Abstract
Proestrus surges of serum LH, FSH and prolactin (PRL) were significantly reduced when morphine HCl (50 and 10mg/kg) was administered to 4-day cycling rats just prior to the proestrous critical period. The inhibitory effect ofmorphine was reversed by naloxone, a morphine antagonist, at the dose which had no effect on the proestrus surges of serum LH, FSH or PRL. The hypothalmic LH-RF content of proestrous rats at 1800 hr (during the proestrus surge) was not significantly different from that at 1400 hr (before the surge) and was not affected by pretreatment with morphine or naloxone. Our results suggest that naloxone reverses the antiovulatory effect of morphine by antagonizing the inhibitory effect of morphine on preovulatory surges of gonadotropins or PRL.
