The Online Encyclopedia and Dictionary







Histamine diagram

Histamine is a monoamine chemical involved in local immune responses.

Chemical properties

Chemically, histamine is 2-(4-imidazolyl)ethylamine and has the formula C5H9N3. Histamine is synthesized by the decarboxylation of the amino acid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase . It is a hydrophilic vasoactive amine (thus the name). Some forms of food poisoning are due to conversion of histidine into histamine in spoiled foodstuffs, such as fish.


Release of histamine is associated with allergic reactions, as it causes both an inflammatory response and a contraction of smooth muscle tissue. Histamine is released by mast cells primarily when they degranulate due to IgE antibodies.

Histamine also regulates stomach acid production. The -amine also may function as a neurotransmitter in the central nervous system.

Histamine mediates its effects via histamine receptors, which are classified into types:

See also

Last updated: 02-08-2005 11:16:41
Last updated: 05-03-2005 17:50:55