Rapid freezing of rabbit embryos has a negative effect on embryo morphology

Rabbit embryos were obtained in vivo at 2-cell, 8-16-cell, compacted morula and early blastocyst stages. Embryos were cultured until reaching the expanded blastocyst stage after applying a procedure of rapid freezing by a two-step cooling method, either after exposure to a cryoprotectant solution or immediately after their recovery (control). The procedure of rapid freezing implied exposure of the embryos to a solution composed by dimethylsulphoxide (DMSO, 3.5mo1/l) and sucrose (0.25mol/l) for 2.5 min at room temperature, followed by a period of 30-45 min at -27°C before plunging into liquid nitrogen (two-step cooling). Then, rapid thawing and multi-step dilution of the cryoprotectants were performed. Embryo development was monitored during subsequent culture and the morphological differences between groups were evaluated. The morphological parameters analyzed were the timing of embryo development until reaching the expanded blastocyst stage, the diameter and the number of cells of the expanded blastocysts obtained after culture in vitro. The results of this study show that the frozen-thawed embryos reached the expanded blastocyst stage later than the control embryos and the expanded blastocysts obtained from frozen-thawed embryos had a smaller diameter and number of cells than those from control and exposed embryos. © 1997 Blackwell Wissenschafts-Verlag, Berlin.