Effects of metopimazine on gastro-intestinal and biliary tract smooth muscle in vitro

The effects of the phenothiazine derivative metopimazine on the spontaneous or induced activities of guinea-pig isolated stomach and of the rabbit biliary and intestinal tracts were studied. A predominant inhibitory effect was observed except for the circular muscle layers of the duodenum and colon where activation appeared. Evidence from in vitro experiments suggest that metopimazine exerts an inhibitory action partly through a direct effect on smooth muscle cells and partly by reducing stimulated acetylcholine release (at least in the stomach). Finally the involvement of a non-adrenergic, non-cholinergic inhibitory system is postulated.