Evidence for a Leydig cell progesterone receptor in the rat.

Tritiated promegestone [3H] R 5020 is bound with high affinity by charcoal-treated cytosol prepared from purified Leydig cells. The binding is characterized by high affinity (Kd = 2 x 10(-9) M) and specificity (R 5020 = progesterone greater than testosterone = dehydrotestosterone greater than hydroxyprogesterone greater than cortisol = dexamethasone greater than estradiol) appropriate for progesterone receptors. In vitro, progestin-bound cytosol was quantitatively translocated to nuclei fractions, only if cytosol samples were previously labeled at 25 degrees C. However no translocation of binding activity was observed when previous cytosol labeling was done in the presence of sodium molybdate. Effects of glucocorticoids, androgens and estrogens on the Leydig cell are well documented, the demonstration of a putative progesterone receptor raises the possibility of direct effect of progesterone on the Leydig cell.