REGULATION OF CONNEXIN26 AND CONNEXIN43 EXPRESSION IN RAT ENDOMETRIUMBY OVARIAN-STEROID HORMONES

A distinct spatial and temporal pattern of connexin26 and connexin43 ( cx26 and cx43) expression was observed in the rat endometrium in respo nse to embryo implantation; however, connexin expression was suppresse d during the preimplantation period. Pseudopregnant rats did not show connexin mRNA, while artificial decidualization induced by a scratch l ed to a strong expression of cx2G and cx43 in the endometrium of these animals. In order to examine the regulatory effects of ovarian steroi d hormones on connexin expression, ovariectomized rats were treated wi th progesterone (P) and/or estradiol-17 beta (E(2)). Untreated, ovarie ctomized animals expressed mRNA for cx43, but not for cx26. Endometria l expression of mRNA for both connexins was strongly enhanced by E(2) treatment; immunolabeling revealed protein for cx2G in the uterine lum inal epithelial cells and for cx43 in the uterine stromal cells. P tre atment, either alone or in combination with E(2), suppressed expressio n of connexin mRNA. P suppression in the presence of E(2) was reversib le when P was withdrawn. When administered on Days 0-2 of pregnancy, t he antiprogestin onapristone inhibited the effect of P and gave rise t o strong expression of both connexin transcripts. These results demons trate that expression of cx26 and cx43 in the rat uterine endometrium is differentially regulated by E(2) and P during early pregnancy.