Two-step freezing of two-cell rabbit embryos after partial dehydration at room temperature

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Abstract
The effect of rapid freezing and thawing on the survival of 2-cell rabbit embryos was examined. When embryos in 2.2 M-propanediol were directly plunged from room temperature to liquid nitrogen some of them survived after thawing (8%) but only if they had been pretreated by exposure to an impermeable solute, sucrose, that makes the blastomeres shrink osmotically before cooling. High survival (77-88%) in vitro was obtained when pretreated embryos were first held at -30.degree. C for 30-240 min before immersion into liquid nitrogen. Transfer of such frozen-thawed embryos gave a survival rate to live young similar to that obtained with controls (26 and 32%, respectively). DMSO [dimethylsulfoxide] was less effective than propanediol; only 2 out of 38 sucrose-pretreated frozen-thawed embryos developed in vitro. A combination of partial dehydration of blastomeres at room temperature with their permeation by a cryoprotective agent offers a simple method for successful rapid freezing and thawing of rabbit embryos.