Antinociceptive effect of dihydroetorphine in diabetic mice.

The antinociceptive potency of dihydroetorphine in diabetic mice was examined. Subcutaneous administration of dihydroetorphine produced a dose-dependent antinociception in both non-diabetic and diabetic mice. The antinociceptive potency of s.c. dihydroetorphine was less in diabetic mice than in non-diabetic mice. The antinociception induced by i.c.v. dihydroetorphine (0.02 microgram) was also significantly less in diabetic mice than in non-diabetic mice. The antinociceptive effects of dihydroetorphine (10 micrograms/kg i.p.) in both diabetic and non-diabetic mice were significantly antagonized by s.c. administration of beta-funaltrexamine, a selective mu-opioid receptor antagonist. Furthermore, the antinociceptive effect of dihydroetorphine (10 micrograms/kg i.p.) in non-diabetic mice, but not in diabetic mice, was also significantly antagonized by naloxonazine, a selective mu 1-opioid receptor antagonist. The time course and the potency of the antinociceptive effect of dihydroetorphine (10 micrograms/kg i.p.) in diabetic mice were similar to those in naloxonazine-treated non-diabetic mice. Naltrindole, a selective delta-opioid receptor antagonist, or nor-binaltorphimine, a selective kappa-opioid receptor antagonist, had no significant effect on the antinociceptive effect of dihydroetorphine (10 micrograms/kg i.p.) in both diabetic and non-diabetic mice. These results suggest that dihydroetorphine produces an antinociceptive effect through the activation of both mu 1- and mu 2-opioid receptors in mice. Furthermore, the reduction in dihydroetorphine-induced antinociception in diabetic mice, as compared with non-diabetic mice, may be due to the hyporesponsive to supraspinal mu 1-opioid receptor-mediated antinociception in diabetic mice.