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 m orula and early blastocyst stages. Embryos were cultured until reachin g the expanded blastocyst stage after applying a procedure of rapid fr eezing by a two-step cooling method, either after exposure to a cryopr otectant solution or immediately after their recovery (control). The p rocedure of rapid freezing implied exposure of the embryos to a soluti on composed by dimethylsulphoxide (DMSO, 3.5 mol/l) and sucrose (0.25 mol/l) for 2.5 min at room temperature, followed by a period of 30-45 min at -27 degrees C before plunging into liquid nitro gen (two-step c ooling). Then, rapid thawing and multi-step dilution of the cryoprotec tants were performed. Embryo development was monitored during subseque nt culture and the morphological differences between groups were evalu ated. 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 cu lture in vitro. The results of this study show that the frozen-thawed embryos reached the expanded blastocyst stage later than the control e mbryos and the expanded blastocysts obtained from frozen-thawed embryo s had a smaller diameter and number of cells than those from control a nd exposed embryos.