Vitrification of rat blastocysts developed in vitro

Approximately 50% of rat 8-cell embryos obtained from the oviduct on day 4 of pregnancy developed to the blastocyst stage after 18 of incubation in vitro. The embryos were compared with in vivo blastocysts derived from the uterus on day 5 of pregnancy as regards their response to vitrification treatment. Before vitrification, both types of embryos were exposed to vitrification solution, and subsequent embryonic development was inhibited with increasing time of exposure. A greater suppression of development after exposure was observed in the embryos cultured in vitro compared with in vivo blastocysts. However, development was gradually restored as in vitro incubation was continued. The response of embryos to vitrification and warming treatments was shown to be almost the same for both in vitro and in vivo blastocysts, though the former were significantly (p < 0.05) less tolerant of exposure to vitrification solution. These results suggest that in vitro blastocysts were much more susceptible to vitrification solution than in vivo blastocysts. The degree of damage caused by vitrification and thawing treatments, and the inhibition of in vitro embryonic development, were significantly (p < 0.05) more serious for in vitro blastocysts.