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.