Vitrification of mouse oocytes in ethylene glycol-raffinose solution:: Effects of preexposure to ethylene glycol or raffinose on oocyte viability

We investigated the effects of preexposure to ethylene glycol (EG) or raffinose on the viability of vitrified mouse oocytes. Ovulated oocytes at the metaphase II stage were preexposed either to 2 M EG for 0, 2, or 5 min or to ascending concentrations (0.15 followed by 0.3 M) of raffinose solution for 2, 5, or 10 min each (here referred to as 2-2,5-5, and 10-10 min, respectively). The oocytes were then exposed to a vitrification solution (VS), 6 M EG + 0.3 M raffinose, for 0.5, 1, 2, or 5 min and then vitrified or immediately diluted. After warming, the developmental capacity of oocytes was determined after irt vitro fertilization. Volume changes in oocytes during preexposures and exposure to the VS were also investigated. The results demonstrated that preexposure to 2 M EG allowed shorter exposure times of oocytes to the VS and that predehydration in raffinose solutions for 5-5, but not 2-2 or 10-10 min, allowed a wider range of exposure times to the VS. Experiments on volume change suggested that the optimum time of exposure to the VS depends on the amount of EG permeation after preexposure to 2 M EG or to raffinose solutions. Preexposures to 2 M EG or raffinose under optimized conditions increased thc viability of vitrified-warmed oocytes compared to direct exposure to VS without preexposures. (C) 2001 Academic Press.