Studies on the role of dopamine and dopamine blockers in gastroduodenal motility.

In vitro studies on an intact gastroduodenal preparation of the guinea-pig indicated that dopamine inhibited motor activity via a direct action on the gastrointestinal wall. Dopamine-induced relaxations were prevented by dopamine antagonists, which also exerted intrinsic stimulatory effects and improved gastroduodenal coordination. These effects were confirmed in vivo on conscious dogs. The results cannot be explained by an interaction with alpha- receptors, since alpha-adrenergic blocking concentrations of prazosin were inactive against dopamine, and dopamine-blocking concentrations of domperidone did not interfere with noradrenaline-induced relaxations. Pharmacological evidence confirmed the presence of dopamine receptors in the stomach of conscious dogs. The presence of specific dopamine receptors in the gastrointestinal tract is strongly indicated, and an important role for endogenous dopamine as an inhibitory neuromodulator of gastroduodenal motility is suggested.