ANDROGEN RECEPTOR GENE-EXPRESSION IN RAT GRANULOSA-CELLS - THE ROLE OF FOLLICLE-STIMULATING-HORMONE AND STEROID-HORMONES

In rat ovary, androgen receptor (AR) is predominantly expressed in gra nulosa cells and is developmentally regulated. However, the exact mech anism that is responsible fur the regulation of AR in granulosa cells has not been elucidated. The aim of this study was to examine 1) the l evels of AR messenger RNA (mRNA) expression in granulosa cells from fo llicles of different size and 2) the effects of FSH, 8-bromo-cAMP, and rogen, and estrogen on AR mRNA levels in granulosa cells in vitro. The abundance of AR mRNA was examined by ribonuclease protection assay us ing P-32-labeled AR complementary RNA probe and related to that of P45 0aromatase (P450arom) mRNA, a well established maker of granulosa cell differentiation. In large follicles (>400 mu m in diameter), the abun dance of AR mRNA was decreased to 51% of that in small follicles (<200 mu m; P < 0.01), whereas the abundance of P450arom mRNA increased to 277% (P < 0.01). In medium follicles (200-400 mu m), the abundance of AR mRNA was maintained (101%), whereas the abundance of P450arom mRNA increased to 202% of that in small follicles (P < 0.05). Treatment wit h FSH (0-300 mu g/ml) or 8-bromo-cAMP (0-4 mM) induced P450arom mRNA i n the cultured granulosa cells in a dose-dependent manner; however, it did not affect tile levels of AR mRNA expression. Treatment with 5 al pha-dihydrotestosterone (1 mu) resulted in a significant reduction in the abundance of AR mRNA to 67% of the control value (P < 0.05). This effect was reversed by the addition of FSH (100 ng/ml; P < 0.01). Trea tment with diethylstilbestrol (1 mu M), alone or in combination with F SH (100 ng/ml), did not have any significant effect; although these tr eatments tended to decrease the abundance of AR mRNA to 81% and 85%, r espectively. Both 5 alpha-dihydrotestosterone and diethylstilbestrol d ramatically enhanced the abundance of FSH-induced P450arom mRNA compar ed to the effect of FSH alone. These results indicate that 1) the down -regulation of AR mRNA expression takes place in granulosa cells of pr eovulatory follicles; 2) FSH is not directly responsible for this even t. and 3) androgen down-regulates AR mRNA expression in immature granu losa cells, and this effect is reversed by FSH. We conclude that andro gen and FSH jointly regulate AR mRNA expression in rat granulosa cells .