Effects of acute ovariectomy on the lordosis response of female rats.

The sexual receptivity of intact females with 4- or 5-day estrous cycles was compared to that of other females which had been ovariectomized at particular times during their cycles. The quality and frequency of lordosis responding were more degraded the earlier during the cycle ovariectomy was performed. This effect was more pronounced in 4-day than in 5-day cyclic females. Because exogenous progesterone was administered to all ovariectomized females, these behavioral deficits were attributed to removal of ovarian estradiol. Ovariectomy 6 hr before the critical period for luteinizing hormone release significantly shortened the duration of behavioral estrus, even though it had no effect when lordosis was tested at the time intact estrous females are maximally receptive. These findings are consistent with the hypothesis that the continual availability of estradiol throughout the 18--24 hr interval perior to the onset of behavioral estrus is essential for optimal conditioning of sexual receptivity to occur under physiological conditions. The relevance of triggering and maintenance functions of estradiol to these results is discussed.