Ultrarapid freezing and thawing of hamster oocytes. Morphologic parameters, trypan blue staining and sperm penetration assay for evaluating survival.

Nine hundred sixteen hamster oocytes were cryopreserved with the ultrarapid freezing method using five different cryoprotective solutions: 3 mol/L dimethylsulphoxide (DMSO) plus 0.25 mol/L sucrose, 3 mol/L DMSO, 3 mol/L propanediol plus 0.25 mol/L sucrose, 3 mol/L propanediol and 10% glycerol. One hundred eighty fresh oocytes served as controls. The viability of the oocytes was evaluated using morphologic parameters, Trypan blue staining and the sperm penetration assay. The viability rates based on morphologic parameters and Trypan blue staining were 82.3%, 65.0%, 51.4%, 33.0% and 0%, respectively, as compared to 100% in the controls. The sperm penetration rates were 27.0%, 0%, 9.8%, 0% and 0%, respectively, as compared to 94-98% in the controls. Our results indicate that among the various cryoprotective solutions used for ultrarapid freezing, 3 mol/L DMSO plus 0.25 mol/L sucrose gave the best results, with a viability rate of 82.3% and a sperm penetration rate of 27%.