An immunohistochemical study on the regulation of estrogen receptor <formula notation="TeX">$\alpha$</formula> by estradiol in the endometrium of the immature ewe

The effects of estradiol-17<formula notation="TeX">$\beta$</formula> (E2) on the expression of estrogen receptor <formula notation="TeX">$\alpha$</formula> (ER<formula notation="TeX">$\alpha$</formula>) in stromal and epithelial cells of endometrium in prepubertal lambs were investigated. Twenty three-month-old lambs were treated or not treated with one, two or three i.m. injections of E2 (1 <formula notation="TeX">$\mu$</formula>g<formula notation="TeX">$\cdot$</formula>kg<formula notation="TeX">$^{-1}$</formula>) in corn oil at intervals of 24 h. Lambs were slaughtered 12 or 24 h after the last injection. An immunohistochemical technique was used to visualize ER<formula notation="TeX">$\alpha$</formula> immunostaining which was then analyzed quantitatively by a computer imaging analysis system. Seven endometrial compartments defined by cell type and location were analyzed separately. Positive staining of ER<formula notation="TeX">$\alpha$</formula> was seen in the nuclei of stromal and epithelial cells. Glandular epithelium located next to the myometrium was stained more intensely than that next to the luminal epithelium and this phenomenon was maintained during treatment. Significantly less immunostaining was found in stromal cells 12 and 24 h after the first injection compared to the control group. A similar pattern was found in the glandular epithelium, although the decrease was more pronounced and the restoration of ER<formula notation="TeX">$\alpha$</formula> was faster. This study shows that E2 treatment down regulates ER<formula notation="TeX">$\alpha$</formula> in the endometrium temporarily in both stromal and epithelial cells, but the characteristics of this effect seems to be cell type specific.