Antagonistic effect of MR2266 and MR2267 on morphine or nalbuphine analgesia at the spinal levels in rats.

: The aim of this paper was to study the effect of two benzomorphan derivatives MR2266 and MR2267 with predominant antagonism to kappa-opioid receptors administered intrathecally on the analgesic action of morphine and nalbuphine. Both compounds attenuated the analgesia elicited by examined opioid agonists. Our results support the hypothesis that the spinal opioid receptors take part in analgesic effect of morphine and nalbuphine. It was for the first time described that MR2267, considered as inactive enantiomer of MR2266, is an active opioid antagonist when administered intrathecally.