An immunohistochemical study on the regulation of estrogen receptor alpha by estradiol in the endometrium of the immature ewe.

The effects of estradiol-17beta (E2) on the expression of estrogen receptor alpha (ERalpha) 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 microg x kg(-1)) 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 ERalpha 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 ERalpha 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 ERalpha was faster. This study shows that E2 treatment down regulates ERalpha in the endometrium temporarily in both stromal and epithelial cells, but the characteristics of this effect seems to be cell type specific.