an amine, CHN, produced by the decarboxylation of histidine and found in all organic matter: it is released by the tissues in allergic reactions, lowers the blood pressure by dilating blood vessels, stimulates gastric secretion, etc.
A physiologically active amine, C5H9N3, found in plant and animal tissue and released from mast cells as part of an allergic reaction in humans. It stimulates gastric secretion and causes dilation of capillaries, constriction of bronchial smooth muscle, and decreased blood pressure.