Acute effects of morphine on rat intestinal motility

Abstract

Systemic injection of morphine (0.5-16 mg/kg) caused dose-related increases in intestinal intraluminal pressure in anesthetized rats. Injection of morphine into cerebral ventricles was no more effective than the intravenous (i.v.) route. Decapitation of the animals did not prevent the intestinal stimulatory effect of i.v. morphine. The intestinal stimulation induced by i.v. morphine and 5-hydroxytryptamine (5-HT), but not that induced by cholecystokinin octapeptide, was antagonized by methysergide. Morphine appears to stimulate contractions of intestinal circular muscle in the rat by release of local, endogenous 5-HT.