Estradiol modulation of basal and gonadotropin-releasing hormone-induced gonadotropin release in intact and castrated men.

Abstract

In 6 intact and 4 castrated adult men a daily intramuscular administration of 1.5 mg estradiol benzoate (E2B) (at 08.00 h) for 7 days induced an initial suppression of circulating gonadotropins with a subsequent rise in LH, which occurred after 96 h of treatment in intact men and after 120 h in castrated men. The magnitude of the LH surge was greater in castrated than in intact men. The changes in basal LH levels were concomitant with a variation in the LH responses to GnRH infusion (0.2 µg/min × 4 h) suggesting a modulatory effect of estrogen on the two pools of pituitary LH. A dramatic decrease in the LH response during the first hour (first pool) was observed after 24-48 h of treatment, followed by a significant increment of this response, which occurred at 96 h in intact men and at 120 h in castrated subjects. During E2B administration, a progressive increment in the delayed response of LH (second pool) was seen, indicating an augmentation of the pituitary capacity. The basal FSH levels progressively decreased and the pattern of FSH response to gonadotropin-releasing hormone (GnRH) infusion was not significantly changed during E2B treatment. The present results demonstrated that:(1) the maintenance for 96-120 h of serum E2 concentrations similar to those present in women at midcycle induced a LH release both in intact and castrated men. (2) The magnitude of LH peak is blunted in the presence of circulating testosterone. (3) E2 induced a biphasic effect on the two pools of pituitary LH similar to that observed in women. Finally, our present data confirm our previous findings that the modulation of gonadotropin secretion in men is not influenced by the perinatal exposure of the hypothalamic-pituitary unit to androgens.