IMMUNOCYTOCHEMICAL ANALYSIS OF ESTROGEN AND PROGESTIN RECEPTORS IN UTERI OF STEROID-TREATED AND PREGNANT CATS

The purpose of this study was to determine the distribution of estrogen receptors (ER) and progestin receptors (PR) in specific uterine cell populations during various steroid hormone treatment regimens, and to determine if ER and PR distribution in the uterus is altered during implantation and the establishment of pregnancy in the cat. The tissues were processed for indirect inununocytochemical localization of receptors using specific monoclonal antibodies against ER and PR. ER were present in the nuclei of all epithelial cells and stromal fibroblasts in endometrium obtained from ovariectomized animals, whereas PR were only detectable in the nuclei of stromal fibroblasts. There was an apparent increase in the staining intensity and number of nuclei that stained positively for both ER and PR in all cell populations after 14 days of estradiol treatment. The administration Of progesterone for 14 and 21 days, in the presence or absence of continuous estradiol, reduced the apparent intensity of staining and the number of nuclei staining positively for both ER and PR. ER were undetectable in the luminal epithelium, but remained in the glandular epithelial cells and stromal fibroblasts, whereas PR were only detectable in stromal fibroblasts. ER and PR localization in the endometrium obtained from estrus animals was similar to that observed in the estradiol-treated animals. A general decrease in intensity of staining for both ER and PR was evident by Day 5 postcoitus in pregnant animals. This decrease in intensity of staining continued until Day 12 postcoitus, when the distributions of ER and PR were similar to those observed in the ovariectomized estradiol-primed, progesterone-treated animals. This same staining pattern was maintained in both the implantation and non-implantation site endometrium during the period of time when the placenta was established. ER and PR were undetectable in all cell populations of the placenta. The nuclei of the myometrial smooth muscle cells in all stages of pregnancy contained ER and PR. This study shows that estradiol and progesterone are the primary regulators of ER and PR expression in uterine cells of the cat, that ER and PR are maintained in the nuclei of specific cell types after long-term exposure to exogenous or endogenous progesterone, and that the process of implantation does not alter the distribution of ER and PR in the pregnant cat uterus.