Cholinergic-like effects of the new histamine H2-receptor antagonist ranitidine

The new H2-receptor blocker ranitidine, together with the effect on histamine H2-receptors, possesses a series of cholinergic-like actions: it provokes atropine-sensitive contractions of several isolated smooth muscle preparations from different animal species and it potentiates the stimulant effect of acetylcholine. Moreover it contracts human lower esophageal sphincter in vivo, an effect which is completely prevented by small doses of atropine. Finally, ranitidine potentiates the stimulant effect of bethanechol and of carbachol on salivary glands of the rat while leaving unaffected the secretagogue effect of physalaemin which is known to be completely independent of the cholinergic system. In the in vivo experiments the doses of ranitidine capable of eliciting cholinergic-like effects were of the same order of magnitude as those necessary to cause the H2-receptor blockade.