Background: Progesterone is a female steroid hormone that has a potent anticonvulsant effect on human and animal. The aim of this study was to investigate the involvement of opioid receptors in the anticonvulsant effect of progesterone on ovariectomized mice.

Materials and Methods: In this experimental study, all animals were ovariectomized. After two weeks, they received an intraperitoneal (i.p.) injection of drugs (progesterone and naloxone) or saline. The animals also received a subcutaneous injection of strychnine for induction of convulsive seizures, 30 minutes after administration of drugs or saline. For evaluation of convulsion in the animals, convulsion onset time, convulsion duration, the number of seizures, and death time were recorded.

Results: Progesterone (25 and 50 mg/kg, i.p.) decreased the strychnine-induced convulsion. The anticonvulsant effect of 50 mg/kg of progesterone was abolished by naloxone (5 mg/kg, i.p.) injection, whereas administration of the same doses of naloxone alone did not affect strychnine-induced convulsion.

Conclusion: These results suggest that opioid receptors may play an important role in the anticonvulsant effect of progesterone.