IMMUNOCYTOCHEMICAL LOCALIZATION OF ESTROGEN-RECEPTORS IN THE ENDOMETRIUM OF THE EWE

Immunocytochemistry with monoclonal antibodies to the oestrogen receptor (ER) was used to localize ERs in sections of endometrium obtained from cycling and pregnant Corriedale ewes. Representative tissue from Days 4, 10, 14, 15, 16 and 17 of the cycle (Day 0 = onset of oestrus) and Day 15 of pregnancy was used. ER localization was also examined in tissue obtained from ovariectomized (ovex) ewes with and without subcutaneous implants containing oestrogen, progesterone, or oestrogen and progesterone. ER distribution was examined in caruncular endometrium and intercaruncular endometrium. Staining intensity varied according to cell type, stage of the cycle, steroid treatment and pregnancy. No staining was observed in endothelial cells. In all cases, ER was localized within the nuclei of positive cells. Generally, ER levels were high on Day 4 and declined to negligible values by Day 10 (corresponding to peak progesterone values) except in the deep stroma of caruncular endometrium. Positive staining reappeared in stromal cells of caruncles on Day 13 and in the luminal epithelium of intercaruncular tissue on Day 14. Peak intensity was reached on Day 15 for caruncular tissue and Day 16 for intercaruncular tissue. Ovariectomy did not cause an overall reduction in ER levels, whereas treatment with oestrogen and progesterone had variable effects depending on cell type. Progesterone did not suppress overall ER. In Day 15 pregnant tissue, ER was undetectable in all compartments except deep stroma of caruncles, indicating that factors other than progesterone, perhaps embryonic in origin, were responsible. The observation that individual cell types display differential sensitivities to oestrogen and progesterone as regards their expression of ER is consistent with the role of cell-cell interactions as modulators of cellular response to steroids through the oestrous cycle and in pregnancy.