EXPRESSION AND IMMUNOLOCALIZATION OF FUNCTIONAL CYTOCHROME-P450 AROMATASE IN MATURE RAT TESTICULAR CELLS

Aromatase activity has been measured in Leydig cells and Sertoli cells from both immature and mature rats. Cytochrome P450 aromatase (P450(a rom)) has been immunolocalized in germ cells of the rodent, bear, and rooster. Our purpose was to investigate expression of and to immunoloc alize P450(arom) in adult rat testicular cells. After Western blotting with a specific anti-cytochrome P450(arom) antibody, we demonstrated the presence of a 55-kDa protein in mature rat seminiferous tubules an d crude germ cell preparations. Immunoreactive aromatase was detected both in cultured rat Leydig cells and in testis sections (interstitial tissue and elongated spermatids showed positive immunoreactivity for P450(arom)). We next used reverse transcription-polymerase chain react ion to localize and quantify the P450(arom) mRNA in the various testic ular cells. In rat Leydig cells, the amount of P450(arom) mRNA was 15 times higher than in Sertoli cells (34.1 +/- 3.2 to 2.3 +/- 0.2 x 10(- 3) amol/10(6) cells, respectively). In pachytene spermatocytes, round spermatids, and testicular spermatozoa the P450(arom) mRNA levels were 38.7 +/- 8.1, 20.4 +/- 3.8, and < 1.3 x 10(-3) amol/10(6) cells, resp ectively. The aromatase activity was 2.5-4 times higher in testicular spermatozoa (8.48 +/- 1.98 fmol/10(6) cells per hour) than in other ge rm cells. These results indicate that in mature rats, not only Leydig cells and Sertoli cells but also germ cells have the capacity to expre ss functional P450(arom). According to the germ cell maturation state, there was an inverse relationship between P450(arom) mRNA content and the biological activity of the protein. The expression of the functio nal P450(arom) in mature rat germ cells confirms the existence of an a dditional source of estrogens within the genital tract of the male.