Immunohistochemical analysis of estrogen receptor alpha, estrogen receptor beta and progesterone receptor in normal human endometrium

The endometrium expresses estrogen (ER) and progesterone receptors (PR), which are involved in autocrine and paracrine regulation processes in response to estrogen and progesterone. The aim of the present study was to evaluate immunohistochemical distribution patterns of estrogen receptor alpha (ERα), estrogen receptor beta (ERβ) and PR in normal human endometrial tissue with the use of monoclonal antibodies. Human endometria were obtained from 17 premenopausal patients undergoing surgery for non-malignant diseases and were classified to be in proliferative, early secretory and late secretory phases by histological and anamnestical means. Distribution patterns of the steroid receptors were evaluated using the IRS-score and the Mann–Whitney rank-sum test was used to compare the means. Correlation was assessed with the Spearman factor and linear regression analysis. ERα and PR expression decreased significantly (p<0.05) in glandular epithelium from the proliferative to the late secretory phase. ERβ expression showed a similar significant decrease (p<0.05), although staining intensity was lower than that of ERα. A significant correlation between expression of all three steroid receptors was observed (p<0.001). Distribution patterns of ERα, ERβ and PR in normal human endometrium showed a cyclic variation during the menstrual cycle. A significant correlation between expression of ERα, ERβ and PR was also demonstrated using regression analysis, indicating dependence of expression of these three steroid receptors. The present study shows the presence of steroid receptors in human endometrial epithelium, indicating that these cells respond to estrogen and progesterone and thus playing a significant role in endometrial physiology.