Effect of Ovine FSH and LH on Serum Steroids and Ovulation in Hypophysectomized Immature Female Rats1

Experiments were designed to determine the effect of highly purified ovine FSH and LH on serum steroid levels and ovulation. Immature female rats were hypophysectomized at 28 days of age. Beginning 7 days after hypophysectomy the rats were injected subcutaneously twice daily over a period of 4 days with either 1.0 µg ovine FSH in 0.5 ml saline or 0.5 ml saline per injection (priming dose). On the morning of day 39, 8 µg FSH or 1.28 fig LH (ovulating dose) were administered intravenously via the tail vein. The maximum number of LH units administered in the FSH ovulatory dose (equivalent to 0.0004 U NIH LHSl) was well below the minimal effective dose of the LH preparation (0.005 U NIH LH-S1) required for ovulation. Serum levels of progesterone, 20±-dihydroprogesterone, estrone and estradiol were determined by radioimmunoassay after 1 and 4 days of priming and after ovulation. Serum levels of progesterone were maintained during the 4 days of FSH priming. After a single day of FSH priming 20a-dihydroprogesterone levels (6.1 ng/ml) were significantly higher than saline controls (1.7 ng/ml). However, by the fourth day of FSH priming, the 20±-dihydroprogesterone levels had decreased significantly (1.1 ng/ml). Four days of FSH priming caused significant increases in estrone (from 23.1 to 48.5 pg/ml) and estradiol (from 2.2 to 66.7 pg/ml). The number of ova found in FSH-ovulated animals (32) was not significantly different from the number found in LHovulated animals (46). A 50-fold increase in 20± dihydroprogesterone was observed after FSHinduced ovulation (57.6 ng/ml) and a 10-fold increase after LH-induced ovulation (12.6 ng/ml). The levels of 20±-dihydroprogesterone in FSH-ovulated animals were significantly higher than levels in LH-ovulated animals. Progesterone also increased, from 2.5 ng/ml prior to ovulation to 6.6 and 8.3 ng/ml in FSH- and LH-ovulated animals, respectively. There were no differences in serum estrone levels in animals ovulated with LH (23.2 pg/ml) and FSH (28.8 pg/ml). However, the levels of estradiol in animals ovulated with FSH (36.6 pg/ml) were significantly higher than levels in LH-ovulated animals (4.6 pg/ml). These results indicate that in addition to its well-established role in follicular development and maturation, FSH is also capable of altering serum steroid levels and of inducing ovulation in hypophysectomized immature female rats.(Endocrinology95: 682, 1974)