A chemical that is present in cells (mainly mast cells) throughout the body that is released during an allergic reaction (see allergy). Histamine activates 2 main types of receptors, H1 and H2. H1 activation is responsible for the swelling and redness that occur in inflammation. It also narrows the airways in the lungs and causes itching. H2 activation stimulates acid production by the stomach. These effects can be counteracted by antihistamine drugs.
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The defense substance responsible for most inflammation. It is synthesized from the amino acid histidine and is secreted by mast cells, basophils, and blood platelets. It stimulates vasodilation, capillary permeability, muscle contraction of the bronchioles, secretions of a number of glands, and attracts eosinophils, the white blood cells that are capable of moderating the inflammation. Mast cell histamine release is what usually causes allergies.
An amine (see AMINES) derived from HISTIDINE. It is widely distributed in the tissues of plants and animals, including humans. It is a powerful stimulant of gastric juice, a constrictor of smooth muscle including that of the bronchi, and a dilator of arterioles and capillaries. It is this last action which is responsible for the eruption of URTICARIA.
n. a compound derived from the amino acid histidine. It is found in nearly all tissues of the body, associated mainly with the *mast cells. Histamine has pronounced pharmacological activity, causing dilation of blood vessels and contraction of smooth muscle (for example, in the lungs). It is an important mediator of inflammation and is released in large amounts after skin damage (such as that due to animal venoms and toxins), producing a characteristic skin reaction (consisting of flushing, a flare, and a weal). Histamine is also released in anaphylactic reactions and allergic conditions, including asthma, and gives rise to some of the symptoms of these conditions. See also anaphylaxis; antihistamine.
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