Gastrointestinal effects of metoclopramide in man. In vitro experiments with human smooth muscle preparations.

Metoclopramide (N-(diethylaminoethyl)-2-methoxy-4-amino-5-chlorobenzamide) has been investigated with human gastrointestinal smooth-muscle preparations in vitro. Small-intestinal and colonic circular muscle was contracted by metoclopramide. This effect was antagonized by atropine. Gastric and colonic longitudinal muscle was sensitized by metoclopramide to acetylcholine. Atropine acted here as a partial antagonist of metoclopramide.The interference of acetylcholine and metoclopramide is of a hitherto undescribed pharmacological type. The effects of metoclopramide in vivo-where its action is predominantly on the stomach and pylorus-are not fully explained by these in vitro experiments in which the effect was found to be most pronounced on the colon.