Cryopreservation of mature bovine oocytes following centrifugation treatment.

In vitro matured bovine oocytes were frozen slowly in 1.6 M 1,2-propanediol following centrifugation treatment for polarization of lipid droplets in the cytoplasm. After thawing, the survival of the oocytes was assessed morphologically and also by in vitro fertilization and culture. The polarization of cytoplasmic lipid droplets had a negative effect on the survival of frozen-thawed oocytes. Thus, this treatment did not improve the frequency of normal fertilization and development to blastocysts, compared with that of frozen control oocytes. However, the frequency of polyspermy and activation of lipid-polarized oocytes that survived after freezing-thawing and subsequent in vitro fertilization tended to be less than those of surviving control oocytes. In addition, the effect of centrifugation treatment was to produce a small but significant increase in the cleavage rate of oocytes that survived after freezing-thawing and the development rates to blastocysts of surviving lipid-polarized oocytes tended to increase, compared with those of surviving control oocytes. These results suggest that the freezing tolerance of the spindle and other organelles of in vitro matured bovine oocytes is associated with lipid droplets and may be improved by the polarization of cytoplasmic lipid droplets before cryopreservation.