Estrogens in the feedback regulation of gonadotropin secretion in men: effects of administration of estrogen to agonadal subjects and the antiestrogen tamoxifen and the aromatase inhibitor delta'-testolactone to eugonadal subjects.

To elucidate the specific role of estrogens in the feedback regulation of gonadotropin secretion in men, basal and LRH-stimulated gonadotropin levels were studied in: Six agonadal subjects Six agonadal subjects continuously treated with 50 micrograms ethinylestradiol Six eugonadal subjects, treated with the aromatase inhibitor delta'-testolactone, which induced a reduction of estrogen levels, independently of testosterone. Further, to determine whether estrogens exert differential effects in time on LH and FSH secretion, the anti-estrogen tamoxifen was administered to: Six eugonadal subjects for two weeks and Six eugonadal subjects for six weeks. It was found that estrogens have a strong suppressive effect on both LH and FSH secretion. However, changes in estrogen levels and blocking of estrogen receptors are followed more rapidly by FSH than LH. Estrogens affect LRH-induced LH release more than basal LH levels; basal and LRH-stimulated FSH are approximately equally influenced. Basal and LRH-induced LH secretion are known to be more dependent upon previous LRH stimulation than FSH secretion. Since FSH followed changes of estrogens more rapidly than LH did, we postulate that the negative feedback action of estrogens on: LH secretion is predominantly exerted at the level of the hypothalamus, through inhibition of LRH secretion FSH secretion predominantly at the level of the pituitary through a direct action on the gonadotroph.