EFFECTS OF SUBSTANCE-P ON GASTRIC-MOTILITY DIFFER DEPENDING ON THE SITES AND VAGAL INNERVATION IN CONSCIOUS DOGS

The effect of substance P on gastric motility was studied in conscious dogs by means of strain gauge force transducers chronically implanted on the gastric body, antrum, and a vagally-denervated fundic pouch. I ntravenous infusion of substance P in the interdigestive state induced phasic contractions in the pouch and antrum. Atropine inhibited these contractions in the pouch and antrum. Hexamethonium enhanced substanc e P-induced contractions in the gastric antrum, but reduced those in t he pouch. Pretreatment with phentolamine, propranolol, or naloxone did not affect substance P-induced contractions in the pouch and antrum. The intact gastric body scarcely reacted to substance P. Mean systemic blood pressure was lowered by substance P-infusion, but there was no dose-dependency in the reduction of the blood pressure, nor was it aff ected by the pretreatment with atropine or hexamethonium. These result s suggest that 1) the vagal innervation influences the effect of subst ance P on motility in the gastric body, and that 2) substance P may st imulate postsynaptic excitatory cholinergic and presynaptic inhibitory neurons simultaneously in the gastric antrum.