Translocation of the testicular estradiol receptor is not an obligatory step in the gonadotropin-induced inhibition of C17-20-lyase.

We have investigated the effects of hCG and estradiol on the time course of the inhibition of C17-20-lyase and the depletion of the estradiol cytosol receptor in testicular tissue of male rats. In hCG-treated animals the first significant decrease in C17-20-lyase activity was observed 16 h after injection of the hormone. The C17-20-lyase activity decreased further during the following 56 hours. Estradiol-cytosol receptor levels were significantly decreased 7 hours after the hCG injection, and after a nadir at 16 hours increased to 130% of control values at 72 hours. In contrast, in the estradiol-treated animals the first significant inhibition of C17-20-lyase activity could be observed only after 24 h, while a 95% depletion of estradiol-cytosol receptor levels was observed already within 1 h after administration of the hormone. These results demonstrate that a rapid estradiol-induced depletion of the estradiol receptor as such does not necessarily result in a subsequent immediate inhibition of the C17-20-lyase. The rapid inhibition of this enzyme after hCG indicates, therefore, that other mechanisms are involved.