PYY (the acronym PYY is derived from the IUPAC classification of amino acids, in which tyrosine is designated Y) is a thirty-six amino-acid peptide secreted by endocrine cells of the lower small intestinal and colonic mucosa, particularly of the rectum. Its distribution is similar to enteroglucagon, and in some areas, the two peptides are co-localised.
In mammals, PYY delays gastric emptying, decreases intestinal motility, and inhibits secretion of gastric acid. It also inhibits secretion of pancreatic exocrine juices and intestinal hormones, but probably at nonphysiological concentrations. There is a steep rise in PYY secretion after meals, particularly in response to carbohydrates and long-chain fatty acids, and PYY appears, by slowing intestinal transit, to allow more time for absorption. Its release occurs before nutrients have reached the ileum and so may result from a neuroendocrine reflex.
