely circulated information concerning events in Croatia to raise awareness here in Canada. Most of the information was regularly faxed to him from Professor Skrabalo and the Diabetes Centre. During the war Mate Granic (then Foreign Minister of Croatia) visited Toronto and in his speech promised that the integrity of Croatia would be regained despite the awful situation in which a large part of Croatia was occupied by the Yugoslav army.  What Mladen considered to be an optimistic dream of Mate was accomplished. It is one thing that he learned about Mate - his carefully thought out predictions are eventually accomplished.

In the last few years Mladen has been a member of the International Advisory Board of the Medical Studies in English, at the University of Zagreb, Croatia. It is a very important endeavor at the school of medicine, and it is directed by the Dean Mrs. N. Cikes and professor D. Jezek. Mladen is involved in the teaching program on a yearly basis. The University of Zagreb and the University of Toronto signed a memorandum of agreement which should boost cooperation between the two universities. Mladen helped establish such an agreement. He also participated at the first congress of Croatian scientists from Croatia and Diaspora held in Vukovar, November 15 - 19, 2004. It was the first meeting of this sort which promoted the collaboration between the scientists.

Chair of the Department of Physiology, University of Toronto: At the time of his stroke, Mladen was one of the candidates for Chair of the Department. Following his recovery, his physician sent a letter to the Dean indicating that he could still be a viable candidate. He was elected to start as Chair in October 1991. His concern was how he would be able to combine the administration of a very large department with research, publications and extensive travel. Before this appointment he had a variety of administrative functions in the Medical School, Department, Banting & Best Diabetes Centre and as Director of the Best Foundation. Those responsibilities, however, were not comparable to the task of the Chairmanship. He was very lucky that with the tremendous help of his two post-doctoral fellows, Drs. Adria Giacca and Qing Shi, and experienced technicians and students, the lab continued to run smoothly. Soon after his appointment, there was a crisis in the Faculty of Medicine and all the Chairs of the Department met on a daily basis to discuss a plan of action. It was a fast way for a new Chair to learn. Finally, at the last meeting in the house of the President of the University, the decision was made to ask the Dean to resign. Not surprisingly, the task to speak to the Dean was given to the Chair of the Department of Psychiatry. For one year there was an Interim Dean until Dr. A. Aberman was appointed. Thus, Mladen had the unusual circumstance of serving under three quite different Deans of Medicine.

The Department of Physiology at the University of Toronto was founded in 1887 and has an illustrious history. One of the most prominent Chairs was Dr. A.B. Macallum (1891-1917), whose legacy was the recognition of the importance of research in addition to teaching. Dr. J.J. Macleod (1918-1928) was one of the worlds' leading physiologists with a particular reputation in the field of carbohydrate metabolism. He provided the facilities and physiological “know-how” for the discovery of insulin, which is credited to Banting, Best, Macleod and Collip. The Nobel Prize, the first to Canadians, was shared by Banting and Macleod. Dr. Charles H. Best became Chairman in 1929 and continued the 33 year legacy. Departments of Physiology in North America are generally much larger than in Europe because they embody both primary and cross-appointed members from other departments. They all share teaching commitments and participate in the supervision of graduate students. The total number of assistant, associate and full professors in our Department of Physiology at the present time is about 100. Mladen was very keen to strengthen the relationships between the Departments of Physiology and Medicine. This close collaboration between Physiology and Clinical Departments resulted in many ventures covering the whole spectrum of research, from molecular biology to clinical trials. All endocrinologists in the Department of Physiology are cross-appointed to the Clinical Division of Endocrinology of the Medical School. This initiative of bringing basic and clinical departments closer together was further strengthened by his successor, Dr. John Challis, a reproductive physiologist. With the crisis in the Medical School, the Department of Physiology was very uncertain about its future as an independent department, which created great malaise. A most important role was to unify the department with respect to primary and cross-appointed members. Research within the department is carried out exclusively through external granting funds. During Mladen's chairmanship, the inflow of grants for research reached a level comparable to the strongest Departments of Physiology in North America. He also tightened the administrative structure of the department, which was very fortunate because two years after assuming the Chair, he needed an emergency quadruple heart bypass. For a few months, the Deputy Chair of the Department ensured continuity.

In October 1996 he was the Chairman of the Committee to celebrate the 75th anniversary of the discovery of insulin in the Department of Physiology. Delegates from over 50 countries, including Croatian diabetologists, participated in what was a very strong scientific program that commemorated what Dr. Michael Bliss calls one of the most dramatic adventures in the history of medicine. 

An important recognition came in 1997 when he had the honour of being elected as a Corresponding Member of the Croatian Academy of Arts and Sciences on the recommendation of Drs. Skrabalo, Padovan and Kastelan. Since the time that Bishop Strossmayer established the Academy over a century ago, it has played a very important role in the academic life of Croatia. The induction ceremony is magnificent, and an exciting opportunity to again meet many of his former professors and colleagues. Dr. Zeljko Metelko, now Director of the Diabetes Centre in Zagreb, took Suad and Mladen to show them some of the areas which were completely devastated by the war. Later the same year, he had the second honour of being elected into the Royal Society of Canada (Canadian Academy of Arts & Science). The Royal Society of Canada was founded just a few years after the Croatian Academy. The induction was carried out in the Parliament Buildings in Ottawa, the capital of Canada.

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There are eight interdependent, projects with the main goal of understanding aspects of the pathogenesis of diabetes, including exercise, stress and hypoglycemia.

1) Extrapancreatic Glucagon

Since the discovery of insulin it was clear that diabetes is related to insulin deficiency. What was not known was whether glucagon, the second hormone of the endocrine pancreas, also played an important role in physiology and diabetes. There were two reasons for this: 1) Glucagon can increase glucose in plasma but only when given at very high concentrations; 2) Diabetes can be induced in animals either by selective chemical destruction of the insulin-producing B-cells or by total pancreatectomy, which removes the B-cells and the glucagon-producing A-cells. If glucagon were the hormone to counteract insulin, one would have expected that total pancreatectomy would induce milder diabetes than the selective destruction of the B-cells, but that was not the case. Dr. Unger from Dallas, Texas developed an immunoassay of glucagon and at least three laboratories, including his own, claimed that pancreatectomy in dogs results in the total disappearance of glucagon from blood. Mladen's first post-doctoral fellow, Dr. Kawamori, came from Japan. He is presently Chairman of the Department of Medicine at the Tokyo Juntendo Medical School and many of his medical residents trained in Mladen's laboratory. In this way, the contact and collaboration with Dr. Kawamori has continued over many years. When the pancreas was removed from dogs and they were not treated with insulin, glucagon in blood did not disappear (measured by Dr. S. Pek from the University of Michigan), but instead increased to very high levels. These results created a lot of excitement because it was contrary to the dogma. Mladen was so active discussing his views that a friend remarked that it seemed he was speaking in two conference rooms at the same time. It was his first major scientific battle won. This led to the discovery, stunning at the time that a pancreatic hormone can be produced in large amounts outside its original endocrine gland. Over the next ten years using tracer methods to measure glucose fluxes, biochemical, histological, electron microscopy, immunological methods and purifying stomach glucagon to homogeneity, they determined beyond a doubt that the parietal mucosa of the dog stomach can synthesize and secrete true glucagon while the remaining gastrointestinal tract does not produce glucagon but glucagon-like peptides instead. In Toronto he collaborated with Dr. C. Yip and in Geneva with Drs. Jeanrenaud, Miller, Girardier, Prentki and Renold (3,4).  This explained why, following pancreatectomy, diabetes is as severe as with selective destruction of the B-cells:- because the stomach can produce the same amount of glucagon as the pancreas. Interestingly, in one dog that was sacrificed 5 years after pancreatectomy, he showed in collaboration with Dr. Orci in Geneva that there was an incredibly large hyperplasia of the A-cells in its stomach. By electron microscopy the parietal mucosa of the stomach looked like a glucagon-producing endocrine gland. These findings changed some classical views of endocrinology and provided further proof that one hormone is not necessarily produced in only one endocrine gland.

The most exciting symposium that he attended was a 1974 Conference on Glucagon held at the Santa Ynez ranch in California. This property belonged to Mr. Kroc, founder and owner of McDonald's. The scientific program was administered by his brother, Dr. Robert L. Kroc. A few years before the conference there were major breakthroughs in the field of glucagon research and 12 scientists, including Mladen, lectured on these breakthroughs. Guilleman discovered somatostatin and some other hypothalamic-releasing hormones and received the Nobel Prize for this work shortly thereafter. Somatostatin suppresses secretion of glucagon and insulin and therefore it became possible, with the replacement of one pancreatic hormone to precisely determine the distinct functions of insulin and glucagon. Roger Unger provided the evidence that diabetes is not only caused by insulin deficiency but also by glucagon excess. Mladen's discovery of extrapancreatic glucagon in dogs was essential to confirm Unger's suggestion that diabetic hyperglycemia requires no only hypoinsulinemia, but also the presence of glucagon. Marty Rodbell suggested that G-proteins act as transducers in cell signaling by glucagon and other hormones. He received the Nobel Prize for this discovery 20 years later. The highest awards given in North America for diabetes research are the Lilly Award for Young Researchers, and the Banting Medal and Lectureship for Life Achievement. The participants at this particular Kroc Symposium would in the future be recipients of 7 Banting Medals, 5 Lilly Awards, 3 Claude Bernard Medals (the highest European Award for Diabetes Research) and 2 Nobel prizes.

2) Tracer Methods to Measure Glucose Fluxes

Tracer methods are a necessary tool because a change in glucose turnover can occur independently of the changes of glucose concentration. For example, if the pancreas releases insulin and glucagon at the same time, glucagon will increase glucose production by the liver while insulin will increase glucose uptake to the same degree. Using tracer methodology, Mladen showed glucagon's exquisite potency with only physiological amounts given. This explained why previous workers not using tracer methods believed that glucagon could exert effects only in very high amounts and in many organs, which could not explain its physiological role. Mladen showed that in physiological doses glucagon is very selective, acting only on the liver.

It is easy to measure glucose turnover in steady state. However, if one wishes to learn how various control systems work it is necessary to drive the system out of steady state. Drs. Steele, Altszuler and De Bodo in Brookhaven developed a mathematical model to do just this. Their model was based on certain assumptions regarding the distribution of glucose in extracellular fluid. The problem with their model was that it was not experimentally validated. It had been used only in dogs with uncertainty about the precision of the measurements. The first validations, performed in Toronto by Hetenyi and Cowan, provided information about averaged data over an entire experimental period. Dr. Geza Hetenyi came to the Department of Physiology at the C.H. Best Institute during the Hungarian revolution and played a key role as Mladen's mentor in both science and music. Mladen argued that the question was not whether such tracer methods were right or wrong, but that what is important is to determine the error throughout an experiment or clinical trial. Dr. J. Radziuk, a graduate student of Dr. K. Norwich and Mladen (5), compared the results of one tracer whose infusion rate was known, against the results of a different tracer whose infusion rate was unknown. In this way they could check the accuracy of the methodology on a minute-to-minute basis throughout the period of change. They concluded that the methodology, which Hetenyi and Cowan modified from the original proposal of Steele, had an error of only 10%. It also implied, however, that comparisons of two experimental conditions are only valid if the difference is much larger than the error of the method. The validation studies convinced clinical investigators that this methodology could be used with confidence. Application of non-steady state glucose turnover enabled him and his colleagues to study the selective effects of metabolic hormones (glucagon, insulin, catecholamines, IGF-1, glucocorticoids) and their interactions. This is a cornerstone for understanding the physiology of metabolic hormone actions as related to pathogenesis of diabetes, stress and exercise. With a close friend and colleague, George Steiner, they conducted the first clinical studies, using the validated tracer infusion method. This is now a standard method for measuring glucose turnover in man. They used the non-steady state approach for the first time to demonstrate that insulin resistance is present not only in obesity but also in lean, hypertriglyceridemics (6). It was known that obesity leads to insulin resistance but what was amazing was that the same degree of insulin resistance could be demonstrated in lean subjects with lipid disorders. With a double tracer technique they also quantified the role of the Cori cycle (recycling of glucose from liver to periphery and back) in metabolic adaptations. An important metabolic adaptation is that during fasting glucose production decreases, which minimizes protein degradation in muscle, the main source of gluconeogenesis. However, the most important mechanism for reducing gluconeogenesis is to recycle glucose through the Cori cycle, thus minimizing the need for carbon from amino acids to produce glucose. They determined for the first time that during fasting, the absolute rate of glucose recycling is unchanged, but since glucose production decreased, the proportion of glucose production, which was represented by recycling increased.  The collaboration with George prompted his interest in clinical research and stimulated him to strengthen the ties between physiology and medicine. Many basic scientists were apprehensive about breaking the barriers between themselves and clinical researchers. This has greatly changed since each large teaching hospital now has its own research Institute and since cross-appointments between various departments are flourishing.

The Federation of American Societies of Experimental Biology (FASEB) holds a Symposium every year to consider problems and advances of tracer methodology. he became Chairman and organizer of the Tracer Methodology Study Group in 1972 and continued until 1975. This was a very exciting task, especially when he became the first person asked to edit and publish the Proceedings from this Symposium in Federation Proceedings, a very prestigious and widely read journal.

The main method used to assess insulin's effects in vivo is the euglycemic, hyperinsulinemic clamp developed by Dr. Andres at National Institutes of Health. This is a critical method in diabetes because it can assess the magnitude of insulin resistance. With the clamp combined with tracers, one can assess hepatic glucose production separately from overall glucose utilization. The problem observed in every laboratory was that glucose production measurements were frequently negative, an artefact that invalidated the measurements. With a post-doctoral fellow, Dr. Diane Finegood, and in collaboration with Dr. Richard Bergman of the University of Southern California, they established a new methodology whereby the tracer infusion was not constant. They were able to predict variations in tracer infusion such that specific activity of glucose could be maintained constant and thereby the measurement of glucose production became very precise (7). Bergman and he developed a close friendship with an active exchange of ideas well beyond their scientific interests. This tracer method is now generally accepted as state-of-the-art methodology. However, when a glucose clamp is not used, one cannot predict precisely the changes in specific activity that will occur. Using different models, he nevertheless showed that it is possible to minimize the changes in specific activity and demonstrated that accurate data could be obtained if the change in specific activity is under 25%.  This new method was used in collaboration with Errol Marliss, from McGill University, for the first time during strenuous exercise, when rapid increments of glucose turnover occur within minutes and therefore the new tracer method is particularly essential (24).

Advances in tracer methodology opened the door for very precise investigation of the hormonal interactions and teleology. With Alan Cherrington, then a graduate student, he demonstrated how precisely glucagon and insulin need to interact to increase glucose turnover but maintain glucose homeostasis (8). With Friedrich Kemmer, a postdoctoral fellow from Germany, and colleagues O. and A. Sirek they solved an old problem. The question was why hypophysectomy can under certain conditions normalize plasma glucose in diabetes. They demonstrated that this is due to a decrease of glucose production, which is itself in part due to normalization of glucagon secretion. Contrary to earlier views, hypophysectomy deteriorated peripheral glucose uptake (9). With postdoctoral fellows, Kamil El-Tayeb and Pat Brubaker, and surgeon, Dr. Lavina Lickley they demonstrated that beta-endorphins, which are known to have opiate-like effects during stress, also have important effects on glucose metabolism. They potentiate epinephrine's hyperglycemic effect both by increasing glucose production and decreasing peripheral glucose clearance.

3) Exercise and Diabetes

Mladen's mentor in Toronto, Gerry Wrenshall, was a Type 1 diabetic. It was general knowledge that exercise improves metabolic control in diabetes and therefore he would go for a fast walk after each meal. They began exercise experiments in depancreatized dogs that were either infused with or totally deprived of insulin. The surprise was that in uncontrolled diabetic dogs during exercise, blood sugar did not decrease but instead it sharply increased due to an excessive increase in hepatic glucose production. The main beneficial effect of exercise in normal man and animals is an increase of glucose metabolic clearance. Glucose clearance reflects the efficiency of tissues to extract glucose independently of glucose concentration. This parameter is very important for the study of regulation of glucose transport because glucose concentration by itself promotes glucose utilization. They were the first to promote this concept in their first published exercise paper (10). In contrast to normal dogs, in diabetic animals glucose clearance did not increase. It was even more disturbing that an intraportal insulin infusion that decreased plasma glucose from 350 to 140 mg% still resulted in an increase of plasma glucose without the increase of glucose clearance during exercise. Clearly an acute basal intraportal insulin infusion did not improve insulin resistance. These experiments in dogs consisted of a 100m/min run on a flat treadmill, reflecting light exercise. In later experiments they increased the incline by 12% to reflect more intense exercise. It was interesting that under those conditions a basal insulin infusion could indeed normalize glucose turnover, illustrating the importance of the level of difficulty of exercise.

When Berson and Yallow developed the immunoassay for insulin in the sixties, it became evident that during exercise in non-diabetic subjects, insulin in plasma decreases up to 50%. Mladen hypothesized that since blood flow in muscle during exercise can increase by 20-fold or more despite a decrease in plasma insulin, the perfusion of muscle with insulin is maintained. Other laboratories indicated that muscle contraction increases glucose uptake independently of insulin. Mladen concluded that insulin during exercise in vivo is necessary to counterbalance factors that would decrease glucose uptake such as increased fatty acids and catecholamines (11). They then examined the mechanism of exercise-induced hypoglycemia in depancreatized dogs maintained on long-acting insulin. With Kawamori, he was very surprised to find that during exercise, plasma insulin increased dramatically. It was interesting that nobody had made this observation before, although the insulin assay had been available for quite a few years. A friend remarked at the time that what he observed was highly unlikely since it would surely have been noticed before. Nevertheless, he could now for the first time explain the mechanism of the development of hypoglycemia during exercise in insulin-treated patients (12). With increased insulin levels during exercise, glucose production did not increase to match the increased glucose uptake by the muscle. Even when insulin does not increase, the fact that exogenous insulin does not decrease may also inhibit the liver, but to a lesser extent. During his sabbatical leave in Geneva working with Michael Berger, Philippe Halban, (now President of the European Association for the Study of Diabetes) and Albert Renold he injected tritiated insulin, which was synthesized for the first time by Halban. This gave them the opportunity to study the pharmacokinetics of insulin absorption in rats running on a treadmill. Mobilization of insulin from its subcutaneous depot increased dramatically and most of the radioactive insulin was found in skeletal muscle. This also confirmed their hypothesis that during exercise perfusion of muscle with insulin can increase, presumably due to increased blood flow in the muscle (13). In collaboration with Drs. Zinman and Marliss in Toronto, they were then able to demonstrate the same observations in Type 1 diabetics. The diabetic subjects in which insulin infusion established near-normal plasma glucose had normal turnover rates in exercise. With injection of insulin, however, plasma insulin increased in the same fashion as in dogs and rats and again the increment of glucose production was prevented (14). He thus developed a hypothesis that explained why exercise in diabetics can result in unchanged glucose levels, in hyper- or hypoglycemia and this hypothesis was widely accepted. With insulin deficiency or resistance, there is overproduction and underutilization of glucose, and hyperglycemia ensues. On the other hand, with excessive insulin due to enhanced mobilization from its subcutaneous depot, glucose production is inhibited and its utilization is enhanced.

In Oxford, U.K., he worked in the laboratory of Eric Newsholme. Phosphorous nuclear magnetic resonance spectroscopy offered an opportunity to study intracellular pH and phosphocreatine continuously and non-invasively. This was done in collaboration with John Challis and George Rada and was the first NMR spectroscopy of muscle performed in diabetic rats (15). During muscular contractions in diabetic rats that were not insulin-treated, the bioenergetics studied were deficient.  Insulin-treated rats were normal. The big surprise was that if insulin treatment was discontinued for three days all the parameters studied remained normal. This clearly indicated that the continued presence of normal insulin values is not needed for glucose metabolism during exercise. The deficiency of diabetic rats with respect to muscular contraction was thus a consequence of chronic effects of the diabetic state. However, an effect of acute insulin withdrawal was observed in the post-contractile state. The rate of resynthesis of glycogen was greatly diminished. It is now well known that this defect is observed not only in diabetes, but also in non-diabetic offspring of diabetic parents.

Guilleman's discovery of somatostatin permitted him to study with Dr. B. Issekutz from Halifax, for the first time, the role of glucagon in regulation of glucose production during exercise in normal dogs (16). Dr. Issekutz left his native Hungary during the revolution, and was a pioneer is studying the effects of exercise on glucose and FFA turnover. A suppression of glucagon greatly decreased the increment of glucose production, resulting in hypoglycemia during exercise. This greatly changed the type of fuel utilized by the muscle. Hypoglycemia resulted in an increased release of catecholamines, which suppressed muscle glucose clearance but increased lipolysis. They demonstrated, and it is now widely accepted, that the main regulator of glucose production during moderate exercise is the ratio of glucagon to insulin. By preventing the drop in plasma glucose he was able to determine, with Ph.D. student D. Wasserman and in collaboration with Dr. L. Lickley, that glucagon controls most of the glucose production increment (17). Dr. Lickley is a surgeon who divided her main interest between breast cancer and experimental diabetes. She is a close friend and Head of Surgery in Women's College Hospital in Toronto. This collaboration continued for 20 years. The conclusion was that an important role of glucagon during exercise is to spare muscle glycogen by stimulating glucose production by the liver. This is of particular importance for repetitive or endurance exercise. Glucagon is even more important in exercising, diabetic dogs where suppression of glucagon completely prevents increments in glucose production (18). They also demonstrated that in diabetes defective glucose clearance during exercise can be fully normalized by the beta-blockade of catecholamines but only if some insulin is present. This clearly demonstrated that the main role of insulin during exercise is not its direct effect on the muscle but rather to counteract the negative effects of catecholamines on glucose utilization. The field of metabolic control and exercise and diabetes was reviewed with the late Michael Berger, former President of EASD (19).

He had a very productive and enjoyable collaboration with Dr. Amira Klip. It was known at the time that glucose is transported into various tissues by specialized proteins-glucose transporters. A stunning discovery by Cushman and Kono was that in the fat cell, by far the largest number of transporters is found in cell plasma and that insulin translocates the transporters to the plasma membrane where they exert their function. It was much more difficult to determine glucose transporters in the muscle and Amira was one of the first to develop the methodology required for the muscle. They demonstrated, together with a graduate student D. Dimitrakoudis, that in mild diabetic rats, glucose transporter number is decreased both in plasma membrane and inside the cell and that this was due not to insulin deficiency, but to hyperglycemia. They explored this problem using phlorizin. Since the time of Minkowski, more than 100 years ago, it had been known that phlorizin prevents reabsorption of glucose in the kidney. Therefore, it is possible to normalize glucose in diabetic animals by phlorizin treatment. Plasma glucose is normalized because excessive amounts of glucose are secreted in the urine. When they treated diabetic rats with phlorizin for a few days, glucose concentration normalized and they could normalize not only the number of glucose transporters but also the genetic expression of the gene for glucose transporters in the muscle (20).

This work with Amira continued with a post-doctoral fellow, Dr. Marette. They showed for the first time that most of the glucose transporters are translocated not to the plasma membrane, but to the transverse tubules of the skeletal muscle. This is physiologically very important because transverse tubules represent a larger surface area than the plasma membrane, are exposed to the extracellular milieu and play an important role in transporting ions and nutrients into the muscle fibre. A Ph.D. student in their laboratories, Theos Tsakiridis, demonstrated that the actin network, an important part of the cytoskeleton, is essential for the insulin stimulation of glucose transport and transporters (21). However, they further concluded that this network might be part of the signaling process rather than only a simple vehicle for transport of the vesicles. This was particularly evident when the stimulation of glucose transport was caused by mitochondrial uncoupling of the oxidative chain. This was achieved by dinitrolphenol, which mimics the effect of hypoxia and perhaps exercise. This signaling process was completely different from that with insulin. The key signals required for insulin stimulation, phosphatidylinositol 3-kinase and the actin network were not required when the oxidation chain was uncoupled (22). This observation, with observations from other laboratories explains why the effects of insulin and exercise are additive and why muscular contraction per se can stimulate glucose transport without insulin.

An ongoing collaboration with Errol Marliss from McGill University examines the effect of strenuous exercise in normal and Type 1 diabetic subjects. In contrast to his previous work in man and animals during moderate exercise, the changes in glucagon and insulin during strenuous exercise are not important in hepatic regulation of glucose production. This was demonstrated by using somatostatin infusions to clamp insulin, glucagon and growth hormone so that the secretion of those hormones could not be affected by exercise. Because in strenuous exercise, concentration of plasma catecholamines is excessive (16x), they postulated that in strenuous exercise control of glucose production shifts from the glucagon/insulin ratio to the effect of catecholamines (23). This would also imply that during strenuous exercise, mobilization of glycogen in muscle could play a bigger role than mobilization of glucose from the liver, since catecholamines are potent stimulators for both muscular and hepatic glycogenolysis. Interestingly, in contrast to moderate exercise, feeding did not shut down endogenous glucose production, an important mechanism to maintain glucose supply at the highest possible rate (23).

Insulin deficiency results in increased FFA levels, which according to Randle's hypothesis could inhibit peripheral glucose uptake. Mladen investigated this effect during moderate exercise in dogs with a post-doctoral fellow, Dr. Q. Shi and Dr. K. Yamatani from Japan. The main effect of inhibition of FFA oxidation was to decrease glucose production by the liver rather than a direct effect on glucose uptake in the muscle as proposed by Randle. Normalization of glucose production during exercise improved plasma glucose concentration in diabetic dogs, which in turn increased metabolic glucose clearance (MCR) in the muscle. These observations led to the hypothesis about the relationship between glucose concentration and glucose uptake in the muscle, protecting the muscle against excessive hyperglycemia. This will be described in more detail later.

His new early concepts regarding metabolic regulations in physiology and diabetes during exercise attracted wide attention. He was invited to organize the first Symposium on “Exercise and Diabetes” sponsored by the Kroc Foundation in 1978, and held in the same place where he had attended the Glucagon Symposium four years earlier (see books edited). This initiated a number of meetings on this topic, held every three years, in both Europe and the United States. It is generally considered that this conference greatly stimulated research in the field of diabetes and exercise, which is of paramount importance with respect to the disease. More recently, epidemiologists concluded that exercise not only can improve but may also prevent type 2 diabetes. Thus, exercise is considered a cornerstone in the treatment and prevention of type 2 diabetes. With Michael Berger, he wrote a review (24) that has been updated with different collaborators many times in a variety of books, of which the most important are 3, 4, 5, 6th Edition of Ellenberg and Rifkin's Diabetes Mellitus (25).

The last six years we explored the mechanism of preventing hyperglycemia in an animal model of obese diabetic rats (ZDF). These animals have a deficient leptin receptor, and therefore, they eat excessively. With development of obesity, they also develop Type 2 diabetes. In a paper resulting from my D.Sc. in Zagreb, I indicated that new islet cells can originate either from hyperplasia of the islet cells, or from the cells of pancreatic ducts (1). Methodology of that time was very simple: now we have the availability of molecular methods to study the growth of insulin producing beta cells. What is amazing is that with only 1 hour of swimming per day, the rats, although obese, did not develop diabetes. The reason for this is that obese animals and humans are insulin resistant, but they only develop diabetes if the pancreas is unable to release huge amounts of insulin. Exercise stimulated the growth of the beta cells and we could demonstrate marked increase of new beta cells. Increased beta cell mass was also accompanied by an increased function. In diabetes a number of proteins are not processed properly and they accumulate in the beta cells. The prevention of hyperglycemia also prevented accumulation of such proteins and it prevented oxidative stress. We concluded that exercise first, improves uptake of glucose in the muscle (increased insulin sensitivity). High blood sugar is toxic for the beta cells and therefore, their mass and function deteriorates. However, prevention of hyperglycemia also prevents toxic effects on the beta cells. Improvement of the function of beta cells helps to prevent diabetes. Swimming as a modality of exercise is accompanied by stress. We then investigated the effect of volitional exercise where the rats have an opportunity to volunteer exercising in their cages. We observed the same effect. A very hot area of research right now is the fact that low grade infection occurs in obesity. That is an important factor that decreases action of insulin (insulin resistance). We investigated a number of markers of inflammation and could show that despite obesity, exercise attenuates the inflammation. Thus, such work in animals indicates the surprising fact that just one hour of exercise per day can prevent diabetes and strengthen the notion that exercise, and of course food control, are the key factors that can prevent onset of  Type 2 diabetes. When the rats stopped exercising, diabetes developed. This strengthened the notion that in order to prevent diabetes, a continuous, uninterrupted exercise program is needed (41).

It is well known that continuous stress deteriorates diabetes and probably can also accelerate the onset of diabetes. Very surprisingly, that is not the case in all types of stress. When we exposed the obese rats to neurogenic stress (rats are put into plastic tubing which restrains their movements), the onset of diabetes was also prevented. Physiological and molecular analysis indicated that this type of stress can decrease body weight and decrease the activity of the Hypothalamic-Pituitary-Adrenal Axis, which both have a beneficial effect. This is in the same line with work of the father of stress, Hans Selye. We indicated that certain types of stress improve, rather than deteriorate the health. Importantly, our work contrasts with common views that all stressors are deleterious for diabetes and illustrates that intermittent exposure to mild stressors and the ensuing adaptations may instead be important for normal physiological functioning by preparing the body to deal with threats to homeostasis (42).

4) The Relative Importance of Portal and Peripheral Insulin in Regulating Glucose Production:

One such example is the control of glucose production. Together with Dr. Adria Giacca, a post-doctoral fellow who came from Italy and who is now an Associate Professor in the Department of Physiology, University of Toronto, they demonstrated that in diabetic dogs a peripheral infusion of insulin is more effective in suppressing glucose production by the liver than a portal insulin infusion (26). This was very surprising since the general belief was that increased glucose production in diabetes is at least in part due to the fact that diabetics are treated with peripheral insulin injections. However, some 30 years ago Rachmiel Levine had already indicated this possibility, since insulin has very little effect on isolated liver cells. We thus confirmed an earlier key paper of Richard Bergman that arrived at the same conclusion working in normal dogs. The question arose as to how a peripheral metabolic effect of insulin can send signals to the liver. They investigated this in diabetic dogs and in normal and diabetic human subjects. Insulin cannot be delivered intraportally in humans, so in collaboration with Dr. Gary Lewis they infused tolbutamide to stimulate endogenous insulin secretion. Two weeks later they infused insulin peripherally and were able to mimic insulin secretion rates produced by tolbutamide. They concluded that in normal man, both peripheral signals and direct hepatic insulin secretion are of importance. We speculated that the direct hepatic effect of insulin is initially to inhibit glycogenolysis while the indirect effect of insulin eventually and predominantly suppresses gluconeogenesis. The main peripheral signal is insulin suppression of glucagon and free fatty acids (FFAs) (27). The residual direct effect of insulin is demonstrated when both glucagon and FFA are replaced so that a peripheral signal is abolished. They also concluded that in Type 2 diabetes, the sustained suppression of glucose production is due exclusively to peripheral signals (28).

5) Stress and Diabetes:

The effects of acute and chronic stress are wide-ranging and it is well known that they can markedly offset metabolic control in diabetes. Together with graduate students, P. Miles and M. Lekas, and post-doctoral fellows, Z.Q. Shi and K. Yamatani, Mladen induced acute stress in dogs by inserting a chronic cannula into the third ventricle (29,30). Carbachol injections mimic the muscarinic action of acetylcholine, which is a major neurotransmitter of the brain. Such an injection induces a release of all counterregulatory hormones (vasopressin, cortisol, catecholamines and glucagon). It is known that some types of stress can selectively suppress insulin secretion but in this model, insulin is not affected. In normal dogs, this stress induces a large increase in glucose turnover with only a 5% change in glucose concentration. Glucose homeostasis is maintained because stress induces an increase in glucose utilization that is independent of insulin. This was the first demonstration of a neuroendocrine pathway that can increase peripheral glucose utilization independently of insulin. In contrast, stress induced a major increase in glucose concentration because glucose uptake did not increase, as shown by graduate student Shirya Rashid. Resistance to stress in diabetes reflects a chronic defect that cannot be improved by acute hyperinsulinemic euglycemic clamps. Similarly to exercise, beta-blockade can in part restore the response of glucose uptake to stress (31). Thus they discovered the mechanism whereby stress in diabetes can offset glucose homeostasis.

6) Protection Against Excessive Hyperglycemia of Muscle and Liver, but not Pancreas

The next important invitation was to deliver the 1995 Solomon Berson Distinguished Lectureship of the American Physiological Society - Endocrinology and Metabolism Section at the Federation of American Societies of Experimental Biology in Atlanta entitled “The Yin-Yang of Carbohydrate Metabolism”. He is the only Canadian to have given that lecture.

The ancient Chinese philosophy of the Yin and the Yang can be used as a metaphor for the balance between active and passive interrelationships. In this philosophy, yin is dark and passive, while yang is light and active. In harmony the two are symbolized as the light and dark halves of a circle, and literally mean the dark and sunny sides of a hill. What is particularly useful with respect to glucose homeostasis is the yin-yang implication of an entire series of opposites, whose interplay (as one increases, the other decreases) defines the actual dynamic process. The thesis of his Berson Lecture was the proposition that in some organs, decreased glucose efficiency is not a defect, but rather a protective mechanism against diabetic complications. Glucose utilization is a result of opposing forces related to the effect of glucose itself, and to the interaction between the effects of glucose and insulin. These interactions are dynamic and reflect a continuum of synergistic and contrasting processes. Most of the complications of diabetes are due to chronic elevation of plasma glucose. Through mass effect, an excessive amount of glucose enters a variety of tissues resulting either in glycosylation of many proteins or in augmentation of otherwise insignificant metabolic pathways. This does not occur in either the muscle or the liver.

In diabetes, glucose uptake in the muscle is not decreased. The defect can be observed by measuring metabolic glucose clearance (MCR), which represents the ratio of glucose utilization to plasma glucose concentration and reflects the efficiency of glucose extraction by the tissues. Glucose clearance is significantly decreased in diabetes, which is one reason for development of hyperglycemia. This was attributed to a toxic effect of hyperglycemia on glucose uptake in peripheral tissues. He suggested that this is mainly an adaptive effect. Together with Dr. Geza Hetenyi, a former Chairman of the Department of Physiology at the University of Ottawa, they infused phlorizin to diabetic dogs either for a few days or acutely. The only effect of phlorizin is the prevention of glucose reabsorption by the kidney, causing glycosuria. With chronic or acute glucose normalization the defective glucose clearance substantially increased, providing the evidence that most, if not all of the diabetic defect was adaptive and could be fully normalized in dogs after many months. In his recent experiments (32) performed with an MD/PhD student, S. Fisher, he demonstrated that during exercise the severe defect of MCR in diabetic dogs was fully restored by an acute normalization of glucose by phlorizin and this was independent of FFA turnover and insulin levels. This demonstrates that regulation of glucose uptake during exercise is mainly dependent on muscular contraction and not insulin or FFAs. However, the energy balance in the muscle was maintained because when the FFA turnover was high, glucose oxidation decreased. In contrast to MCR, glucose uptake was near normal during rest and exercise in both normoglycemic and hyperglycemic dogs. However, because of decreased glucose transporters as described earlier, glucose clearance also decreases so that the net result is that the changes of glucose uptake are minimized. With Marliss, he demonstrated the same phenomenon in Type-1 diabetic patients whose plasma glucose was maintained overnight with insulin infusion at moderately hyperglycemic levels. During rest and strenuous exercise glucose utilization was normal. However, metabolic clearance rate (MCR) was decreased during rest and exercise (33). Again, this illustrates a perfect balance between glucose concentration and glucose MCR. However, because of low MCR blood sugar did not decrease following exercise, as it did in non-diabetics. This implies that diabetic subjects who require less insulin during and after moderate exercise, may require additional insulin injections following strenuous exercise (23). With Dr. Shi and graduate student, J. Mathoo, He demonstrated that the same mechanisms also work in the isolated hindquarter of the rat. In the total absence of insulin by appropriate infusions of glucose they kept plasma glucose concentrations normal, hypo- or hyperglycemic. With hyperglycemia, the number of glucose transporters in plasma membrane decreased while with hypoglycemia it increased. This was reflected with increased or decreased rates of MCR. Thus, during rest and exercise the muscle is protected against hypo- or hyperglycemia. Other laboratories have investigated the reason for muscle resistance against insulin, which also diminishes glucose uptake. However, both mechanisms contribute to diabetic hyperglycemia, which causes diabetic complications in other organs.

7) Glucose Cycling:

Glucose uptake in the liver is modified by three non-equilibrium reactions:- the glucose cycle, the fructose-6-phosphate cycle and the phosphoenol pyruvate cycle. Suad and Mladen were particularly interested in the glucose cycle in which entry of glucose is accelerated by the enzyme glucokinase, which yields glucose-6 phosphate. Some of the glucose-6 phosphate is then cycled back into glucose through the enzyme glucose-6 phosphatase. Thus through this mechanism a small amount of glucose taken up by the liver is recycled into the blood stream. They found that the activity of glucose cycling was increased in depancreatized and alloxan-induced diabetic dogs, in lean and obese Type-2 diabetic subjects as well as in acromegaly and hyperthyroidism (34,35). The percent increase in post-absorptive glucose cycling is more marked than the increase in glucose production. They suggested, therefore, that measurement of glucose cycling in addition to glucose production could be a valuable tool to assess the early metabolic derangements of glucose intolerance. The mechanism of increased glucose cycling in depancreatized dogs was then investigated (36). With Drs. Shi, Giacca and van der Werve, Chairman of the Department of Nutrition at the University of Montreal they measured liver enzymes by biopsy and glucose cycling by the double tracer method during anaesthesia. They concluded that increased hepatic glucose cycling from diabetes is mainly due to the increase of substrates for glucokinase and glucose-6 phosphatase rather than from changes in the total amount of enzymes. This has some similarity to regulations in the muscle because again glucose concentration by itself can regulate part of its rate of entry into the liver. It is not known how effective this mechanism is in reducing excessive metabolism of glucose into the liver.

8) Hypoglycemia:

A major acute complication of diabetes is a defective response of glucagon, catecholamines and glucocorticoids to insulin-induced hypoglycemia. The threat of hypoglycemia has increased since the treatment for diabetes has aimed for tight blood glucose control to decrease the risk of diabetic complications. Therefore, it is very important to develop a treatment strategy that would decrease the risk of hypoglycemia. The defect of glucagons and epinephrine response to hypoglycemia is puzzling because both counterregulatory responses are normal or even excessive during some stresses, such as moderate and strenuous exercise (23). Mladen tried to answer this question in dogs and rats by inducing diabetes by alloxan and streptozotocin, respectively. With this treatment, not only are most of the beta-cells destroyed but also the number of islets is markedly reduced. With Drs. Sudha Rastogi and Suad Efendic he showed that although in each islet the number of glucagon cells is greatly increased the total amount of glucagon in pancreas remains unchanged because of the reduction in the number of islet cells. It is well known that the release of glucagon by the pancreas is inhibited by both insulin and somatostatin. Since most beta-cells have been destroyed, somatostatin is the main paracrine inhibitor of the A-cell in diabetes. That is why it is of particular interest that in diabetic islets the ratio of somatostatin to glucagon is markedly increased. An acute insulin injection increased this ratio further. Theirs was the first demonstration that part of the defective mechanism in hypoglycemia may reflect alterations of this ratio in diabetes. Since somatostatin inhibits glucagon release, this could explain why glucagon-producing alpha cells are less sensitive to hypoglycemia, while they remain normally responsive to other stresses (37). The other factor that affects alpha cells is chronic hyperglycemia. With Dr. Shi (38) he then demonstrated that the defective glucagon responses are in part due to chronic hyperglycemia and hyperinsulinemia. Normalization of hypoglycemia without, but not with insulin, restored in part, glucagon's responsiveness in diabetic rats. This occurs because hyperinsulinemia offsets the beneficial effect of normalization of glucose.

Presently, he is investigating with Dr. Steve Matthews, a molecular neuroendocrinologist in the department, and graduate student Owen Chan, the gene expression of stress hormones and their receptors in the brain to find out how diabetes affects the function of the hypothalamic-pituitary-adrenal (HPA) axis and its relationship to sympathoadrenal responses in hypoglycemia. They demonstrated that diabetes increases the activity of the HPA axis, which is evidenced by increased expression of stress hormones and their receptors in the brain and by an increase of peripheral glucocorticoids. The impaired stress responses involved also decreased pituitary and adrenal sensitivity, and the basal hyperactivation of diabetic HPA axis is due to decreased glucocorticoid negative feedback sensitivity. With insulin treatment, glucocorticoid concentration normalizes but central components of the HPA axis remain increased. Since the central HPA axis is also associated with sympathetic activity, this could explain why insulin-treated diabetics retain a defect of the sympathoadrenal response to hypoglycemia. Response of the HPA axis to hypoglycemia is greatly reduced in diabetic rats. Normally during hyperglycemia expression of corticotrophin-releasing hormones increases and the expression of mineralocorticoid hormones decreases. That does not occur in diabetic rats. They also demonstrated that normalization of plasma glucose with or without insulin treatment can normalize the responses of the HPA axis to hypoglycemia. Thus, hyperglycemia and not hypoinsulinemia plays a key role in the fine turning of the HPA axis (39). It is well known that repetitive (antecedent) episodes of hypoglycemia increase the threat of further hypoglycemia episodes. They investigated with graduate student, Karen Inouye, the reason why counterregulatory resonses of epinephrine are deficient (40). They demonstrated that there is a defect of enzyme expression in the adrenal medulla that controls epinephrine and norepinephrine synthesis, which is further jeopardized with antecedent hypoglycemia. This could explain the main defect, which is diminished epinephrine response. This indicates the importance of the regulation of synthesis of those enzymes and opens new possibilities for pharmacological intervention.

When we treated the rats with insulin we could normalize glucagon and epinephrine defects, but the defect of the HPA axis persisted. Our insulin treatment normalized fasting blood sugar, but a moderate defect of fed blood sugar persisted. We therefore concluded that full restoration of counterregulation would only be possible if the control of blood sugar is fully normalized, which at the present time cannot be achieved.

We were then interested whether recurrent restraint stress also increases the threat of hypoglycemia similarly to the effect of episodes of antecedent hypoglycemia. Indeed in diabetic rats, these two effects (antecedent hypoglycemia and antecedent stress) were comparable with respect to the HPA axis. The defect correlated with decreased basal gene expression of PVN AVP and the anterior pituitary POMC mRNA. In these rats, there was practically no glucagon response to hypoglycemia and therefore, recurrent restraint stress could not further jeopardize glucagon responses. However, in contrast to antecedent hypoglycemia, recurrent restraint stress did not impair catecholamines counterregulation.

In this biographical sketch, a long journey has been taken to describe Mladen's research endeavours, which are all related to the physiology and pathophysiology of carbohydrate metabolism with a special emphasis on diabetes. To bring it all together, it would be useful to quote the citation that was read during his induction into the Royal Society of Canada: “He pioneered tracer methods for nonsteady-state glucose turnover, providing a cornerstone for quantifying hormonal interactions in glucoregulation and pathogenesis of diabetes. He established the significance of glucagon-insulin interaction in health and diabetes. His hypothesis concerning factors that determine beneficial or deleterious glucoregulatory effects of exercise in diabetes is universally accepted. He demonstrated by tracer, cellular and molecular methods how muscle, liver and pancreatic a-cells adapt to hyperglycemia: a critical concept in diabetes. By purifying and determining biological activity of stomach glucagon, he provided the first evidence of glucagon's extrapancreatic site, changing prevailing concepts that one hormone is synthesized in one gland.”

Mladen has received several awards and honours for his work:

  • Albert Renold Award of the American Diabetes Association for distinguished career in the training of diabetes research scientists and facilitation of research (the only Canadian awarded) (2005),
  • Keynote speaker on Endocrinology and Diabetes;
  • The society of Chinese Bioscientists of North America (2006),
  • Canadian Diabetes Association Inaugural Life - Time Achievement Award for leadership in diabetes research and contribution to the Canadian diabetes community (2007),
  • Fellow, Royal Society of Canada (FRSC);
  • Corresponding Member, Croatian Academy of Arts and Sciences;
  • Poll Visiting Scholar, University of Washington, Seattle, Washington;
  • Novo Nordisk Lecture, Karolinska Institute, Stockholm;
  • Solomon A. Berson Distinguished Lectureship of American Physiological Society - Endocrinology and Metabolism Section, FASEB, Atlanta;
  • Foreign Adjunct Professor, Karolinska Institute, Stockholm; Mizuno Inaugural Lectureship and Award, Fourth International Symposium on Exercise and Diabetes - Osaka University, Japan;
  • Honorary Degree of Doctor of Medicine - Karolinska Institute Medical Faculty (one of the two Canadians in the whole history of Karolinska institute);
  • Banting Medal and Lectureship For Distinguished Scientific Achievement (American Diabetes Association – the only Canadian working in Canada);
  • R. Kroc Lectureship, University of Southern California School of Medicine, Los Angeles;
  • Peter J. Laurie Memorial Lecture of the Juvenile Diabetes Foundation Canada, Toronto; Canada Council Killam Scholar;
  • Elected Fellow of the Royal College of Physicians and Surgeons of Canada, Medical Scientist Category;
  • MRC Visiting Scientist Award during sabbatical leave at University of Oxford, England;
  • Visiting Research Fellowship at Merton College, University of Oxford, England;
  • Inaugural Banting and Best Memorial Lecture and Canadian Diabetes Association Award: 12th Congress of the International Diabetes Federation, Madrid, Spain;
  • Pfizer Lecturer and Travelling Fellow of the Clinical Research Institute, University of Montreal;
  • Upjohn Lecturer of the Faculty of Health Sciences, University of Ottawa;
  • Vuk Vrhovac Memorial Lecture, University of Zagreb, Croatia (to commemorate the 50th Anniversary of the Foundation of the Institute for Diabetes);
  • Faculty Scholar of the Josiah Macy Foundation during sabbatical leave at the University of Geneva;
  • Elected Professor, Department of Medicine, University of Zagreb;
  • Honorary Executive Member of the Croatian World Congress Physicians;
  • Diploma for contributions to Medical Science and Health in Croatia, on the occasion of the 125th anniversary of the Medical Council of Croatia;
  • Honorary member of the Turkish Diabetes Association.
He was Chair or Co-chair of 15 Organizing Committees of Scientific Meetings or Symposia, and he has been invited to lecture at 140 Universities and Symposia internationally.

Please, go to the next page below.




In closing, Mladen's greatest pride is in his students and post-doctoral fellows who are so well recognized internationally. To mention a few:

  • Ryuzo Kawamori, Chair of Department of Medicine, Juntendo University, Tokyo, Japan and President of the Japanese Diabetes Association;
  • Patricia Brubaker, Professor of Physiology and Medicine, Canada Research Chair in Physiology and Associate Chair of the Department of Physiology;
  • Adria Giacca, Full Professor, Department of Physiology, University of Toronto;
  • Alan Cherrington, Chair of the Department of Molecular Physiology and Biophysics, Vanderbilt University, Former President, American Diabetes Association;
  • David Wasserman, Professor, Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville;
  • Andre Marette, Professor of Anatomy and Physiology, FRSQ National Scientist, Chair CIHR Research Team on Cardiovascular Complications of Diabetes Associate Professor, Laval University, Quebec;
  • Jerry Radziuk, Professor of Physiology and Medicine, University of Ottawa;
  • Diane Finegood, Scientific Director, CIHR Institute of Nutrition, Metabolism and Diabetes, Professor of Physiology and Medicine, Simon Fraser University, British Columbia;
  • Qing Shi, Medical Director, Amphastar Pharmaceuticals, Rancho Cucamonga, Adjunct Profesor, Department of Physiology, University of Toronto;
  • Kunhiro Doi, President Japan Clinical Diabetes Society;
  • Philippe Holbone, Professor University of Geneva, Former President, European Association for the Study of Diabetes;
  • Ola Bjorkman, Managing Director Stockholm – Upsalla Science Park;
  • David Lau, Professor of Medicine and Director of the Julia McFarlane Diabetes Research Centre, University of Calgary, Alberta;
  • Friedrich Kemmer, Professor and Chair, Department of Nephrology and Endocrinology, State Hospital, Brandenburg, Germany.
This does not even mention a number of younger scientists who have yet to make a name for themselves. A special privilege has been the friendship of a large number of collaborators in the borderless, international milieu that is science.

Selected Bibliography (from a total of over 290 published papers and chapters)

  1. Vranic M. The effects of cortisol on guinea pigs with normal and atrophic exocrine pancreas. Diabetes 14:194-200, 1965.
  2. Vranic M. Professor Charles H. Best. In: Excellent Teachers: Intellectual Roots of the Royal Society of Canada (ed. A.C. Michalos), Althouse Press, 2003 In Press.
  3. Muller WA, Girardier L, Seydoux J, Berger M, Renold AE and Vranic M. Extrapancreatic glucagon and glucagon-like immunoreactivity in depancreatized dogs: a quantitative assessment of secretion rates and anatomical delineation of sources. J Clin Invest 62:124-132, 1978.
  4. Doi K, Prentki M, Yip C, Muller W, Jeanrenaud B and Vranic M. Identical biological effects of pancreatic glucagon and a purified moiety of canine gastric glucagon. J Clin Invest 63:525-531, 1979.
  5. Radziuk J, Norwich KH and Vranic M. Experimental validation of measurements of glucose turnover in nonsteady state. Am J Physiol 234: E84-E93, 1978.
  6. Vranic M, Morita S and Steiner G. Insulin resistance in obesity analyzed by the response of glucose kinetics to glucagon infusion. Diabetes 29:169-176, 1980.
  7. Finegood DT, Bergman RN and Vranic M. Estimation of endogenous glucose production during hyperinsulinemic euglycemic glucose clamps: Comparison of unlabeled and labeled exogenous glucose infusates. Diabetes 36:914-924, 1987.
  8. Cherrington AD and Vranic M. Effect of arginine on glucose turnover and plasma free acids in normal dogs. Diabetes 22:537-543, 1973.
  9. Kemmer FW, Sirek A, Sirek OV, Perez G and Vranic M. Glucoregulatory mechanisms following hypophysectomy in diabetic dogs with residual insulin secretion. Diabetes 32:26-34, 1983.
  10. Vranic M and Wrenshall G. Exercise, insulin and glucose turnover in dogs. Endocrinol:85:165-71, 1969.
  11. Vranic M, Kawamori R, Pek S, Kovacevic N and Wrenshall GA. The essentiality of insulin and the role of glucagon in regulating glucose turnover during strenuous exercise. J Clin Invest 57:245-255, 1975.
  12. Kawamori R and Vranic M. Mechanisms of exercise-induced hypoglycemia in depancreatized dogs maintained on long-acting insulin. J Clin Invest 59:331-337, 1977.
  13. Berger M, Halban PA, Muller WA, Offord RE, Renold A and Vranic M. Mobilization of subcutaneously injected tritiated insulin in rats: effect of muscular exercise. Diabetologia 15:113-40, 1978.
  14. Zinman B, Murray FT, Vranic M, Albisser M, Leibel BS, McLean PA and Marliss E. Glucoregulation during moderate exercise in insulin treated diabeti8cs J Clin Endocrinol Metab 45:641-652, 1977.
  15. Challis RAJ, Vranic M and Rada GK. Bioenergetic changes during contraction and recovery in diabetic rat skeletal muscle. Am J Physiol. 256:E129-E137, 1989.
  16. Issekutz B and Vranic M. Role of glucagon in the regulation of glucose production in exercising dogs. Am J Physiol 238:E13-E20, 1980.
  17. Wasserman DH, Lickley HLA and Vranic M. Interactions between glucagon and other counterregulatory hormones during normoglycemic and hypoglycemic exercise in dogs. J Clin Invest 74:1404-1413, 1984.
  18. Wasserman DH, Lickley HLA and Vranic M. Important role of glucagon during exercise in diabetic dogs. J Appl Physiol 59:1272-1281, 1985.
  19. Vranic, M. and Berger, M. Exercise and diabetes mellitus. Editorial. Diabetes 28:147-167, 1979.
  20. Dimitrakoudis D, Ramlal T, Rastogi S, Vranic M and Klip A. Glycemia regulates the glucose transporter number in the plasma membrane of rat skeletal muscle. Biochem J 284:341-348, 1992.
  21. Tsakiridis T, Vranic M and Klip A. Disassembly of the actin network inhibits insulin-dependent stimulation of glucose transport and prevents recruitment of glucose transporters in plasma membrane. J Biol Chem 269:29934-42, 1994.
  22. Tsakiridis T, Vranic M and Klip A. Phosphatidylinositol 3-kinase and the actin network are not required for the stimulation of glucose transport caused by uncoupling the oxidative chain: Comparison with insulin action. Biochem J 309:1-5, 1995.
  23. Marliss EB and Vranic M. Intense exercise has unique effects on both insulin release and its role in glucoregulation: Implications for diabetes. Diabetes 51:S271-283, 2002.
  24. Vranic M and Berger M. Exercise and diabetes mellitus. Editorial. Diabetes 28:147-167, 1979.
  25. Wasserman D, Shi, ZQ and Vranic, M. Metabolic implications of exercise and physical fitness in physiology and diabetes. Ch. 27 In: Ellenberg and Rifkin's Diabetes Mellitus, 5th Edition (D.Porte and R. Sherwin, eds.). Appleton and Lange, Norwalk, USA, pp. 453-480, 2002.
  26. Giacca A, Fisher S, Gupta R, Shi ZQ, Lickley L and Vranic M. Importance of peripheral mechanisms of insulin action for regulation of hepatic glucose production in diabetes. J Clin Invest 90:1769-77, 1992.
  27. Lewis G, Vranic M and Giacca A. Role of combined effects of free fatty acids and glucagon in extra-pancreatic effect of insulin on hepatic glucose production in humans. Am J Physiol 275:E177-186, 1998.
  28. Lewis GH, Carpentier A, Vranic M and Giacca A. Resistance to insulin's direct hepatic effect in suppressing steady state glucose production with type 2 diabetes mellitus. Diabetes 48:570-76, 1999.
  29. Miles P, Yamatani K, Lickley L and Vranic M. Mechanism of glucoregulatory responses to stress and their deficiency in diabetes. Proc Natl Acad Sci USA, 88:1296-1300, 1991.
  30. Lekas M, Fisher S, Van Delangeryt M, Vranic M and Shi ZQ. Glucose uptake during stress is enhanced by β-blockade and not mediated by insulin. J Appl Physiol 87:722-731, 1999.
  31. Rashid S, Shi ZQ, Niwa M, Mathoo JMR, Van Derlangeryt M, Bilinshi D, Lewis G and Vranic M Beta-blockade but not normoglycemia nor hyperinsulinemia markedly diminished stress-induced hyperglycemia in diabetic dogs. Diabetes 49:253-262, 2000.
  32. Fisher SJ, Lekas M, Shi ZQ, Bilinshi D, Carvalho G, Giacca A and Vranic M. Insulin-independent acute restoration of euglycemia normalizes the impaired glucose clearance during exercise in diabetic dogs. Diabetes 46:1805-1812, 1997.
  33. Sigal R, Purdon C, Fisher S, Halter JB, Vranic M and Marliss EB. Hyperinsulinemia prevents prolonged hyperglycemia by correcting glucose metabolic clearance following intense exercise in insulin-dependent diabetic subjects. J Clin Endocrinol Metab 79:1049-1057, 1994.
  34. Efendic S, Wajngot A and Vranic M. Increased activity of the glucose cycle in the liver: early characteristic of type 2 diabetes. Proc Natl Acad Sci USA 82:2965-2969, 1985.
  35. Efendic S, Karlander S and Vranic M. Mild type 2 diabetes markedly increases glucose cycling in the postabsorptive state and during glucose infusion irrespective of obesity. J Clin Invest 81:1953-61, 1988.
  36. Shi ZQ, Giacca A, Fisher S, Vidal H, van der Werve G and Vranic M. Importance of substrate changes in the decrease of hepatic glucose cycling during insulin infusion and declining glycemia in the depancreatized dog. Diabetes 43:1284-1290, 1994.
  37. Rastogi S, Lickley L, Jokay M, Efendic S and Vranic M. Paradoxical reducation in pancreatic glucagon with normalization of somatostatin and decrease in insulin in normoglycemic alloxan-diabetic dogs: a putative mechanism of glucagon irresponsiveness to hypoglycemia. Endocrinol 126:1096-1104, 1990.
  38. Shi ZQ, Rastogi KS, Lekas M, Efendic S, Drucker DJ and Vranic M. Glucagon response to hypoglycemia is improved by insulin-independent restoration of normoglycemia in diabetic rats. Endocrinol 137:3193-3199, 1996.
  39. Chan O, Chan S, Inouye K, Shum K, Bilinski D, Matthews S and Vranic M. Diabetes impairs hypothalamic-pituitary-adrenal (HPA) responses to hypoglycemia and insulin treatment normalizes HPA, but not epinephrine responses. Diabetes 51:1681-1689, 2002.
  40. Inouye K, Shum K, Chan O, Mathoo J, Matthews S and Vranic M. Effects of recurrent hyperinsulinemia with and without hypoglycemia on counterregulation in diabetic rats. Am J Physiol Endocrinol 282: E1369-E1379, 2002.
  41. Kiraly MA, Bates HE, Kaniuk N, Yue JTY, Brummel J, Matthews SG, Riddell MC, Vranic M. Swim training prevents hyperglycemia in ZDF rats: Mechanisms involved in partial maintenance of beta-cell function. Am J Physiol Endocrinol Metab, 2008. Published article online: 20-Nov-2007; doi: 10.1152/ajpendo.00476.2007
  42. Bates HE, Sirek AS, Kiraly MA, Yue JTY, Goche Montes D, Matthews SG, Vranic M. Adaptation to mild, intermittent stress delays development of hyperglycemia in the ZDF rat independent of food intake: role of habituation of the HPA axis, 2008. Endocrinology (in revision) 

Conference Proceedings and Books Edited:

  1. M. Vranic. Tracer methodology and glucose turnover.Fed. Proc. 1837-1876, 1974.
  2. M. Vranic. Turnover of free fatty acids and triglyceride. Fed. Proc. 2233-2270, 1975.
  3. C.F. Ramberg and M. Vranic. Glucose recycling and gluconeogenesis. Fed. Proc. 225-270, 1977.
  4. M. Vranic, J. Wahren and S. Horvath. Proceedings of a conference on diabetes and exercise. Diabetes 28, Suppl. 1, pp. 1-113, 1979.
  5. M. Vranic, G. Steiner and C.H. Hollenberg. Comparison between Type I and Type II diabetes: Similarities and dissimilarities in etiology, pathogenesis and complications. Advances in Experimental Medicine and Biology, vol. 189. Plenum Press, New York, 1985.
  6. A. Tiengo, K.G.M.M. Alberti, S. Del Prato and M. Vranic. Diabetes Secondary to Pancreatopathy: Proceedings of the Post EASD International Symposium on Diabetes Secondary to Pancreatopathy, Padova, Italy, 21-22 September 1987. Excerpta Medica-Elsevier, Amsterdam, 1988.
  7. Vranic, M., C. Hollenberg and S. Efendic. Fuel Homeostasis and The Nervous System. Advances in Experimental Medicine and Biology, vol. 291. Plenum Press, New York and London, 1991.
  8. J.T. Devlin, E.S. Horton, and M. Vranic. Diabetes Mellitus and Exercise. Smith Gordon, London, England, 1992.
  9. Ostenson, C.-G., Efendic, S., Vranic, M. New concepts in the pathogenesis of NIDDM. Advances in Experimental Medicine and Biology, vol. 334. Plenum Press, , 1993.
  10. R. Kawamori, M. Vranic, E. Horton and M. Kubota. Glucose Fluxes, Exercise and Diabetes. Satellite Symposium of 15th IDF Congress, Nara, Japan. Smith-Gordon Co. Ltd., London, 1996.


In the January issue of Nacional Paper in Zagreb, Mladen was included into the list of most cited Diaspora Croatian scientist with 7500 citations.

This biography of Professor Mladen Vranić has been published in the following monograph:

Istaknuti hrvatski znanstvenici u Americi  =  Distinguished Croatian Scientists in America / editor Janko Herak, Zagreb: Hrvatsko-američko društvo, Hrvatska matica iseljenika , 1997

We express our deep gratitude to Professor Janko Herak and to the Croatian - American Society in Zagreb for permission to present this text for the readers of CROWN.

Also many thanks to Professor Mladen Vranić for providing some biographical supplements concerning his work in the period of 1997-2007.

Mladen Vranic to be inducted in the Canadian Medical Hall of Fame in 2009.

Formated for CROWN by prof.dr. Darko Žubrinić
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