Dopaminergic and beta-adrenergic effects on gastric antral motility.

Stimulation of splanchnic nerves and application of adrenergic drugs have been shown to give variable effects on gastric motor activity depending especially on the background activity. beta-adrenoceptors and dopaminergic receptors mediate inhibitory effect on proximal gastric motor activity. The purpose of the present study was to evaluate the effects of isoprenaline, a beta 1- and beta 2-agonist, and dopamine on gastric antral motility in gastric fistula dogs. Dopamine was used alone and in conjunction with selective blockade of adrenergic and dopaminergic receptors during infusion of bethanechol or pentagastrin inducing motor activity patterns as in the phase III of the MMC and the digestive state respectively. The stimulated antral motility was dose-dependently inhibited by dopamine. The effect was significantly blocked by specifically acting dopaminergic blockers, while alpha- and beta-adrenergic blockers were without any significant effects. Dose-response experiments with bethanechol and dopamine showed inhibition of a non-competitive type. Isoprenaline was used alone and in conjunction with selective blockade of beta 1- and beta 2-receptors during infusion of bethanechol which induces a pattern similar to phase III in the migrating myoelectric complex. The stimulated antral motility was dose-dependently inhibited by isoprenaline. The effect could be significantly blocked by propranolol (beta 1 + beta 2-adrenoceptor blocker) and by using in conjunction the beta 1-adrenoceptor blocker practolol and the beta 2-adrenoceptor blocker H 35/25. The dose-response experiments showed inhibition of a non-competitive type. These studies indicate that gastric antral motility is inhibited by isoprenaline through both beta 1- and beta 2-receptors and by dopamine through specific dopaminergic receptors.