IMMUNOCYTOCHEMICAL LOCALIZATION OF ESTROGEN AND PROGESTIN RECEPTORS IN THE BABOON (PAPIO-ANUBIS) UTERUS DURING IMPLANTATION AND PREGNANCY

Although estrogen and progesterone are essential for the establishment of pregnancy in primates, localization of their specific receptors in uterine cell types during pregnancy has not been investigated. Theref ore, uteri were obtained from baboons during the menstrual cycle, afte r steroid treatment, or during early pregnancy on days 18, 25 and 32 p ostovulation. Uterine and placental tissues were also collected from b aboons during late pregnancy. Tissues were processed for indirect immu nocytochemical localization with specific monoclonal antibodies agains t estrogen receptor (ER; H222) and progestin receptor (PR; JZB39). Ide ntification of specific cell types was confirmed by iron-hematoxylin/v an Gieson and Gimori's stains. Specific staining for steroid receptors was detected only in the nucleus. In the absence of ovarian steroid h ormones (ovariectomized baboons), ER were present in glandular epithel ium, stroma, and myometrial smooth muscle cells (SMC). In contrast, PR were absent from all uterine cell types. In the estrogen-dominated (f ollicular and estradiol treatment) uterus, ER and PR were detected in the nuclei of glandular and surface epithelium, stroma, and myometrial SMC. Elevated progesterone levels (luteal or after progesterone treat ment) resulted in a loss of nuclear ER in stroma and epithelium, excep t in the deep glandular epithelium in the basalis. PR was maintained i n the stroma throughout the endometrium, but was detected only in the epithelium of the deep glands. The myometrial SMC contained both ER an d PR. In early pregnancy, ER was absent from the glands and stroma as early as day 18 postovulation, but was present in the wall of spiral a rteries, blood vessels, and myometrial SMC. On day 18 postovulation, s taining for PR was absent from all glandular epithelium, but was maint ained in the stroma surrounding the glands and spiral arteries, the wa ll of spiral arteries, blood vessels, and myometrial SMC. Stroma away from glandular epithelium contained few PR-positive cells. This staini ng pattern persisted throughout early pregnancy. No apparent differenc es in ER and PR localization were evident between the implantation and nonimplantation sites of the endometrium and myometrium. In late preg nancy, ER were only present in the SMC of the myometrium; however, PR were detected in stroma and myometrial SMC. The maternally derived dec idua expressed PR, but not ER, in the majority of cells. In contrast, fetally derived tissues, placenta, and amnio-chorion, did not contain either ER or PR at any stage of pregnancy. Clearly, ER and PR persist in particular uterine cell compartments despite the continual high lev els of progesterone in pregnancy and, thus, support a receptor-mediate d mechanism for estrogen and progesterone regulation of implantation a nd pregnancy.