glucagon

glucagon

glucagon (glo͞oˈkəgŏn), hormone secreted by the α cells of the islets of Langerhans, specific groups of cells in the pancreas. It tends to counteract the action of insulin, i.e., it raises the concentration of glucose in the blood. Glucagon was first purified and crystallized in 1955; the amino acid sequence of this 29-amino acid polypeptide (see peptide) was published in 1956–57. One of the most important actions of glucagon is the promotion of glycogenolysis, i.e., the degradation of glycogen to glucose, in the liver. Glucagon stimulates adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate to 3′5′-cyclic adenosine monophosphate (cyclic AMP).

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Glucagon

The protein hormone secreted by the pancreas which is known to influence a wide variety of metabolic reactions. Glucagon, along with insulin and other hormones, plays a role in the complex and dynamic process of maintaining adequate supplies of sugar in the blood. Glucagon has often been called the hyperglycemic-glycogenolytic factor because it causes the breakdown of liver glycogen to sugar (a process known as glycogenolysis) and thereby increases the concentration of sugar in the bloodstream (a condition known as hyperglycemia). Glucagon may also be involved in the regulation of protein and fat metabolism, gastric acid secretion and gut motility, excretion of electrolytes (such as sodium, potassium and chloride) by the kidney, contractility of heart muscle, and release of insulin from the pancreas. Glucagon is used in human medicine chiefly in certain diabetic conditions when a dangerously low blood sugar must be rapidly raised. See Carbohydrate metabolism, Glycogen, Hormone, Insulin, Pancreas

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

glucagon

[′glü·kə‚gän]

(biochemistry)

The protein hormone secreted by α-cells of the pancreas which plays a role in carbohydrate metabolism. Also known as hyperglycemic factor; hyperglycemic glycogenolytic factor.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.