Does the gonadotropin pulsatility of postmenopausal women represent the unrestrained hypothalamic-pituitary activity?

Ovarian sex steroids profoundly modulate the gonadotropin pulsatile secretion in women. A gonadotropin pulsatility determined in the absence of any considerable ovarian sex steroid feedback, as in postmenopausal women (PMW), may thus represent the unrestrained activity of the hypothalamic-pituitary axis. We hypothesized that increases in the gonadotropin pulse frequencies and amplitudes during sex steroid replacements may be limited by those determined in the hypogonadal state of PMW. To address this assumption, we investigated the unstimulated the gonadotropin-releasing hormone (GnRH)-stimulated release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in PMW before and during sequential ovarian sex steroid treatments. Seven PMW (mean age 59.4 years) were studied initially during unreplaced conditions (control studies), then on the last day of a 21-day course of oral estradiol valeriate (E2) administrations (2 mg daily) and, finally, on the last day of a 21-day course of oral estradiol-progesterone (E2/P4) replacements (2 mg of E2 and 200 mg of micronized P4 daily). On all study occasions, blood was drawn at 10-min intervals for 10 h and GnRH (25 micrograms iv) was administered 8 h after initiation of blood collections. Compared to control conditions, the basal serum estrogen (estrone and E2) and progesterone (P4) concentrations markedly increased (p < 0.001) following oral E2 or E2/P4 treatments. As determined by Cluster pulse algorithm, LH and FSH were found to be released episodically during each study condition. Mean LH and FSH release rates declined (P < 0.05 or less) during E2 and E2/P4 regimens.(ABSTRACT TRUNCATED AT 250 WORDS)