hCG-induced inhibition of testicular steroidogenesis: an oestradiol-mediated process?

Single i.v. injections of hCG (10 U) in adult male rats resulted, within 24 h, in a 2-fold decrease in the maximal LH-stimulated testosterone production in vitro, while pregnenolone production was not changed. In addition to the changes in steroidogenesis, a concomitant depletion of the oestradiol-cytosol receptor was observed. In contrast with the observations after 24 h, a 2-fold increase in both testosterone and pregnenolone production was observed at 72 h after a single i.v. injection of hCG (10 U). At 72 h after the hCG treatment, oestradiol-cytosol receptor levels were not different from values observed after injection of saline. Tamoxifen administration (50-500 microgram s.c. injections) resulted, within 24 h, in depletion of oestradiol-cytosol receptor levels. This decrease of oestradiol binding, however, was not paralleled by decreases in testosterone production. Simultaneous administration of tamoxifen and hCG did not prevent the hCG-induced inhibition of testosterone production observed 24 h after administration of hCG. It is concluded that the present results offer no proof for an obligatory role of the oestradiol receptor in gonadotropin-induced inhibition of testosterone production in testicular Leydig cells.