ACUTE DOPAMINERGIC BLOCKADE AUGMENTS THE NALOXONE-INDUCED LH RISE IN ESTROGEN-TREATED POSTMENOPAUSAL WOMEN

Objectives: To assess the effect of estrogen replacement on the simult aneous blockade of the dopaminergic (DA) and opioidergic neural contro l of hypothalamic-gonadotropic function in postmenopausal women. Metho ds: Twenty healthy postmenopausal women, 48-55 years old were randomly assigned to receive either a 4-h naloxone infusion at 2 mg/h (group 1 , n = 7) or a 10 mg i.v. bolus of metoclopramide (group 2, n = 7) or b oth drugs: simultaneously (group 3, n = 6) before and after 3 weeks of transdermal estradiol (100 mu g/day). Blood samples were obtained at 30-min intervals during 4 h and duplicate determinations of serum foll icle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E -2) and prolactin (PRL) were performed in all samples. Results: In gro up 1 only a mild but significant LH rise after but not before estrogen replacement was seen. In group 2 PRL had a greater rise after than be fore estrogen therapy, without other hormonal changes. In group 3 a gr eater rise in PRL occurred after than before estrogen administration a nd serum LH had a sustained rise throughout the test only after estrog en replacement (greater than in group 1). No FSH changes were observed . The after-estradiol PRL response was nearly similar in groups 2 and 3. Conclusions: Our results indicate that in the untreated postmenopau sal women, the dopaminergic system has little and the opioidergic syst em has no significant input in the control of gonadotropin or prolacti n release. However, following estrogen replacement, opioids are involv ed in the inhibition of LK release and stimulating PRL release, while the dopaminergic system acts to inhibit PRL release and modulates LH r elease or inhibition, depending on the levels of circulating estrogens . (C) 1997 Elsevier Science Ireland Ltd.