Prostacyclin enhances embryo hatching but not sperm motility

BACKGROUND: Recently we discovered that the human oviduct synthesizes abundant prostacyclin (PGI(2)). Gene knock-out studies suggest that PGI(2) is essential to endometrial decidualization, but the effects of PGI(2) on sperm and embryos have not been reported. METHODS: The effects of PGI(2) on human sperm were analysed by a computer-assisted semen analysis system. The effects of PGI(2) on mouse embryos were examined based on the rates of complete hatching. The expression of PGI(2) receptor (IP) was evaluated by Western blot analysis and immunohistochemistry. The binding of PGI(2) to embryos was confirmed by radioligand binding assay. Finally, cAMP levels were assessed in PGI(2)-challenged embryos. RESULTS: Iloprost (a stable PGI(2) analogue) did not affect the motility or the overnight survivability of human sperm. Western blot analysis did not detect IP in the sperm plasma membrane. In contrast, the hatching of mouse embryos was enhanced by iloprost (ED50 6.7 nmol/l). Exposure to iloprost during 8-cell to morulae or morulae to early blastocyst stages was critical to enhanced hatching. This coincided with the developmental stage-specific expression of IP. Although iloprost bound to blastocysts, it did not significantly increase cAMP. CONCLUSION: PGI(2) enhanced the hatching of mouse embryos but not the motility of human sperm.