Elevated NaCl concentration improves cryotolerance and developmental competence of porcine oocytes

High hydrostatic pressure has been reported to improve the fertilizing or developmental ability of mammalian spermatozoa, oocytes and embryos. This study investigated the effect of another stress, temporarily increased NaCl concentration, on cryotolerance and developmental competence of porcine oocytes. In Experiment 1, survival rates were compared after 1 h exposure to seven elevated NaCl concentrations and 1 h recovery time. In Experiment 2, oocytes were exposed to 593 and 1306 mOsmol NaCl, subsequently recovered, vitrified, then subjected to parthenogenetic activation. Both cleavage and blastocyst rates increased after NaCl treatment compared with untreated controls. In Experiment 3, oocytes were treated with 593 mOsmol NaCl followed by 1 and 2 h recovery, respectively, then used as recipients for somatic cell nuclear transfer (SCNT). Cleavage rates were not different from those in untreated controls, but blastocyst rates increased in both NaCl-treated groups. In conclusion, treatment of porcine oocytes with elevated NaCl concentrations improved their developmental competence after vitrification and parthenogenetic activation or SCNT. Further experiments are required to investigate in-vivo consequences, and the effect on gametes and embryos of different mammalian species.