Classification and biological distribution of histamine receptor sub-types

Abstract

The distribution and classification of histamine receptors in mammalian and avian tissues have been summarized in Tables 1–4. It is evident that histamine receptors are present on a number of morphologically distinct cell types and the proportion of cells bearing H₁- and H₂-receptors varies not only with the species but also with the cell source. The pharmacological receptors mediating mepyramine-sensitive histamine responses have been defined as H₁-receptors. Receptors mediating mepyramine-resistant, but burimamide or metiamide-sensitive histamine responses have been classified as H₂-receptors. Histamine responses mediated via H₂-receptors seem to involve the adenylcyclase system resulting in elevation of intracellular cyclic-AMP level, which is susceptible to burimamide blockade but insensitive to β-adrenergic blocking agents. This mode of action of histamine involving H₂-receptors and the adenyl cyclase system has been shown to stimulate the mammalian heart; promote gastric acid secretion; inhibit antigen-induced histamine release from leucocytes and inhibit lymphocyte-mediated cytotoxicity. It can further be concluded that both H₁- and H₂-receptors are widely distributed throughout the animal body in the gastro-intestinal, reproductive, respiratory and cardiovascular systems, nervous system and on mast cells and blood leucocytes. In these tissues, histamine receptors play an important role in physiological, immunological and immunopathological processes. Interaction of histamine with both H₁- and H₂-receptors in varying proportions modulates the overall manifestation of cardiovascular and respiratory syndromes during certain immunopathological conditions (e.g. inflammation, allergy and anaphylaxis). Histamine receptors also appear to play an important role in the development of immuno-competence and immunity.