POSTTHAW VIABILITY OF THE INNER CELL MASS OF IN VITRO-MATURED IN VITRO-FERTILIZED BOVINE EMBRYOS FROZEN IN VARIOUS CRYOPROTECTANTS

A study was conducted to examine the viability of inner cell mass (ICM ) cells of frozen-thawed in vitro-matured (IVM)/in vitro-fertilized (I VF)-derived embryos using various cryoprotectants. Expanded blastocyst s were frozen and thawed in 1.4 M glycerol with 0.25 M sucrose (GL), 1 .6 M propylene glycol (PG), 1.8 Methylene glycol (EG), or 1.3 Methylen e glycol monomethyl ether (EME) as cryoprotectants using a one-step me thod. After thawing, the embryos were cocultured for 24 h with cumulus cells in TCM199. Embryos which were viable after thawing and develope d beyond the blastocyst stage were treated by immunosurgery and differ ential fluorochrome staining for ICM cell counts. Overall, there were no significant differences in the development to blastocyst stage afte r 24 h culture in each cryoprotectant (P < 0.05, chi(2) analysis). The viability of ICM cells of frozen-thawed embryos with each cryoprotect ant was lower (GL, 72.7%; PG, 67.8%; EG, 77.5%; EME, 74.7%) than that of unfrozen embryos (84.4%). In the case of PG as a cryoprotectant, vi ability of ICM cells was significantly lower than that of unfrozen emb ryos (P < 0.05, ANOVA analysis). Our results suggest that the viabilit y of ICM cells of frozen-thawed bovine embryos tend to be lower than t hat of unfrozen embryos irrespective of the cryoprotectants used. PG w as significantly more toxic to the ICM cells compared with the other c ryoprotectants. (C) 1994 Academic Press, Inc.