Osmotic stress induced by sodium chloride, sucrose or trehalose improves cryotolerance and developmental competence of porcine oocytes.

Exposure of porcine oocytes to increased concentrations of NaCl prior to manipulation has been reported not only to increase cryotolerance after vitrification, but also to improve developmental competence after somatic cell nuclear transfer (SCNT). In the present study we compared the effects of NaCl with those of concentrated solutions of two non-permeable osmotic agents, namely sucrose and trehalose, on the cryotolerance and developmental competence of porcine oocytes. In Experiment 1, porcine in vitro-matured cumulus-oocyte complexes (COCs; n = 1200) were exposed to 588 mOsmol NaCl, sucrose or trehalose solutions for 1 h, allowed to recover for a further 1 h, vitrified, warmed and subjected to parthenogenetic activation. Both Day 2 (where Day 0 is the day of activation) cleavage and Day 7 blastocyst rates were significantly increased after NaCl, sucrose and trehalose osmotic treatments compared with untreated controls (cleavage: 46 +/- 5%, 44 +/- 7%, 45 +/- 4% and 26 +/- 6%, respectively; expanded blastocyst rate: 6 +/- 1%, 6 +/- 2%, 7 +/- 2% and 1 +/- 1%, respectively). In Experiment 2, COCs (n = 2000) were treated with 588 mOsmol NaCl, sucrose or trehalose, then used as recipients for SCNT (Day 0). Cleavage rates on Day 1 did not differ between the NaCl-, sucrose-, trehalose-treated and the untreated control groups (92 +/- 3%, 95 +/- 3%, 92 +/- 2% and 94 +/- 2%, respectively), but blastocyst rates on Day 6 were higher in all treated groups compared with control (64 +/- 2%, 69 +/- 5%, 65 +/- 3% and 47 +/- 4%, respectively). Cell numbers of Day 6 blastocysts were higher in the control and NaCl-treated groups compared with the sucrose- and trehalose-treated groups. In conclusion, treatment of porcine oocytes with osmotic stress improved developmental competence after vitrification combined with parthenogenetic activation, as well as after SCNT.