Abstract
Summary
In ovariectomized rats given estradiol benzoate (EB), followed 3 days later by EB or progesterone, morphine, and naloxone altered the LH and FSH surges on the day of treatment (Day 1) and on the next day (Day 2). In the EB-EB-treated rats, morphine prevented, whereas naloxone enhanced the surge of LH and FSH on Day 1. On Day 2, the morphine-treated rats showed a large rebound surge of LH and FSH, whereas the naloxone-treated rats showed no surge. In the EB-progesterone-treated rats, morphine blocked, whereas naloxone had no effect on the LH and FSH surge on Day 1. On Day 2, the morphine-treated rats showed a large LH and FSH surge, whereas the naloxonetreated rats showed no surge. The effects of these drugs on the Day 2 surge of LH and FSH were found not to be the result of a build up or depletion of releasable stores of LH in the pituitary on Day 1. These results suggest a possible role for the endogenous opioid peptides in modulating steroid regulation of the neural surge signal for LH and FSH.
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