Morphine inhibition of ovulation: reversal by naloxone

The effect of naloxone (N-allylnoroxymorphone), a narcotic antagonist, on the morphine blockade of ovulation was studied. Female rats were treated with morphine (50 mg/kg) at the critical period, resulting in ovulatory blockade. The administration of naloxone (0.5 mg/kg) effectively reversed the anti-ovulatory effect of morphine. The antagonist reversed the morphine effect when given 1 hour before (75% reversla), simultaneously (75% reversal), and up to 3 hours after morphine treatment (63% reversal). The number of ova shed per animal was not affected by naloxone treatment with or without morphine. When the blockade of ovulation occurred in animals treated with both naloxone and morphine, uterine distension was present in 85% of the animals on the day of estrus.