Regulation of cytochrome P450 aromatase gene expression in adult rat Leydig cells: comparison with estradiol production

Regulation of aromatase gene expression in purified rat Leydig cells has no t yet been investigated. Therefore, using a highly specific quantitative RT -PCR method, we have measured the amount of cytochrome P450 aromatase (P450 arom) mRNA and aromatase activity in mature rat Leydig cells submitted to v arious treatments during 24 h. Estradiol production was enhanced in a dose- related manner in the presence of testosterone, the maximum (28% increase) being obtained with 200 ng/ml. Related to the P450arom mRNA levels, a decre ase was observed in the presence of low concentrations (50 and 100 ng/ml) o f testosterone, then a 20% increase of the amount of transcripts was record ed for the higher concentrations (200-500 ng/ml). The same result was obtai ned in the presence of 5 alpha -dihydrotestosterone (an androgen resistant to aromatase activity). The addition of ovine LH (oLH; 0.1-50 ng/ml) to the Leydig cell culture medium induced a dose-related augmentation of estradio l output up to 10 ng/ml oLH, although a decrease was observed with 50 ng/ml when compared with maximal values. mRNA levels slightly decreased in the p resence of low concentrations (0.1-1 ng/ml) of oLH, an effect that was abol ished by the addition of testosterone; mRNA levels were increased by oLH (5 -10 ng/ml) 35 and 75% respectively in the absence and presence of testoster one (when compared with Leydig cells incubated without treatment). With 50 ng/ml oLH, a large augmentation (twofold) of the P450arom mRNA level either without or with testosterone was observed. Dibutyryl cyclic AMP (1 mM) mim icked the effect of oLH. The half-life of the P450arom mRNAs was twofold in creased in the presence of testosterone and oLH when compared with the half -life in the absence of treatment (5.8 +/- 0.6 h). Taken together, our data have demonstrated that, in freshly isolated Leydig cells from mature rat t estes, the regulation of aromatase expression and enzymatic activity is und er LH (through cyclic AMP) and steroid control; moreover seminiferous tubul e-secreted factor(s) are also involved. Therefore, rat Leydig cell aromatas e is controlled at both transcriptional and post-transcriptional steps by e ndocrine and/or locally produced modulators.