histamine(redirected from H substance (inflammation))
Also found in: Dictionary, Thesaurus, Medical.
histamine(hĭs`təmēn'), organic compound derived in the body from the amino acid histidinehistidine
, organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
..... Click the link for more information. by the removal of a carboxyl group (COOH). Although found in many plant and animal tissues, histamine is specifically important in human physiology because it is one of the chemicals released from certain cells (particularly mast cells) upon tissue injury or during the neutralization of foreign material (antigens) by certain types of antibodies. Released histamine tends to dilate blood capillaries, often causing the skin to appear red and feel warm, and makes the capillaries more permeable, allowing fluid to escape into the tissues. This causes edema (swelling), usually manifested as acute urticaria (rapidly appearing hives, accompanied by severe itching). This sort of reaction is common to many allergies, such as food allergies, and the symptoms can often be controlled well with antihistaminesantihistamine
, any one of a group of compounds having various chemical structures and characterized by the ability to antagonize the effects of histamine. Their principal use in medicine is in the control of allergies such as hay fever and hives.
..... Click the link for more information. . Unfortunately, histamine is not the only substance released under these conditions, and some allergies, particularly chronic ones such as asthma, are relatively resistant to antihistamine therapy.
A biologically active amine that is formed by the decarboxylation of the amino acid histidine. It is widely distributed in nature and is found in plant and animal tissues as well as in insect venoms. In humans, histamine is a mediator of inflammatory reactions, and it functions as a stimulant of hydrochloric acid secretion in the stomach.
Most tissue histamine is found stored in mast cells, where it can be released by a variety of stimuli. Once released, it can cause many effects, including constriction of bronchiolar, gastrointestinal, uterine smooth muscle, and lowering of blood pressure. If histamine is released in the skin, itching, a flare (area of redness) due to vasodilation, and a wheal due to leaking of fluid into the tissue are observed. The increase in vascular permeability that permits this leakage is due to an action on the endothelial cells of postcapillary venules.
All of these actions of histamine are mediated by the activation of histamine receptors, designated either H-1 or H-2. Antihistamine drugs exert their effects by blocking the combination of histamine with these receptors. See Antihistamine
Histamine release can be caused by tissue injury, by physical stimuli such as cold or pressure, by drugs such as heroin, and most importantly by immunologic mechanisms. Mast cells in the skin, the lung, the nasal passages, or other sites may become sensitized to antigens such as ragweed or other pollens, and then release histamine and other biologically active substances upon exposure to them. The released histamine may then cause the effects commonly associated with allergic responses. If the allergic reaction becomes generalized and severe, life-threatening anaphylactic shock may ensue. The prompt administration of epinephrine, which exerts effects opposite to those of histamine, can be life-saving in such cases. See Allergy, Antigen, Epinephrine, Hypersensitivity, Immunology
[β-imidazole-4(5)-ethylamine], a tissue hormone that is strongly biologically active; one of the biogenic amines. It is formed as a result of the decarboxylation of the amino acid, histidine:
Histamine is contained in large quantities in inactive, bound form in various organs and tissues of animals and humans (lungs, liver, and skin), and also in thrombocytes and leucocytes. It is liberated in cases of anaphylactic shock and inflammatory and allergic reactions. It produces dilation of the capillaries and an increase in their permeability, constriction of the large vessels, contraction of the smooth musculature, and sharp increase of hydrochloric-acid secretion in the stomach. The release of histamine from its bound state during allergic reactions leads to reddening of the skin, itching, burning, and formation of blisters. Histamine decomposes under the action of the enzyme histaminase, mainly in the intestinal tract and the kidneys. Histaminase (diaminoxidase) catalyzes the oxidative deamination of histamine, as a result of which a nontoxic product (imidazole-acetaldehyde) is formed. The enzyme is active only in the presence of oxygen; it may deaminate diamines other than histamine.
E. V. PETUSHKOVA