Bernard explores how hormones work by feeding dogs carbohydrates or meat and concluded that liver was storing a water insoluble starchy substance that he named glycogen.
Introduction à l'étude de la médecine expérimentale.
Bernard's study of the pancreas would be discovered by Banting's doctor.
Bernard’s contribution in the study of metabolism and diabetes remains leading. In 19th century, scientists hypothesized on the role of pancreas in the physiopathology of diabetes as they found in the post-mortem examination of the diseased, atrophic or stone filled pancreases. However, as they believed that pancreas was an exocrine organ, they interpreted these post-mortem findings as a chance phenomenon. During that period the French experimental physiologist, Claude Bernard decided to test this hypothesis[1,12].
At the beginning, he falsely believed that “diabetes was a nervous affection of the lungs”. However, during an experiment, he injected grape sugar into the jugular vein of a dog, extracting at the same time blood from the carotid artery. This blood contained a large amount of sugar and he realized that glucose was not destroyed in the lungs, because blood must pass by these organs in order to move from the jugular vein to the carotid artery. He was then fed dogs on a carbohydrate-rich diet, the blood from the hepatic veins and vena cava contained sugar which was not destroyed in the liver and was also present in heart ventricles, so the theory of lungs’ role in diabetes was rejected. In further experiments, Bernard proved that animal blood contains sugar even if it is not supplied by food. Testing the theory that sugar absorbed from food was destroyed when it was passing through tissues, Bernard put dogs in carbohydrate diet and killed them immediately after feeding. To his surprise he observed large amounts of sugar in hepatic veins. The same observation was done in the control group, animals that were fed only by meat. He then moved to the analysis of liver tissue samples and in every liver he examined he found large quantities of glucose which was missing from other organs. He concluded that liver was storing a water insoluble starchy substance that he named glycogen which was converted into sugar or glucose and secreted into the blood. He assumed that it was an excess of this secretion that caused diabetes[13,14].
Moving toward, Bernard demonstrated the connection between the central nervous system and diabetes. Using a needle, he stimulated the floor of the fourth brain ventricle and produced temporary “artificial diabetes” which lasted less than one day. He named this procedure piqûre diabétique and linked for the first time glucose homeostasis and the brain to the pathogenesis of diabetes.