Radioautographic Characterization of H1 and H2 Receptor Antagonists

Histamine is thought to be one of the most important neuromodulators in the gastric mucosa, participating mainly in the regulation of hydrochloric acid secretion and blood flow. Pharmacological studies revealed that the action of histamine is mediated by two types of receptors: H1 and non-H1 receptors, i.e., H2 receptors. The existence of non-H1 receptors was initially revealed through evidence that certain effects of histamine, such as gastric acid secretion and cardiac chronotropism, are not antagonized by typical antihistamines.1 The important derivation of a second class of histamine antagonists2 defined this new class of receptors, the H2 receptors, as being those which are unaffected by classical H2 antihistamines like pyrilamine. The subsequent phenomenal success of this new H2 receptor antagonist, Cimetidine, in treating duodenal ulcers by suppression of acid secretion has confirmed the functional significance of histamine in the gastric mucosa.