The inhibition of acetylcholinesterase by ranitidine: a study on the guinea pig ileum.

The present work was performed to investigate if the stimulating effect of ranitidine on the intestinal smooth muscle is connected with a possible inhibition of the acetylcholinesterase. Isolated segments of guinea pig ileum were used in Tyrode solution at 37 degrees C. The maximum activity of ranitidine on the ileum was about 79% of the maximum activity of acetylcholine and about 90% of the maximum activity of physostigmine. The contractile responses induced by ranitidine were prevented by atropine and this prevention was stronger against physostigmine. Ranitidine produced an augmentation of the acetylcholine induced contractions which was less against physostigmine. The contractile responses induced by acetylcholine were prevented by acetylcholinesterase. This acetylcholinesterase activity was inhibited by ranitidine and this inhibition was weaker than that caused by physostigmine. These findings suggest that ranitidine exerts at least an anticholinesterase activity which is weaker against physostigmine.