Gap junction regulation during preterm labor in the rat: multiple effects of the antiprogesterone RU486

The objective of the present study was to examine the effects of the antiprogesterone RU486 on the expression levels of multiple gap junction (GJ) gene products and, in detail, on alpha 1 (connexin43 [Cx43]), in various regions of the rat implantation chamber during experimentally induced preterm labor at mid/late stages of gestation. Vaginal bleeding, but not expulsion of concepti, was observed in a majority of animals 24 h after a single injection of RU486 at Day 15 of gestation, and it persisted until animals were killed 48 h later. The bleeding was completely suppressed by R 5020, a synthetic progesterone with a high affinity for the progesterone receptor (PR). Various components of the implantation chamber (uterus, mesometrial stroma, placenta) and ovaries were isolated 24 and 48 h postinjection and analyzed for alpha 1 (Cx43), beta 1 (Cx32), and beta 2 (Cx26) connexin expression by immunohistochemistry and by Northern blots (alpha 1 only). Alpha 1 Connexin was present at high levels in the myometrium following the inhibition of progesterone action by RU486; accordingly, this effect was completely suppressed by R 5020. The blocking of the PR also had a dramatic effect on expression levels, size, and distribution of junctional plaques composed of beta 1 and beta 2 connexins in polarized luminal and glandular epithelium. The average size of junctional plaques was significantly reduced in the luminal epithelium after RU486 administration. This effect was inhibited in the presence of R 5020. At the RNA level, the alpha 1 transcript was markedly elevated in the uterus and in the ovaries 24 and 48 h after administration of RU486. An elevation was also observed in the mesometrial stroma, while no increase was detected in the placenta. The RU486-induced alpha 1 mRNA steady-state levels in various tissues were completely suppressed by R 5020. These results demonstrate the modulation of multiple connexins in various cell types of the implantation chamber upon blocking of PR action. The expression profile of the myometrial and epithelial GJs was similar to that previously observed in the estrogen-treated rat uterus.