Steroid hormone effects on intracellular communication between term pregnant human myometrial cells before labor

The appearance of gap junctions (GJs) between myometrial smooth muscle cells is one of the major events associated with the onset of labor. We have employed dye-coupling and electrical-current injection techniques to study the mechanisms by which steroid hormones regulate Gls in term pregnant myometrium of women before labor. Progesterone (P-4) did not alter the input resistance (R(o)) of the tissues when added to Tyrode's solution, which was used as control treatment. Octanol, the putative gap junctional uncoupling agent, increased the R(o) of the cells compared to the control and P-4-treated groups. The membrane potential (E(m)) did not differ between these groups, However, when P-4 was applied after the tissue was perfused with estradiol (E(2)), the results changed dramatically: the E(m) hyperpolarized, and the R(o) increased. Octanol increased the R(o) in E(2)-treated tissues, but did not affect the E(m). Consecutive application of E(2), octanol, E(2), and P-4 resulted in rapid changes in the R(o) of the cells. Dye-coupling was mostly detected between cells from controls and E(2)-treated tissues. These results indicate that P-4 exerts its effects in the presence of E(2) and that P-4 has rapid effects on the intercellular communication between human myometrial cells.