A number of polypeptidic hormones, mainly expressed in the intestine or the pancreas, belong to a group of these structurally related peptides. One such hormone, glucagon, is widely distributed and produced in the alpha-cells of pancreatic islets. It affects glucose metabolism in the liver by inhibiting glycogen synthesis, stimulating glycogenolysis and enchancing gluconeogenesis. It also increases mobilisation of glucose, free fatty acids and ketone bodies, which are metabolites produced in excess in diabetes mellitus. Glucagon is produced, like other peptide hormones, as part of a larger precursor (preproglucagon), which is cleaved to produce glucagon, glucagon-like protein I, glucagon-like protein II, and glicentin. The structure of glucagon itself is fully conserved in all mammalian species in which it has been studied. Other members of the structurally similar group include secretin, gastric inhibitory peptide, vasoactive intestinal peptide (VIP), prealbumin, peptide HI-27 and growth hormone releasing factor.

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