Immunology => 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 produced synthetically for medicinal purposes. In the body, it is synthesized in a type of leucocyte (see Blood) called a basophil or mast cell. In response to certain stimuli, such as skin damage caused by venoms and other toxins, these cells release histamine, which immediately effects a dilation of the blood vessels-an inflammatory reaction. 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.
In the 1930s the Italian pharmacologist Daniel Bovet, working at the Pasteur Institute in Paris, discovered that certain chemicals counteracted the effects of histamine in guinea pigs. The first antihistamines were too toxic for use on humans, but by 1942 they had been modified for use in the treatment of allergies. More than 25 antihistamine drugs are now available.
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.