Effect of cimetidine on histamine-stimulated gastric acid and electrolytes in dogs.

Abstract

Intravenous administration of cimetidine (0.25-2.0 mg X kg-1 X h-1) inhibited histamine-stimulated gastric acid secretion in both intact (Ki = 1.0 mg X kg-1 X h-1) and vagotomized (Ki = 1.75 mg X kg-1 X h-1) dogs. During histamine infusion, all doses of cimetidine reduced gastric volume output; high doses increased gastric juice pepsin and [Na+] and reduced [H+] and [Cl-]. Gastric juice [K+] was not affected during cimetidine infusion. The cimetidine-induced changes in electrolyte concentrations were qualitatively comparable with those observed on withdrawal of histamine stimulation. On termination of cimetidine infusion with continued histamine administration, gastric [K+] and volume output increased immediately, followed 30 min later by an increase in [H+] and a reciprocal decrease in [Na+]; [Cl-] did not recover. The changes in gastric juice electrolytes after termination of cimetidine, with the exception of [Cl-], mimicked the changes observed on initiation of histamine stimulation. These data indicate that the effects of cimetidine may be totally explained by its antagonism of histamine binding to the parietal cell H2-receptor, that vagotomy reduces cimetidine binding to the H2-receptor, and that cimetidine antagonism of histamine is rapidly reversed on removal of the antagonist.