Histamine

Histamine or histamin is an organic nitrogenous compound found in mammals and many vegetables, fruits and food products. It consists of an imidazole ring attached to an ethylamine chain; under physiological conditions, the amino group of the side-chain is protonated. In mammals it is found within granules of basophils and mast cells (over 90% of body stores), as well as within neurons of the tuberomammillary nucleus in posterior hypothalamus. Discovered in 1910, histamine has been considered a local hormone (autocoid) because it is produced without involvement of the classic endocrine glands; however, in recent years, histamine has been recognized as a central neurotransmitter. In humans it is involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Histamine is involved in the inflammatory response and is a central mediator of itching. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.