CSIRO Publishing Acta Medica Okayama 1031-3613 28 6 2014 Endothelin as a local regulating factor in the bovine oviduct 673 681 EN Yuki Yamamoto Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University Misa Kohka Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University Yoshihiko Kobayashi Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University Izabela Woclawek-Potocka Department of Reproductive Immunology and Pathology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences Kiyoshi Okuda Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University Endothelin (EDN) is a possible regulating factor of oviductal motility, which is important for the transport of gametes and embryo. To clarify the factors that control the secretion of EDN in the bovine oviduct, the expression of EDNs, EDN-converting enzymes (ECEs) and EDN receptors (EDNRs) were investigated. All isoforms of EDN (EDN1-3), ECE (ECE1 and ECE2) and EDNR (EDNRA and EDNRB) were immunolocalised in the epithelial cells of the ampulla and the isthmus. EDNRs were also immunolocalised in smooth-muscle cells. The mRNA expression of EDN2 and ECE2 was higher in cultured ampullary oviductal epithelial cells than in isthmic cells. The expression of EDN1, EDN2 and ECE2 in the ampullary tissue was highest on the day of ovulation. Oestradiol-17β increased EDN2 and ECE1 expression, while progesterone increased only ECE1 expression in cultured ampullary epithelial cells. These results indicate that EDNs are produced by epithelial cells and their target site is smooth-muscle and epithelial cells, and suggest that ovarian steroids are regulators of endothelin synthesis in ampullary oviductal epithelial cells. No potential conflict of interest relevant to this article was reported.