[Male germ cells. A new source of estrogens in the mammalian testis].

Cytochrome P450 aromatase (P450arom), which catalyzes irreversible transformation of androgens into estrogens, has been immunolocalized in mouse, brown bear and rooster germ cells. In the immature rat, P450arom is found in Sertoli cells while in the mature rat it is found in Leydig cells. In the pig, ram, and human, it is mainly present in Leydig cells. Our purpose was first to investigate the testicular presence of cytochrome P450arom mRNA in adult rat germ cells using RT-PCR. The amplified product from germ cells showed 100% homology with the corresponding fragments of the rat ovary cDNAs and was detectable not only in rat Leydig and Sertoli cells but also in pachytene spermatocytes, round spermatids and testicular spermatozoa. In purified Leydig cells and pachytene spermatocytes the P450arom mRNA level was 10-fold higher than in Sertoli cells. The amount of P450arom mRNA transcript decreased according to the stage of germ cell maturation, being more elevated in younger than in mature germ cells. By contrast, the aromatase activity in the microsomal fractions was 2- to 4-fold greater in spermatozoa than in the other enriched germ cell preparations studied. We also demonstrated the presence of a 55kDa protein in a mixed germ cell preparation and have been able to immunolocalize the P450arom on mature rat testicular slices, namely in Leydig cells and elongated spermatids. The overall data confirm the presence of a functional cytochrome P450arom in the male rat testis and consequently, the existence of an additional source of estrogens within the genital tract of the male which may likely suggest a physiological role for these hormones in the regulation of spermatogenesis.