Effects of cryopreservation of DNA synthesis in the inner cell mass of in vitro matured/in vitro fertilized bovine embryos frozen in various cryoprotectants.

The rate of DNA synthesis in the inner cell mass (ICM) of frozen-thawed bovine embryos was examined. Bovine blastocysts derived from in vitro matured/in vitro fertilized oocytes were frozen with 1.8 M ethylene glycol (EG), 1.6 M propylene glycol (PG) and 1.4 M glycerol plus 0.25 M sucrose (GL). Viable embryos, after thawing and culture beyond the blastocysts stage, were examined by immunocytochemical staining for detection of DNA synthesis by ICM cells. The numbers of bromodeoxyuridine-immunoreactive ICM cells of frozen-thawed embryos prepared with EG (10.7) and GL (11.5) were significantly lower than those of unfrozen embryos (17.3). The results suggest that the rates of proliferation of ICM cells of frozen-thawed bovine embryos tend to be lower than those of unfrozen embryos irrespective of the cryoprotectant used.