High survival of mouse embryos after rapid freezing and thawing inside plastic straws with 1–2 propanediol as cryoprotectant

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Abstract
A method for obtaining a high survival rate of frozen-thawed mouse embryos is presented. Eight-cell mouse embryos were frozen inside small plastic straws in the presence of 1–2 propanediol and stored at −196°C. After thawing, the embryos were diluted for only 5 min in a 1.0 M sucrose solution to remove the 1–2 propanediol from the cells. At high rate of thawing (∼2500°C/min) more than 88% of the embryos survived in vitro to the blastocyst stage provided that the dilution of propanediol was performed rapidly during thawing. At a lower rate of thawing (∼300°C/min), survival tended to be higher (94.7%) when dilution was done 5 min after thawing. When the frozen-thawed embryos were transferred to the oviducts of day 1 pseudopregnant recipients either directly after the dilution of 1–2 propanediol or after 24 or 48 hr of culture, a high proportion of them (65.9%) develop normally to viable fetuses.