title: Myoelectric activity of the small intestine during morphine dependence and withdrawal in rats.
abstract: We investigated the effect of morphine dependence on the migrating myoelectric complex (MMC) of the small intestine, whether bacterial overgrowth developed in morphine-dependent rats, and the effect of naloxone, 0.5 mg/kg sc, and methylbromide naltrexone, 1.0 mg/kg sc, a peripheral opioid antagonist, on the MMC in morphine-naive and morphine-dependent rats. We also evaluated intestinal motility during naloxone-induced withdrawal in animals pretreated with clonidine, 100 micrograms/kg sc. Intestinal myoelectric activity was monitored by four indwelling electrodes in unanesthetized, fasted rats. D-[14C]xylose breath tests were performed before and after morphine-pellet implantation to evaluate the presence of bacterial overgrowth of the small intestine. Naloxone had no effect on myoelectric activity of the small intestine in morphine-naive rats. Cycling activity fronts were present in morphine-dependent animals, but there was a significant prolongation of activity front periodicity and slowing of the propagation velocity. No significant increase in 14CO2 excretion was noted in the morphine-dependent rats. After injection of naloxone, the morphine-dependent rats had a marked increase in spike activity with no identifiable activity fronts for 89 +/- 8 min. Similarly, methylbromide naltrexone disrupted activity fronts, but for a significantly shorter period. Clonidine prevented the marked increase in spike activity that occurred during naloxone-induced withdrawal. We conclude from our studies that myoelectric activity of the small intestine develops incomplete tolerance to morphine; bacterial overgrowth is not a feature of morphine dependence in the rat; alterations of intestinal myoelectric activity are a component of the opiate withdrawal syndrome, and they appear at least partially mediated by a peripheral mechanism that can be suppressed by an alpha 2-adrenergic agonist.
mesh_terms: D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004576:Electromyography; D007421:Intestine, Small / Q000382:microbiology / Q000503:physiopathology*; D009021:Morphine Dependence / Q000503:physiopathology*; D009130:Muscle, Smooth / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D010507:Periodicity; D051381:Rats; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D014994:Xylose / Q000378:metabolism
chemical_list: D009270:Naloxone; D014994:Xylose; D003000:Clonidine