histamine

1. (biochemistry) An amine, C₅H₉N₃, formed by decarboxylation of histidine, that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion; it is released during allergic reactions.Examples: "Mellanby and Twort have isolated from the fæces a bacillus which is able to produce from one of the amino acids normally formed in digestion of proteins a highly active body, histamine."; "The intake of food triggers a release of histamine, which activates the acid-secreting cells."; "In a strongly ripened cheese, the casein proteins are broken down to amino acids, and the amino acids can be broken down into amines, small molecules that can serve as chemical signals in the human body. Histamine and tyramine are found in large quantities in Cheddar, blue, Swiss, and Dutch-style cheeses, and can cause a rise in blood pressure, headaches, and rashes in people who are especially sensitive to them."