The protective action of polyvinylpyrrolidone-Percoll during the cryopreservation of mouse 2-cell embryos and its effect on subsequent developmental potential post-thaw in vitro and in vivo.

The effects of cryopreservation, in media containing (FS3+) or omitting (FS3) polyvinylpyrrolidone (PVP) in the form of Percoll (PVP-Percoll), on the survival of 2-cell mouse embryos was studied. Survival and zona pellucida disruption post-thaw, growth (assessed by in-vitro culture until the blastocyst stage) and development in vivo (assessed by implantation and living fetus rates and the birth of live progeny) were all investigated. Initial post-thaw survival showed no statistically significant difference (P > 0.05) between FS3+ (91.1 +/- 9.8%) and FS3 (84.5 +/- 6.6%). However, there was a statistically significant (P < 0.05) reduction in the incidence of zona damage when the freezing solution contained PVP-Percoll compared to the control (3.6 +/- 1.0 and 8.7 +/- 0.6% respectively) and a statistically significant (P < 0.05) greater number of embryos developing in vitro to the blastocyst stage (84.8 +/- 7.1 and 72.3 +/- 6.1% respectively). The rates of implantation were not significantly different: 72.2 +/- 7.0% for FS3+ and 51.2 +/- 30.7% for the non-frozen control group. The percentage of live fetuses was also similar between the experimental and control groups: 27.4 +/- 10.6 and 24.3 +/- 11.3% respectively. We conclude that the presence of polymers can protect embryos against cryoinjury and that PVP in the form of PVP-Percoll provides a non-toxic alternative to PVP in its native form, during the cryopreservation of mouse 2-cell embryos.