Cisapride counteracts the anticholinergic effect of disopyramide on the guinea pig isolated small but not large intestine.

This study examines the influence of the prokinetic agent cisapride on the disopyramide's effect on the isolated duodenum and ileum, as well as on the ascending colon of the guinea pig. Acetylcholine produced the well known stimulatory effect on the intestinal parts with EC50 values 9.6 x 10(-8), 7 x 10(-9) and 1.1 x 10(-6) M for the duodenum, ileum and ascending colon, respectively. Disopyramide inhibited, in a concentration-dependent manner, the contractile responses of the intestinal parts to acetylcholine. Cisapride, at concentrations ranging from 5 x 10(-9) M to 10(-6) M, significantly reversed the above inhibitory effect of disopyramide on the guinea pig duodenum and ileum and produced a parallel leftward shift of the concentration-response curve for acetylcholine in the presence of disopyramide. However, cisapride was not found able to reverse the inhibitory effect of disopyramide on the ascending colon. In conclusion, cisapride may counteract the inhibitory effect of disopyramide on the guinea pig duodenum and ileum, probably by facilitating the cholinergic neurotransmission, while it is not able to reverse the disopyramide's inhibitory effect on the guinea pig ascending colon.