The effect of estrogens on luteinizing hormone plasma levels and on testosterone production in intact and hypophysectomized rats.

Abstract

Intact male rats were injected with 50 μg E2B (estradiol benzoate) or with 100 μg E2 (estradiol). Six hours after injection plasma and testicular testosterone levels and production were significantly decreased. Concomitant with this change lowered LH plasma levels could be observed in the estrogentreated animals. Twenty-four hours after injection of 50 μg E2B LH levels, testosterone levels and testicular testosterone production were still reduced, whereas 24 h after E2 administration both testosterone and LH levels had returned to control levels. One and 3 h after injection of 500 ng estradiol, plasma and tissue testosterone levels, as well as testicular testosterone production, were decreased. However, this low dose of E2 also caused a decrease in LH plasma levels. In order to investigate whether estrogens would inhibit testicular testosterone synthesis or release by mechanisms other than inhibition of LH secretion, estrogen or vehicle only were injected into hypophysectomized animals given exogenous LH. No effects of estrogens on testosterone levels or production were observed in such animals. These findings suppport the view that the observed effect of administered estrogens on testosterone production in rat testicular tissue reflect primarily extra-testicular estrogen actions such as the negative feedback effect on LH secretion.