Changes in Nuclear Estradiol Receptor and Cell Structure During Estrous Cycles and Pregnancy in the Oviduct and Uterus of Cats

Oviducts and uteri were removed from cats at various intervals during the estrous cycle and pregnancy. Systemic blood was drawn on the day the tissues were removed and plasma estradiol (E2) and progesterone (P) were measured by radioimmunoassay. The amounts of nuclear E2 receptor in the oviducts and uteri were determined with an exchange assay; portions of these same organs were fixed and embedded in Araldite for morphological study. In both the oviduct and uterus, the content of nuclear E2 receptor is low in anestrus, rises significantly during proestrus and estrus (E2-dominated) and then declines significantly during pregnancy (P-dominated). During the estrous phases of the cycle, the oviducts become hypertrophied, fully ciliated and secretory; during pregnancy these organs atrophy, deciliate and stop secreting. The epithehium of the endometrial glands also hypertrophies during the estrous phases of the cycle; during pregnancy, hyperplasia, further hypertrophy, glycogen deposition and formation of unique basophilic granules characterize the progestational response in this species. Thus, although both uterus and oviduct are depleted of nuclear E2 receptor during pregnancy, the endometrial glands hypertrophy and show altered and heightened secretion while the oviduct atrophies and dedifferentiates