Estrogen receptor beta, but not estrogen receptor alpha, is present in thevascular endothelium of the human and nonhuman primate endometrium

Estrogen action is dependent upon the presence of specific ligand-activated receptors in target tissues. The aim of the present experiments was to com pare the spatial and temporal pattern of expression of estrogen receptor be ta (ER beta) with that of ER alpha in full thickness endometrial samples (f rom the superficial to the basal zone) obtained from both women and rhesus macaques. Immunohistochemical localization with specific antibodies reveale d that ER alpha and ER beta were both expressed in nuclei of the glands and stroma. Consistent with previous studies, expression of ER alpha declined in the glands and stroma of the functionalis during the secretory phase. Th e luminal epithelium also displayed positive immunoreactivity for ER beta. Expression of ER beta declined in glandular cell nuclei, but not stroma, wi thin the functionalis during the late secretory phase. Levels of expression of ER alpha and ER beta in all cellular compartments remained unchanged in the basalis. Both receptor subtypes were detected on Western blots using p roteins extracted from uterine samples obtained throughout the menstrual cy cle. There was a striking contrast between the pattern of expression of ER alpha and ER beta in the vascular endothelium and the perivascular cells surroun ding endometrial blood vessels; only ER beta was present in the endothelial cell population, although bath forms of ER were expressed in perivascular cells. We conclude that estrogen action(s) within the vascular endothelium in the endometrium may be mediated via direct binding to the ER beta isofor m and that these cells could therefore be a target for agonists or antagoni sts that selectively target the beta form of the ER.