Identification of gap junctions in the oviduct and regulation of connexins during development and by sexual hormones.

Gap junctions in epithelial cells of the oviduct were identified by immunohistochemistry and Western blotting. Immunohistochemical studies showed that rat, hamster, mouse, and human oviducts contained connexin26 and connexin43 but not connexin32. The content of both connexins in the oviduct depended on the cell type, state of maturation and hormone status. During ontogeny, the epithelial and smooth muscle cells of immature rat oviducts (< 30 days) contained a low amount of connexin43, and connexin26 was undetectable. In mature oviducts (> 30 days), however, connexin26 was detected only in the isthmus and in localized regions of the ampullar epithelial layer. Moreover, at this age, the amount of connexin43 was high in both cell strata throughout the entire organ. During the estrous cycle, levels of connexin43 in the isthmic but not in the ampullar segment were higher in the proestrous and estrous day than at diestrous days. In addition, estrogen treatment produced a significant increase in total and phosphorylated isoforms of connexin43 levels in oviducts of pregnant rats. The estrogen effect was prevented by the simultaneous administration of progesterone which by itself did not affect the levels of connexin43. The high content of connexins found between oviductal cells as well as their responsiveness to hormone regulation, suggest that gap junctions might be involved in coordinating oviductal cell functions such as smooth muscle contraction and epithelial ciliary beat.