EFFECTS OF STIMULATION OR INHIBITION OF LIPID-PEROXIDATION ON FREEZING-THAWING OF MOUSE EMBRYOS

This study was conducted to determine whether the tolerance of embryos to the stress of free modified by including in the incubation medium stimulators or inhibitors of membrane lipid peroxidation. Mouse zygote s were cultured in medium M16, supplemented or not with FeSO4, apotran sferrin, and/or ascorbate. In each culture supplement, 8-cell embryos were randomly allocated to an untreated (nonfrozen) control group, or treatment by freezing using slow or ultrarapid cooling. In the slow-fr ozen group, FeSO4 (49.3%, 66 of 134), decreased embryo survival, where as apotransferrin (82.7%, 110 of 133) and ascorbate (86.4%, 114 of 132 ), increased significantly the percentage of intact embryos recovered after thawing compared to those cultured in the basic medium M16 (66.9 %, 99 of 148). Apotransferrin and ascorbate also increased significant ly the percentage of blastocysts on Day 5 (79.7%, 106 of 133, and 89.4 %, 118 of 132 vs. 62.2%, 92 of 148, respectively). Ascorbate, in addit ion, increased significantly the percentage of implantations compared to those in the basic medium M16 (84.5%, 60 of 71 vs. 61.1%, 37 of 56) . Changes in the ultrarapidly frozen group were not so evident. Howeve r, a significant fetal wastage after implantation was observed when em bryos were cultured without additives and then ultrarapidly frozen (31 .7%, 13 of 41 vs. 7.0%, 3 of 43, in the nonfrozen control group). Feta l weight was similar between culture conditions, but it was significan tly lower in slow-frozen and ultrarapidly frozen embryos than in the n onfrozen control group. These data indicate that embryo tolerance to t he freezing-thawing stress can be modified by incubating the embryos i n the presence of stimulators or inhibitors of membrane lipid peroxida tion. This effect is more evident in embryos cryopreserved by slow coo ling than by ultrarapid freezing techniques.