Steroidogenesis in fetal bovine gonads.

Gonadal steroidogenesis in bovine fetuses of 40 to 125 days gestation was examined using histochemical procedures and radioimmunoassay on gonadal cultures to determine the physiological correlates of gonadal morphogenesis in cattle. Gonadal morphology and the in vitro secretion patterns were distinct between the sexes by 45 days when testes secreted significantly higher levels of testosterone and androstenedione and lower levels of estrone and 17 beta-estradiol that the ovaries (p less than 0.0001). It would appear that the main steroid route in the ovaries of 45 to 70 day old fetuses is the androstenedione to estrone to 17 beta-estradiol pathway. The high estrone secretion and the decreasing levels of 17 beta-estradiol and testosterone in the ovaries of 70 to 125 day fetuses suggest an inhibition of 17 beta-hydroxysteroid dehydrogenase activity. It is postulated that this shift in steroid biosynthetic pathways may be related to the change in cellular events from mitosis to meiosis in fetal ovaries.