Effect of follicle-stimulating hormone (FSH) and estrogen on follicle growth in rats

Effects of hysterectomy on ovulation and related ovarian functions in regular estrous cycle rats

The number of ovulation was significantly higher in hysterectomized rats with regular estrous cycles than in sham-operated rats at the estrous stage 20-24 days after operations (13.2 +/- 0.33 vs. 11.8 +/- 0.41, P < 0.05). This finding suggests that hysterectomy facilitates the follicular maturation in rats. To examine the mechanism of facilitation on follicular maturation in hysterectomized rats, plasma FSH level, ovarian estradiol-17 beta (E2) and ovarian aromatase activity were measured 20 days after hysterectomy. Hysterectomy had no effect on plasma FSH levels at any of the estrous stages. Ovarian E2 level and aromatase activity (AA) were significantly increased by hysterectomy only at diestrus-2 stage of the estrous cycle (E2; 3.76 +/- 0.49 vs. 1.48 +/- 0.49 ng/g ovarian tissue, P < 0.05, AA; 1.36 +/- 0.15 vs. 0.83 +/- 0.11 pmol/h. mg ovarian tissue, P < 0.05), but ovarian testosterone level was not affected by the operation. These results support the hypothesis that in rats hysterectomy facilitates follicular maturation. This may be due to an increase in ovarian E2 level at the diestrus-2 stage, caused by heightened ovarian aromatase activity.

Inhibitory effect of progesterone on follicular growth and induced superovulation in the rat

We investigated the effect of exogenous progesterone on follicular growth and pregnant mares' serum gonadotropin and human chorionic gonadotropin (PMS-HCG) induced superovulation in intact and hypophysectomized immature rats. Although the administration of progesterone during PMS-HCG injections had no effect on superovulation, the administration of progesterone beginning 3 days before PMS injection inhibited superovulation in both intact and hypophysectomized rats. In order to study the mechanism of inhibition of superovulation by pretreatment with progesterone, an autoradiographic study using tritiated thymidine was done in hypophysectomized rats just before PMS injection. The labelling indices of granulosa cells were significantly decreased by the administration of progesterone (p < 0.001). Treatment with progesterone resulted in an increase of the follicles in early stages of atresia with pycnotic nuclei in granulosa cells surrounding apparently normal oocytes. Ovarian histology and serum and ovarian tissue concentrations of estradiol were then examined in hypophysectomized rats 20 h after HCG injection. Large Graafian follicles and corpora lutea were rarely seen in rats previously given progesterone, whereas many large Graafian follicles and corpora lutea were observed in the control rats. The concentrations of estradiol in the progesterone-pretreated rats were significantly reduced in serum (p < 0.02) and slightly reduced in ovarian tissues when compared with controls.