Estradiol induced luteal regression in unilaterally hysterectomized and luteinizing hormone-treated ewes.

Abstract

The effect of exogenous estradiol on luteal weights in unilaterally hysterectomized ewes was studied in two experiments. Ewes were unilaterally hysterectomized on day 5 of the estrous cycle (first day of estrus=day zero of the cycle). Estradiol (1 mg) was injected intramuscularly on each of days 11 and 12 of the estrous cycle. All ewes were autopsied on day 14 of the cycle. Injections of estradiol significantly reduced luteal weights in both intact and unilaterally hysterectomized ewes. In unilaterally-hysterectomized estradiol-treated ewes corpora lutea on the ovary adjacent to the intact uterine horn were significantly smaller in size than the corpora lutea on the opposite ovary. These latter data suggest that the effect of estradiol on the corpus luteum was mediated at least in part through the adjacent uterine horn. In a third experiment, intramuscular injections of ovine LH (2 mg/day) into intact ewes from day 9 through 13 of the cycle blocked the ability of estradiol (500 µg) injected on each of days 10 and 11 to cause luteal regression. On day 14, corpora lutea of ewes injected with LH and estradiol were significantly heavier and contained more progesterone than glands of ewes treated with estradiol only. Corpora lutea of LH injected ewes, however, contained less progesterone than corpora lutea of control ewes suggesting that the function of the former glands may have been subnormal.