Effect of morphine sulfate on intestinal transit and myoelectric activity of the small intestine of the rat.

A study was designed to determine the effects of morphine sulfate on small intestinal propulsion and small intestinal myoelectric activity in conscious rats. Adult male rats were divided into two groups. Each member of one group was implanted with an indwelling catheter in the proximal duodenum. Each member of the other group was implanted with electrodes on the serosal surface of the proximal small bowel. Intestinal transit was determined by administering a bolus of radioactive chromium (Na2 51CrO4, 0.5 muCi) in 0.2 ml of saline via the catheter and following its progression through the small intestine. In fasted rats, morphine sulfate administered s.c. inhibited intestinal transit of 51Cr in a dose-dependent manner between 1 and 25 mg/kg. Intestinal motility was determined by monitoring intestinal myoelectric activity both before and after administration of morphine sulfate. In fasted rats, s.c. administration of morphine caused an inhibition of spike potential activity. The inhibition was dose-dependent between dosages of 1 and 25 kg/kg. We conclude that morphine sulfate causes a dose-dependent inhibition of intestinal transit in fasted rats and that this inhibition is correlated with a dose-dependent inhibition of spike potentials of the intestinal smooth muscle cells.