Histamine.

Histamine is a potent mediator of immediate hypersensitivity reactions, and is stored primarily in mast cells and basophils. It exerts its pharmacologic effects through interactions with H1 and H2 cell surface receptors, which promote changes in vascular permeability, levels of cyclic nucleotides, neutrophil and eosinophil chemokinesis and chemotaxis, gastrointestinal secretion, and smooth muscle contraction. H1 and H2 antihistamines have been utilized to interfere with these responses and have proven clinically useful in the treatment of some types of rhinoconjunctivitis, urticaria, and peptic ulcer disease. Several types of biochemical assays have been developed to assess histamine release from mast cells and basophils as well as to measure blood, urine, and tissue levels of histamine. The guinea pig ileum bioassay, fluorometric assay, and radioenzyme assay, each with certain modifications and limitations, have provided useful information concerning the function of histamine in health and disease.