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The islet of Langerhans plays a key role in glucose homeostasis through regulated secretion of the hormones insulin and glucagon. Islet research has focused on the insulin-secreting β-cells, even though aberrant glucagon secretion from α-cells also contributes to the aetiology of diabetes. Despite its importance, the mechanisms controlling glucagon secretion remain controversial. Proper α-cell function requires the islet milieu, where β- and δ-cells drive and constrain α-cell dynamics. The response of glucagon to glucose is similar between isolated islets and that measured in vivo, so it appears that the glucose dependence requires only islet-intrinsic factors and not input from blood flow or the nervous system. Elevated intracellular free Ca is needed for α-cell exocytosis, but interpreting Ca data is tricky since it is heterogeneous among α-cells at all physiological glucose levels. Total Ca activity in α-cells increases slightly with glucose, so Ca may serve a permissive, rather than regulatory, role in glucagon secretion. On the other hand, cAMP is a more promising candidate for controlling glucagon secretion and is itself driven by paracrine signalling from β- and δ-cells. Another pathway, juxtacrine signalling through the α-cell EphA receptors, stimulated by β-cell ephrin ligands, leads to a tonic inhibition of glucagon secretion. We discuss potential combinations of Ca , cAMP, paracrine and juxtacrine factors in the regulation of glucagon secretion, focusing on recent data in the literature that might unify the field towards a quantitative understanding of α-cell function.
This article was published in the following journal.
Name: Diabetes, obesity & metabolism
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A pancreatic beta-cell hormone that is co-secreted with INSULIN. It displays an anorectic effect on nutrient metabolism by inhibiting gastric acid secretion, gastric emptying and postprandial GLUCAGON secretion. Islet amyloid polypeptide can fold into AMYLOID FIBRILS that have been found as a major constituent of pancreatic AMYLOID DEPOSITS.
A type of pancreatic cell representing about 5-20% of the islet cells. Alpha cells secrete GLUCAGON.
Compounds that supress the degradation of INCRETINS by blocking the action of DIPEPTIDYL-PEPTIDASE IV. This helps to correct the defective INSULIN and GLUCAGON secretion characteristic of TYPE 2 DIABETES MELLITUS by stimulating insulin secretion and suppressing glucagon release.
A 29-amino acid pancreatic peptide derived from proglucagon which is also the precursor of intestinal GLUCAGON-LIKE PEPTIDES. Glucagon is secreted by PANCREATIC ALPHA CELLS and plays an important role in regulation of BLOOD GLUCOSE concentration, ketone metabolism, and several other biochemical and physiological processes. (From Gilman et al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed, p1511)
Peptides derived from proglucagon which is also the precursor of pancreatic GLUCAGON. Despite expression of proglucagon in multiple tissues, the major production site of glucagon-like peptides (GLPs) is the INTESTINAL L CELLS. GLPs include glucagon-like peptide 1, glucagon-like peptide 2, and the various truncated forms.
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