Opiatergic control of LH secretion is eliminated by gonadectomy

We have studied the stimulatory effects of naloxone and the inhibitory influence of the opiate peptide, FK 33-824, on LH secretion in the gonadectomized rat. Our results indicate that endogenous and exogenous opiate involvement in LH release disappear coincident with the removal of gonadal steroid feedback. At 7 days post-surgery naloxone is no longer able to stimulate LH secretion in male or female rats. Similarly, by 7 days in the male, and 21 days in the female, FK 33-824 is unable to inhibit LH secretion. We conclude that the coupling of hypothalamic opiate receptors to the LH regulatory mechanisms is dependent upon gonadal steroids. The most important of these appear to be estradiol and testosterone, since careful priming of long-term gonadectomized rats with these steroids is able to largely restore the LH responses to naloxone and FK 33-824.