Steroid and FSH action on LH receptors and LH-sensitive testicular responsiveness during sexual maturation of the rat.

This study examines the effect of FSH, testosterone and estradiol on testicular LH receptors and in vitro testicular responsiveness to LH in immature rats under various conditions. FSH treatment of 15-day-old immature rats significantly increased the number of LH receptors but did not alter testicular responsiveness. FSH treatment of hypophysectomized immature rats increased the number of LH receptors and markedly increased testicular responsiveness. Treatment of hypophysectomized rats with testosterone proprionate for 4 days, followed by a 5-day treatment with FSH, enhanced the effect of FSH on the number of LH receptors but did not increase the effect of FSH on testicular responsiveness. In contrast, treatment with estradiol for 4 days before FSH treatment had no effect on the FSH-induced increase in LH receptors but completely inhibited the FSH-induced increase in testicular responsiveness. These observations suggest that during male sexual maturation (1) regulation of LH receptors is distinct from regulation of testicular responsiveness to LH, (2) estradiol may be a factor in the regulation of testicular responsiveness to LH, and (3) testosterone may enhance the FSH-induced increase of LH receptors.