Effects of Gonadotropins on Steroid Secretion by Infantile and Juvenile Mouse Ovaries in Vitro*

The steroidogenic potential of ovaries from infantile and juvenile mice was analyzed’ using organ culture with defined medium. In initial experiments, pieces of ovaries from 2-, 7-, 11-, 15-, and 20-day-old B6D2F1 mice were cultured in medium without added hormones or with 2 μg biological grade FSH (NIAMDD-rat FSH-B-l)/ml for 48 h, and the media were subsequently analyzed by RIA for progesterone, testosterone, 17β-estradiol, and androstenedione. Ovaries from 2-day-old mice did not secrete detectable quantities of these steroids, and secretion was not stimulated by FSH. In the other four age groups, biological grade FSH greatly increased the secretion of all four steroids compared with the controls. The remaining experiments focused on the 7-day-old mice. To determine whether FSH or contaminating LH in the biological grade FSH stimulated steroid secretion, pieces of 7-day-old ovaries were cultured in medium without added hormones or with 100 ng/ml of the following purified gonadotropins: LH (NIAMDD-rat LH-I-4), FSH (NIAMDD-rat FSH-I-3), and LH plus FSH. Although purified FSH slightly stimulated testosterone and progesterone secretion, purified LH stimulated testosterone and progesterone secretion to the same extent as the biological grade FSH and the combination of LH plus FSH. Both purified LH and FSH stimulated estradiol secretion (P < 0.005), but the combination of the two purified gonadotropins stimulated significantly more (P < 0.005) estradiol secretion than either alone. Ovaries incubated with FSH plus testosterone, but not with FSH plus DHT (a nonaromatizable androgen), secreted levels of estradiol comparable to those produced in the presence of FSH and LH. These results suggest that in 7-day-old mouse ovaries, LH promotes estradiol production by stimulating the synthesis of androgen precursor, which is subsequently aromatized in response to FSH. Light and electron microscopic examination of fresh and cultured ovaries from 7-day-old mice showed that follicles contained one or two layers of granulosa cells surrounded by a clearly defined theca. No differentiated interstitial tissue was observed. These results indicate that in immature mouse ovaries 7 days of age or older, steroid production in vitro can be stimulated with gonadotropins and suggest that as early as 7 days of age, LH and FSH interact to promote estradiol production.