Hormonal control of arylhydrocarbon receptor (AhR) expression in the preimplantation rabbit uterus

We show that the arylhydrocarbon receptor (AhR) is localised in a distinct pattern in the preimplantation rabbit uterus. Employing immunohistochemistry, uteri from mature and immature rabbits were studied in different pregnancy stages during the preimplantation period (non-pregnant/estrous, pregnant and pseudopregnant) and following treatment with estradiol and progesterone, respectively. The staining patterns in pregnant and pseudopregnant rabbits were similar, indicating a primary maternal control of expression. A distinct change in AhR localization occurred in the endometrium of (1) non-pregnant compared with pregnant rabbits and (2) shortly prior to the anticipated time of implantation. Compared with non-pregnant uteri, the AhR was no longer restricted to a small cytoplasmic area apical to the nucleus but was found in the entire cytoplasm and in the nuclei of the endometrial epithelial cells in pregnant uteri. Prior to implantation, at day 6, stromal cells and the epithelium of the uterine glands, but no longer the luminal epithelial cells, were immunopositive. The estradiol-treated immature uteri showed a strong expression in the luminal epithelium and in some uterine glands, often with nuclear staining, while the estradiol-primed and progesterone-treated specimens had a similar staining pattern as mature preimplantation uteri. Present results demonstrate a distinct localization pattern of the AhR in the endometrium during the preimplantation period. Stage-specific changes in the expression pattern indicate control of AhR expression by maternal steroid hormones.