Effects of ovarian steroids on uterine growth, morphology, and cell proliferation in ovariectomized, steroid-treated ewes.

Uterine growth, morphology, and endometrial cell proliferation were evaluated in intact estrous (EST; Day 0 of the estrous cycle) or luteal (LUT; Day 10 of the estrous cycle) ewes or in ovariectomized ewes receiving no hormone (OVX); estradiol-17beta (OVX+E); progesterone for 8 (OVX+P8), 30 (OVX+P30), or 60 (OVX+P60) days; estradiol followed by progesterone (OVX+E+P); or progesterone followed by estradiol (OVX +P+E). Uterine weights were greater for EST than for LUT ewes, were reduced 2- to 4-fold in OVX ewes, and were increased in estradiol-treated (OVX+E, OVX+E+P, and OVX+P+E) ewes. The effects of estradiol treatment on uterine growth in OVX ewes were primarily on cellular hypertrophy rather than hyperplasia. Endometrial labeling index (LI) was greater for EST than for LUT ewes and was low in OVX ewes. Compared with OVX ewes, OVX+E and OVX+P+E ewes had increased LI for all endometrial tissues, whereas OVX+P8 and OVX+E+P ewes had increased LI only for luminal epithelium. These data will help us determine the mechanisms by which ovarian steroids regulate uterine growth in ewes.