The disappearance of opioidergic regulation of gonadotropin secretion in postmenopausal women.

In postmenopausal women, the administration of beta-endorphin in repeated pulses (1-2.5 mg) at 1- to 2-h intervals or constant infusion (1 mg/h) for 3-6 h elicited the prompt release of PRL without concomitant change in LH levels. Infusion of an opiate receptor antagonist, naloxone (1.6 mg/h), for 6-7 h also had no effect on LH levels. Since substantial evidence indicates that endogneous opioid peptides exert an inhibitory role on GnRH-LH secretion and that the functional activity of opiate receptors appears to be ovarian steroid dependent, the present observation suggests that the hypersecretion of gonadotropin in the absence of ovarian steroid feedback may, in part, be causally related to a reduced opioid inhibition of GnRH-LH release.