Is dopamine an inhibitory modulator of gastrointestinal motility?

The effects of dopamine were studied on the isolated guinea-pig stomach preparation, including the duodenal bulb. Phasic activity: intra-arterially administered dopamine (0.25 mg/l) reduced phasic activity and blocked antro-duodenal coordination. The selective dopamine-antagonist, domperidone, increased phasic amplitude and improved antro-duodenal coordination. Tonic activity: gastric relaxation induced by equi-active concentrations of dopamine (0.25 mg/l, i.a.) and noradrenaline (0.04 mg/l, i.a.) could be antagonized by domperidone and prazosin; domperidone being more effective against dopamine and prazosin against noradrenaline. Our results support the hypothesis that dopamine acts as an inhibitory neuromodulator. The actions of dopamine in decreasing spontaneous activity and in inducing relaxation could set the stage for duodenal-gastric reflux.