OXYMORPHONE-INDUCED ANALGESIA AND COLONIC MOTILITY MEASURED IN COLORECTAL DISTENSION

Changes in colonic motility in rats following intravenous (IV) oxymorp hone, (0.1 mg/kg), atropine (0.1 mg/kg), or saline were monitored to d etermine whether opioid-induced changes in colonic motility affect ant inociceptive measurements when using colorectal distension (CRD) as a nociceptive assay. Polygraph recordings of colonic pressures, contract ion frequencies, and the pressure-volume relationship of the stimulus showed that oxymorphone produced a transient increase in contraction f requencies when compared to atropine- and saline-treated rats. The tra nsient increase in contraction frequency caused by oxymorphone decline d to baseline levels at 30 min after administration, the time at which the nociceptive threshold for CRD was tested. Neither oxymorphone nor atropine changed baseline pressures or the pressure-volume curve for the balloon stimulus. Antinociceptive results from CRD at 30 min postt reatment showed that only oxymorphone produced significant antinocicep tion. We conclude that oxymorphone does not produce changes in colonic motility that complicate antinociceptive measurements in CRD and that CRD is an effective means of testing opioid-induced visceral antinoci ception.