Gastric relaxation induced by peri-arterial (sympathetic?) electrical stimulation in vitro

The aim of this study was to determine the receptor types that mediate the relaxation evoked by electrical stimulation of the peri-arterial nerves (response abolished by tetrodotoxin) innervating the gastroduodenal preparation of the guinea pig. The lack of effect of atropine, prazosin and propranolol suggests that muscarinic, alpha 1- and beta-adrenergic receptor sites are not involved. The electrically stimulated canine saphenous vein was used to determine the order of potency of alpha 2- and dopamine-antagonists on postsynaptic alpha 2-adrenergic receptor sites: yohimbine greater than piperoxan greater than pimozide approximately tolazoline approximately domperidone greater than sulpiride. In contrast their order of potency against peri-arterial nerve stimulation was pimozide approximately yohimbine greater than domperidone greater than piperoxan approximately tolazoline greater than sulpiride, suggesting that the receptor type(s) involved in the relaxation are not only alpha 2-adrenergic receptors. Pretreatment with 6-hydroxydopamine halved the induced gastric relaxation but reduced the splenic norepinephrine content by 90%. These findings together with the efficacy of domperidone and pimozide in inhibiting the relaxation evoked in the guinea pig stomach by peri-arterial nerve stimulation suggests that the evoked relaxation may, at least partly, be mediated via dopamine receptor sites.