The role of histamine in allergic diseases.

Histamine, which is stored mainly in mast cells and basophils, is a prominent contributor to allergic disease. Elevations in plasma or tissue histamine levels have been noted during anaphylaxis and experimental allergic responses of the skin, nose, and airways. Of the four cardinal signs of asthma (bronchospasm, edema, inflammation, and mucus secretion), histamine is capable of mediating the first two through its H1 receptor and mucus secretion through its H2 receptor. Of the five cardinal signs of allergic rhinitis (pruritus, mucosal edema, sneezing, mucus secretion, and late-phase inflammatory reactions), histamine is capable of mediating the first three through its H1 receptor. In the nose, mucus secretion can be reflexively mediated by H1 and possibly also by H2 receptors. In the skin the cardinal features of urticaria (vasodilation, vascular permeability, and pruritus) can be mediated by stimulation of the H1 receptor. In anaphylaxis histamine H1-receptor stimulation can mediate vascular permeability, smooth muscle contraction, and tachycardia, whereas H2-receptor stimulation can mediate mucus secretion. Stimulation of both receptors can mediate vasodilation and reduce peripheral vascular resistance. Thus although histamine is only one of many mediators of allergic disease, it plays a primary role in allergic rhinitis, urticaria, anaphylaxis, and to a lesser degree, asthma.