glucagon

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glucagon

(glo͞o`kəgŏn), hormonehormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
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 secreted by the α cells of the islets of Langerhans, specific groups of cells in the pancreaspancreas
, glandular organ that secretes digestive enzymes and hormones. In humans, the pancreas is a yellowish organ about 7 in. (17.8 cm) long and 1.5 in. (3.8 cm) wide. It lies beneath the stomach and is connected to the small intestine at the duodenum (see digestive system).
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. It tends to counteract the action of insulininsulin,
hormone secreted by the β cells of the islets of Langerhans, specific groups of cells in the pancreas. Insufficiency of insulin in the body results in diabetes. Insulin was one of the first products to be manufactured using genetic engineering.
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, 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 peptidepeptide,
organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid.
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) was published in 1956–57. One of the most important actions of glucagon is the promotion of glycogenolysis, i.e., the degradation of glycogenglycogen
, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose.
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 to glucose, in the liver. Glucagon stimulates adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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 to 3′5′-cyclic adenosine monophosphateadenosine monophosphate
(AMP) , organic compound composed of an adenine base, the sugar ribose, and one phosphate unit. AMP is one of the possible products of the hydrolysis of adenosine triphosphate (ATP) and is therefore important in the transfer of chemical energy during
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 (cyclic AMP).

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

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.
References in periodicals archive ?
Therefore, in this study, mRNA level of PEPCK-C in the liver of ketotic dairy cows did not decrease but increased (Table 4), which might be related to the hypoinsulinemia and low ratio of insulin to glucagons.
In this study, the increase of PEPCK-C mRNA level in the liver of ketotic cows was in favor of the augmentation of hepatic gluconeogenesis and relief of negative energy balance, but the decreased concentration of glucagons and the increased concentration of NEFA and BHBA in plasma of the diseased cows meant that the above adaptive changes were still insufficient to correct the metabolic confusion of ketosis.
For the study, the researchers studied the hormone glucagon, which raises blood sugar levels to fuel activity.
Located in the pancreas, they produce glucagon, a hormone released during fasting, to tell the liver to make glucose for use by the brain.
Thus glucagon and insulin are part of a feedback system designed to keep blood glucose at a stable level.
The results of our studies indicated that infusion of galanin into the third ventricle may increase the plasma levels of GH, glucagons, fatty acid and urea, and decrease the plasma levels of T3, T4, insulin and glucose in goats undergoing severe body loss.
Effect of galanin on plasma glucose, insulin and pancreatic glucagon in dogs.
Studies in healthy volunteers suggest that glucagon and other hormonal counterregulatory response to hypoglycemia were preserved with short-term administration of exenatide.
In addition, GLP-1 stimulates insulin synthesis, inhibits glucagon secretion, delays gastric emptying, and may promote satiety.
Thus, although most studies on the developmental effects of CPF are appropriately directed toward neurotoxicity, the present work instead takes a similar approach with regard to cell signaling in the liver and heart, concentrating on the cAMP cascade and its responses to some of the major inputs that control that pathway, [beta]-adrenoceptors ([beta]ARs), and glucagon receptors (Figure 1).