Cisapride inhibits motility of the sphincter of Oddi in the Australian possum.

Cisapride has been shown in a number of recent studies to have prokinetic effects on the gastrointestinal tract. Studies of its action on the biliary tract have been limited. In this study we determined the effect of cisapride on sphincter of Oddi motility of the Australian brush tailed possum in vivo, and evaluated possible mechanisms for its effect. Cisapride produced a dose-dependent inhibition of sphincter of Oddi phasic contractions. The inhibitory effect was not blocked by atropine, phentolamine, propranolol, methysergide, or hexamethonium administration, or after cervical truncal vagotomy. Tetrodotoxin, however, abolished the sphincter response to cisapride. We conclude that cisapride has an inhibitory effect on the possum sphincter of Oddi. This inhibitory effect is mediated via nonadrenergic, noncholinergic inhibitory neurons and is similar to the inhibitory effect of cholecystokinin on the sphincter of Oddi.