[Transformation of 19-hydroxyandrostenedione to estrone and estradiol by rat embryonic testis in vitro].

Aromatase activity in the foetal rat testis was demonstrated by the conversion of [3H] testosterone into oestradiol. However, the conversion rate was low, around 0.06%, probably because the radioactive precursor was heavily diluted by the large amounts of endogenous testosterone produced. In an attempt to improve the conversion rate, we therefore used a precursor following testosterone on the oestrogen biosynthesis pathway. Testes from 18-21-day-old foetal rats were cultured in vitro with [3H] 19-hydroxyandrostenedione as a substrate in the presence or absence of LH, FSH or (Bu)2 cAMP. The [3H] oestrone and [3H] oestradiol synthesized were measured by double isotopic dilution and recrystallization to constant specific activity. In comparison with previous results obtained with testosterone as precursor, the synthesis rate of oestrogens was increased 5-10-fold. FSH and (Bu)2 cAMP stimulated aromatase activity; LH had no effect. These results definitively establish the capacity of the foetal rat testis to aromatize androgens.