[Failure of positive feedback in hypothalamo-pituitary-system in aged women and its recovery with estrogen treatment].

The positive feedback function of the hypothalamo-pituitary system in aging women was investigated by means of intravenous injection of conjugated estrogens. Marked LH surge was observed in both sexually mature young (20-35 y.o.) and premenopausal (35-49 y.o.) women after the intravenous injection of 20mg of conjugated estrogens. However, merely a small LH surge was observed in postmenopausal climacteric (50-55 y.o.) women, and no LH surge in aged (over 56 y.o.) women. In the patients with hypergonadotropic hypogonadism who are in the same age as sexually mature women, no LH surge was induced by conjugated estrogens. But positive feedback test done after oral administration of conjugated estrogens (1.25 mg/day) for 14 days showed positive reaction in both the aged women and the patients with hypergonadotropic hypogonadism in whom no LH surge had been observed before estrogen priming. The present results suggest that the dysfunction of positive feedback in aged women is mainly due to the decreased levels of estrogen produced by the ovaries but not the primary organic or functional changes of the hypothalamus or the pituitary.