histamine his·ta·mine (hĭs'tə-mēn', -mĭn)
A physiologically active depressor amine found in plant and animal tissue, derived from histidine by decarboxylation and released from cells in the immune system as part of an allergic reaction. It is a powerful stimulant of gastric secretion, constrictor of bronchial smooth muscle, and vasodilator.
An organic compound found widely in animals and plants that in humans and other mammals is released as part of the body's immune response, causing physiological changes including dilation of the blood vessels, contraction of smooth muscle (as in the airways), and increased gastric acid secretion. The itching and sneezing typical of respiratory allergies are caused by the release of histamine. Chemical formula: C5H9N3