Neuroendocrinology of aging in humans: attenuated sensitivity to sex steroid feedback in elderly postmenopausal women.

Studies in experimental animals have shown that the sensitivity of the hypothalamic-pituitary system to ovarian sex steroid feedback declines while aging progresses. Since similar observations are lacking in humans, we studied the gonadotropin secretion of postmenopausal women (PMW) of different ages before and following a 7-day course of oral clomiphene citrate (CC, 100 mg daily). For serial determinations of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels, blood was sampled frequently from 5 younger PMW (mean age 55.2 years) and 6 older PMW (mean age 80.3 years) for 10 h. Eight hours after initiation of blood sampling, gonadotropin-releasing hormone (GnRH, 25 micrograms) was administered. Compared to untreated conditions, CC administration did not significantly change the serum concentrations of the estrogens (estrone, estradiol) and androgens (testosterone; androstenedione, dehydroepiandrosterone sulfate). However, CC increased the sex hormone-binding globulin levels in both younger and older PMW, suggestive of the estrogenic effects of this compound. In the unstimulated secretory profiles of younger PMW, mean LH levels decreased (p < 0.05) in response to CC, presumably a consequence of decreased (p < 0.05) pulse frequencies, but not pulse amplitudes. Likewise, by virtue of decreased (p < 0.05) FSH pulse amplitudes, FSH levels declined (p < 0.05) in younger PMW. In contrast, both the LH and FSH levels and their pulsatility remained virtually unaltered following CC administrations to older PMW. The GnRH-mediated gonadotropin release was uneffected by CC administrations in either group of PMW.(ABSTRACT TRUNCATED AT 250 WORDS)