Insulin (from Latin insula, "island", as it is produced in the Islets of Langerhans in the pancreas) is a polypeptide hormone that regulates carbohydrate metabolism. Apart from being the primary effector in carbohydrate homeostasis, it also has a substantial effect on small vessel muscle tone, controls storage and release of fat (triglycerides) and cellular uptake of both amino acids and some electrolytes. In this last sense, it has anabolic properties. Its concentration (more or less, presence or absence) has extremely widespread effects throughout the body. more...
Insulin is used medically in some forms of diabetes mellitus. Patients with type 1 diabetes mellitus depend on exogenous insulin (injected subcutaneously) for their survival because of an absolute deficiency of the hormone; patients with type 2 diabetes mellitus have either relatively low insulin production or insulin resistance or both, and a non-trivial fraction of type 2 diabetics eventually require insulin administration when other medications become inadequate in controlling blood glucose levels.
Insulin has the empirical formula C257H383N65O77S6.
Insulin structure varies slightly between species of animal. Its carbohydrate metabolism regulatory function strength in humans also varies. Pig insulin is particularly close to the human one.
Discovery and characterization
In 1869 Paul Langerhans, a medical student in Berlin, was studying the structure of the pancreas under a microscope when he noticed some previously-unidentified cells scattered in the exocrine tissue. The function of the "little heaps of cells," later known as the Islets of Langerhans, was unknown, but Edouard Laguesse later argued that they may produce a secretion that plays a regulatory role in digestion.
In 1889, the Polish-German physician Oscar Minkowski in collaboration with Joseph von Mehring removed the pancreas from a healthy dog to demonstrate this assumed role in digestion. Several days after the dog's pancreas was removed, Minkowski's animal keeper noticed a swarm of flies feeding on the dog's urine. On testing the urine they found that there was sugar in the dog's urine, demonstrating for the first time the relationship between the pancreas and diabetes. In 1901, another major step was taken by Eugene Opie, when he clearly established the link between the Islets of Langerhans and diabetes: Diabetes mellitus.... is caused by destruction of the islets of Langerhans and occurs only when these bodies are in part or wholly destroyed. Before this demonstration, the link between the pancreas and diabetes was clear, but not the specific role of the islets.
Over the next two decades, several attempts were made to isolate the secretion of the islets as a potential treatment. In 1906 Georg Ludwig Zuelzer was partially successful treating dogs with pancreatic extract, but unable to continue his work. Between 1911 and 1912, E.L. Scott at the University of Chicago used aqueous pancreatic extracts and noted a slight diminution of glycosuria, but was unable to convince his director and the research was shut down. Israel Kleiner demonstrated similar effects at Rockefeller University in 1919, but his work was interrupted by World War I and he was unable to return to it. Nicolae Paulescu, a professor of physiology at the Romanian School of Medicine, published similar work in 1921 that was carried out in France and patented in Romania, and it has been argued ever since by Romanians that he is the rightful discoverer.
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