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.