Gastric acid response to topical or intravenous histamine and topical H2-receptor blockade in dogs.

This study was undertaken to determine gastric acid surface and to examine the local effect f ranitidine, a histamine H2-receptor antagonist, on the gastric acid response to histamine. Histamine applied to the Heidenhain pouch (HP) mucosa resulted in a slight and dose-dependent stimulation of acid secretion without affecting acid secretion from the main stomach. Ranitidine given into the HP caused dose-dependent inhibition of the HP response to topical or intravenous histamine without affecting the acid response of the main stomach and without any significant change in the serum ranitidine level. Ranitidine applied to the main stomach with the pylorus occluded inhibited histamine-induced acid secretion also without any increase in the serum ranitidine level. This inhibition was about 30% of that obtained with the same dose of ranitidine given into the stomach with the pylorus left open during the experiment. This study provides evidence that topical histamine is a weak stimulant of gastric secretion and that topical ranitidine is capable of local inhibition of the acid response to both topical and intravenous histamine.