Glucagon
Glucagon is a a 29
amino acid polypeptide acting as an important
hormone in
carbohydrate metabolism. The polypeptide has a
molecular weight of 3485 daltons and was discovered in
1923 by Kimball and Murlin.
Its
primary structure is:
- NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-COOH
History
\nIn the 1920s, Kimball and Murlin studied panreatic extracts and found a additional substance with hyperglycemic properties. Glucagon was sequenced in the late 1950s, but a more complete understanding of its role in physiology and disease was not established until 1970s when a specific radioimmunoassay was developed.
Physiology
\nThe hormone is synthesized and secreted from alpha cells of pancreatic islets (Islets of Langerhans).\n
Glucagon maintains the level of glucose in the blood by binding to specific receptors on hepatocytes causing the liver to release its intracellular stores of glucose. As these stores (in the form of glycogen) become depleted, glucagon then encourages the liver to synthesize glucose by gluconeogenesis. This glucose is released into the bloodstream. Both theses mechanisms leading to glucose release by liver prevent the development of hypoglycaemia.
Pathology
\nAbnormally elevated levels of glucagon may be caused by pancreatic cancers such as glucagonoma, symptoms of which include diabetes mellitus and necrolytic migratory erythema (NME).
Pharmacological application of glucagon
\nAn injectable form of glucagon is essential first aid in cases of\nsevere hypoglycemia. The glucagon is injected and quickly raises blood glucose levels. It works only if there is glycogen stored in liver cells, and it won't work again until those stores are replenished.
Glucagon has also inotropic properties. Although its use is impracticable in heart failure, it has some value in treatmeant of myocardium depression secondary to betablocker overdose.
See also
\n* insulin\n* diabetes mellitus
Category:Peptide hormones
