Subcutaneous morphine reduces intestinal propulsion in rats partly by a central action

Rats were given intracerebroventricular or intravenous injections of the quarternary opioid receptor antagonist N,N-diallyl-normorphinium (DANM. 100 microgram). Ten min later morphine (7.5 mg/kg) or loperamide (10 mg/kg) was injected subcutaneously. Intestinal propulsion was assessed by measuring the progress of radioactive chromium (Na51(2) CrO4, 0.5 microCi) along the small intestine. The radioactive chromium was instilled into the proximal duodenum 20 min after injection of morphine or loperamide, and the animals sacrificed 35 min after giving radioactive chromium. Morphine and loperamide both inhibit intestinal propulsion. DANM (100 microgram i.c.v.) reduces the effect of morphine but not loperamide. Intravenous injection of DANM does not reduce anti-propulsive action of morphine. By itself DANM neither increases nor decreases intestinal propulsion. These experiments indicate that morphine, when administered by a peripheral route, reduces small intestinal propulsion in the rat partly through an action on brain opioid receptors.