histamine

[(Science: biochemistry) formed by decarboxylation of histidine. potent pharmacological agent acting through receptors in smooth muscle and in secretory systems. stored in mast cells and released by antigen. (see hypersensitivity). Responsible for the early symptoms of anaphylaxis. also present in some venoms. amine formed from histidine that stimulates gastric secretions and dilates blood vessels; released by the humane immune system during allergic reactions.A chemical that is produced particularly by leucocytes that results in blood vessels becoming more permeable and in turn lose fluid to the tissues. this can result in localised swelling, and is a direct response to the presence of an [[antigen.

[1. A vasodepressor amine derived from histidine by histidine decarboxylase and present in ergot and in animal tissues. It is a powerful stimulant of gastric secretion, a constrictor of bronchial smooth muscle, and a vasodilator (capillaries and arterioles) that causes a fall in blood pressure. Histamine, or a substance indistinguishable in action from it, is liberated in the skin as a result of injury. When injected intradermally in high dilution, it causes the triple response.