Estrogen and Progestogen Receptors in the Implantation Sites and Interembryonic Segments of Rat Uterus Endometrium and Myometrium

Estrogens play a central role in the mechanism of blastocyst implantation. Whether the blastocyst itself contributes to this hormonal effect by locally releasing estrogens at the site of implantation remains debatable. Indirect evidence of estrogen production by the embryo could be obtained if specific estrogenic effects were found to a greater extent at the implantation sites, when compared to the interembryonic segments. Six-day pregnant rats were injected in the morning with Evans’ blue, and the uterine blue stripes revealing the implantation sites were separated from the interembryonic segments. Endometrial and myometrial portions of the two sites were separately pooled and analyzed for protein, estradiol receptor (E2R) and progesterone receptor (Prog.R) contents, in cytosol and nuclear fractions. The present results show a significantly higher protein concentration in cytosol of endometrium (20 ± 6.2 vs. 12 ± 7.6) (means ± sd) and, to a lesser extent, in the cytosol of myometrium (10 ± 2.5 vs. 8.1 ± ...