The effects of 1,2-propanediol as a cryoprotectant on the freezing of mouse oocytes

Cryopreservation of mammalian eggs has been successfully accomplished using 1,2-propanediol (PG). Effects of holding times of 0 and 30 min at -40° C and storage times of 1 d and 1 mo at -196° C were investigated in combination with various concentrations of PG (1.0, 1.5, and 2.0M) to determine the survival and fertilizability of mouse oocytes rapidly frozen and thawed in straws. A rapid one-step dilution using 0.5 M sucrose solution inside the straws was used following the thawing of oocytes. A significant effect of PG concentration was found between 1.0 M and 1.5 or 2.0 M (P<0.01), but no significance was discovered between 1.5 M and 2.0 M (P>0.05) on subsequent survival and fertilizability of frozen and thawed mouse oocytes. With 2.0 M PG, the best survival rate (58.3%) and fertilizability rate (19.0%) were obtained by holding at -40° C for 30 min and by storage at -196° C for 1 d. Thirty minutes of holding at -40° C reduced oocyte damage during the procedure but not significantly (P>0.05). In addition, there was no significant difference in the various storage periods (P>0.05). This study demonstrated that mammalian oocytes can be cryopreserved in the presence of 1,2-propanediol by utilizing a rapid freezing and thawing procedure.