Survival of rat embryos after freezing.

The effects of cryoprotectants and freeze-thawing procedures on the survival of frozen rat morulae were examined. In the samples frozen and thawed in the presence of DMSO, ethylene glycol or glycerol, higher proportions of the embryos developed into blastocysts in culture when they were frozen slowly (50--71%) than when they were frozen rapidly (20--39%), but the thawing rates of the slowly frozen samples did not affect the viability of the embryos. When erythritol was used as a cryoprotectant, all of the embryos frozen-thawed slowly were killed but rapidly thawed embryos survived regardless of the freezing rate (36--52%). The morulae frozen slowly with ethylene glycol or glycerol and those frozen rapidly with DMSO or erythritol were transferred to recipients after thawing and full-term young were obtained with all 4 cryoprotectants.