Augmentation of aromatase activity by FSH in ovaries of fetal and neonatal mice in organ culture.

The stimulative effect of FSH on aromatase activity was investigated in ovaries of fetal (on days 17 and 18 of gestation) and neonatal mice (on days 0, 3, 6 and 9 after birth). Two to six ovaries, were cultured for 48 h in 2 ml of Medium 199 supplemented with insulin (5 micrograms/ml) and [1 alpha, 2 alpha, 6 alpha, 7 alpha, beta-3H]4-androstene-3,17-dione (0.35 microM) in the presence or absence of porcine FSH (0.5 units/ml) and the amount of [3H]oestradiol-17 beta and [3H]oestrone produced was estimated. In the presence of FSH, aromatase activity per ovary, which was found in all fetal and neonatal ovaries examined, increased with age. In the absence of FSH, however, the production of oestrogens could be demonstrated only in ovaries from 3- to 9-day old mice. FSH increased the aromatase activity by up to 10-fold. In spite of the stimulative effect of FSH on aromatase activity, FSH exerted no significant effect on DNA synthesis of the ovaries. The formation of primordial follicles could not be observed histologically in ovaries of fetal mice on day 17 of gestation, although the ovaries of 6- and 9-day old mice contained multilayered follicles. These results show that FSH stimulates the aromatase activity of the mouse ovary even before the formation of primordial follicles and that the stimulative effect of FSH on ovarian aromatase is not due to the proliferation of ovarian cells.