The Human Body

Histamine

Histamine, also histamine phosphate, an amine (beta-imidazolyl-ethylamine, ergamine, or ergotidime) that is a normal constituent of almost all animal body cells.

Histamine is also found in minute quantities in ergot and putrefied meat products and is produced synthetically for medicinal purposes. In the body, it is synthesized in a type of leukocyte (see Blood) called a basophil or mast cell. In response to certain stimuli these cells release histamine, which immediately effects a dilation of the blood vessels. This dilation is accompanied by a lowering of blood pressure and an increased permeability of the vessel walls, so that fluids escape into the surrounding tissues. This reaction may result in a general depletion of vascular fluids, causing a condition known as histamine poisoning or histamine shock. Allergic reactions in which histamine is released, resulting in the swelling of body tissue, show similarities to histamine poisoning; the two may be basically allied, and the two conditions are treated similarly. The release of histamine might also be partly responsible for difficult breathing during an asthma attack.

Histamine also causes contraction of involuntary muscles, especially of the genital tract and gastrointestinal canal, with an accompanying secretion by associated glands. Because histamine stimulates the flow of gastric juices, it is used diagnostically in patients with gastric disturbances. One drug effective in treating gastric ulcers acts by antagonizing the action of histamine. The ability of the body to localize infections may be due to the secretion of histamine and the subsequent increased local blood supply and increased permeability of the blood vessels.