HIGH-RATES OF SURVIVAL AND FERTILIZATION OF MOUSE AND HAMSTER OOCYTESAFTER VITRIFICATION IN DIMETHYLSULFOXIDE

A high proportion (> 70%) of mouse and hamster oocytes exposed for 3-5 min to 1.5 M dimethylsulfoxide (DMSO) and washed briefly in 3.9 M DMS O before vitrification in 6.0 M DMSO appeared morphologically normal o n recovery. Significantly fewer (< 46%) mouse oocytes appeared normal when the time of exposure to 1.5 M DMSO was reduced to 1 min or less. The rate of fertilization in vitro of vitrified oocytes was reduced co mpared to the rate for untreated controls (mouse: 79% vs. 94%; hamster : 73% vs. 87%). After removal of the zona pellucida, fertilization was similar in vitrified and control hamster oocytes inseminated with ham ster (> 90%) or human (21% vs. 23% ) sperm. Sperm nuclear decondensati on and pronuclear formation appeared to be delayed in the cytoplasm of vitrified hamster oocytes. Seventy-nine percent of 2-cell-stage mouse embryos derived from vitrified oocytes implanted after transfer to ps eudopregnant recipients, but only 40% developed to normal fetuses comp ared to 61% of controls. The reason for this high rate of postimplanta tion loss is unknown.