AN IMMUNOHISTOCHEMICAL STUDY ON ESTROGEN RECEPTOR-ALPHA (ER-Α) EXPRESSION IN THE RABBIT UTERUS DURING EARLY PREGNANCY AND PSEUDOPREGNANCY

Estrogen is essential factor for establishment of normal pregnancy in mammals. Estrogenic action in uterus was found to be mediated by intracellular, primarily nuclear receptor called estrogen receptoralpha (ER-α). In the current study; immunohistochemistry was used to localize ER-α in the uterus of pregnant and psudopregnant rabbits. ER-α was strongly expressed in non pregnant uteri in nearly all cellular compartments as luminal and glandular epithelium, stromal cells and myometrial smooth muscle cells. Marked down regulation of the ER-α in luminal but not in glandular epithelium was observed during early periods of pregnancy and pseudopregnancy. Weaker glandular staining was only observed during postimplantation periods. Stromal cells were always immunopositive even after implantation till day twelve of pregnancy. Myometrium was expressing the receptor till after implantation. ER-α was always nuclear in immunopositive cells. Our results revealed that, ER-α was involved in the process of progestational proliferation in the rabbit uterus; in addition, the receptor expression is tissue specific and maternally controlled. An Immunohistochemical Study On Estrogen Receptor-Alpha (Er-Α) Expression . Atif Hasan Kafr El-Sheikh Vet.Med.J. Vol. 1 No.1 (2003) 57 INTRODUCTION Estrogen hormone is important for normal preimplantation uterine changes and embryonic development in the reproductive tract (Weitlauf, 1994). It is thought that estrogen regulates the female reproductive functions primarily through the nuclear estrogen receptor alpha (ER-α). After hormone binding become the ER-α activated and serve as a transcription factor that modulates the expression of target genes (Beato, 1989; Das et al., 1997; Rissman et al., 1997). During early pregnancy, ER-α was immunohistochemically localized in smooth muscles of uterine arteries in both human and rabbit uteri (Perrot-Applant et al., 1988). ER-α was observed in the decidual cells of primates (baboon) (Hild-Petito et al., 1992) and human (Wang et al., 1992). On the other hand, the ER-α was shown to be down regulated in uterine luminal and glandular epithelium after implantation and during late pregnancy in human (Wu et al., 1993) in cat (Li et al., 1992) and in pig (Geisert et al., 1993). During Preimplantation period, the endometrium in rabbit undergo progestational proliferation in correlation with a high serum level of estrogen (Davies and Hoffman, 1973) which reach a peak value during the first week of gestation in rabbit (Challis et al., 1973 ; Kriesten and Murawski, 1988). As the rabbit is an induced ovulator animal; the uterine changes could be exactly recorded in relation to days of pregnancy considering day 0 (estrous stage) is the day of mating or treatment with hCG (human Chorionic Gonadotropin). An Immunohistochemical Study On Estrogen Receptor-Alpha (Er-Α) Expression . Atif Hasan Kafr El-Sheikh Vet.Med.J. Vol. 1 No.1 (2003) 58 The rabbit is a laboratory animal model and has economic value as well; studying of rabbit reproduction is of great importance. Moreover a detailed study on the expression of ER-α during the preimplantation period in rabbit uterus was not carried out before. The current study demonstrate immunohistochemically, the expression of ER-α in the uteri during preimplantation period of both pregnant and pseudopregnant rabbits. MATERIALS AND METHODS