Dissociated response of acid and pepsin secretion to omeprazole in an in vitro perfused mouse stomach

Abstract

The effect of omeprazole, an inhibitor of the parietal cell H+-K+-ATPase, on pepsin and acid secretion was studied in an in vitro perfused whole mouse stomach model. Omeprazole inhibited basal and dibutyryl cAMP (DBcAMP)- and histamine-stimulated acid secretion in a dose-dependent fashion with a maximally effective dose of 10(-4) M. At the same time, omeprazole induced a dose-dependent increase of unstimulated pepsin release. This increase was not affected by pretreatment with 10(-3) M atropine or 10(-4) M cimetidine. It was, however, inhibited by preincubation with 10(-4) M carbonyl cyanide m-chlorophenylhydrazone (CCCP). Pepsin secretion after maximally effective doses of histamine or DBcAMP was not affected by 10(-4) M omeprazole. In a concentration of 10(-5) M, the effect of omeprazole was additive to the effect of submaximal concentrations of carbachol and histamine. NaSCN and imidazole mimicked the effect of omeprazole on acid secretion, but pepsin release was only stimulated with 10(-2) M imidazole. Another weak base, benzylamine, stimulated acid and pepsin in parallel. Luminal perfusion with solutions of high K+ concentration did not enhance basal pepsin release. The dissociated response of acid and pepsin secretion indicates that omeprazole does not act selectively on the parietal cell. The stimulation of pepsin secretion might be related to the weak base properties of the compound.