Androstenedione metabolism in the indifferent stage of bovine gonad development

Suspensions of cells obtained from genital ridges and gonads of bovine embryos of 1.0-3.4 cm in crown-rump (C-R) length were used for studies of the metabolism of radiolabeled exogenous steroid precursor. Tritiated androstenedione was employed as precursor and the final products of their metabolism were evaluated after separation by thin-layer chromatography. Genetic sex was determined by the karyotype of hepatocytes from the same embryos. The extent of conversion of tritiated androstenedione was higher in cells from male embryos than cells from female embryos. Furthermore, androstenedione was metabolized mainly to testosterone in male embryos. By contrast, cells obtained from female embryos transformed androstenedione to estrone and 17 beta-estradiol. The onset of this activity was observed at 1.8 cm in C-R length in males and at 2.2 cm in C-R length in females. In all cases, after the onset, the metabolic activity increased in relation to the age of the embryos. These data show that in the bovine embryo gonad, the activity of aromatase and 17 beta-hydroxysteroid dehydrogenase are present when the morphological differentiation of the gonadal sex has not yet been established.