Cryopreservation of immature buffalo oocytes: effects of cytochalasin B pretreatment on the efficiency of cryotop and solid surface vitrification methods.

The aim of the present study was to compare the efficiency of the solid surface (SSV), cryotop (CT) vitrification methods and cytochalasin B (CB) pretreatment for cryopreservation of immature buffalo oocytes. Cumulus-oocyte complexes (COCs) were placed for 1 min in TCM199 containing 10% dimethylsulfoxide (DMSO), 10% ethylene glycol (EG), and 20% fetal bovine serum, and then transferred for 30 s to base medium containing 20% DMSO, 20% EG and 0.5 mol/L sucrose. CB pretreated ((+)CB) or non-pretreated ((-)CB) COCs were vitrified either by SSV or CT. Surviving vitrified COCs were selected for in vitro maturation (IVM) and in vitro fertilization (IVF). The rate of viable oocytes after vitrification in CT groups (82%) was significantly lower (P < 0.05) than that in a fresh control group (100%), but significantly higher (P < 0.05) than those in SSV groups (71-72%). Among vitrified groups, the highest maturation rate was obtained in the CT (-)CB group (32%). After IVF, the cleavage and blastocyst formation rates were similar among vitrified groups but significantly lower than those of the control group. In conclusion, a higher survival rate of oocytes after vitrification and IVM was obtained in the CT group compared with that in the SSV group, indicating the superiority of the CT method. Pretreatment with CB did not increase the viability, maturation or embryo development of vitrified oocytes.