[Histamine and its role in peptic gastric diseases: the discovery of histamine-H2-receptor antagonists].

For the definition of histamine receptors the following prerequisites must be fulfilled: (1) Course of dose-response curves according to the mass-action law; (2) parallel displacement of these curves to the right in the presence of antagonists; (3) inhibition only by specific histamine antagonists; (4) slope of a Schild-plot not significantly different from unity. For H2-receptors these prerequisites could ideally be fulfilled, especially by the development of highly specific H2-receptor antagonists. However, this new class of compounds acts not only by mere competitive inhibition of histamine at its H2-receptor, but also by activating the metabolism of this secretagogue. A further explanation of the action of H2-receptor antagonists in the treatment of chronic duodenal ulcer may be given by studying the pathogenetic role played by histamine in the development of this disease: duodenal ulcer patients showed an increased liberation of histamine from mucosal mast cell stores as well as a decreased activity of histamine methyltransferase (i. e. longer action of histamine!). The rise in histamine content and histamine methyltransferase activity after vagotomy may be the basis for a biochemical explanation of the acid-reducing effect of this operation.