Abstract
To examine the sensitivity of mammalian oocytes and embryos to osmotic shrinkage, which can occur during the process of removal of cryoprotectant from cryopreserved cells, the effect of shrinkage on the survival of fresh and vitrified mouse oocytes at metaphase II and embryos at 1-cell to blastocyst was examined. Oocytes and embryos were suspended in PBS media containing various concentrations of sucrose for 30 min at 25°C. They were then returned to isotonic PBS, and the survival was assessed in vitro. Fresh oocytes and embryos were almost entirely insensitive to shrinkage in a solution with 0.75 M sucrose, but in solutions with 1.0-1.5 M sucrose, oocytes and 8-cell embryos were more sensitive to the hypertonic stresses, whereas 2-cell embryos and expanded blastocysts were less sensitive. Vitrified embryos were more sensitive to hypertonic stresses than were fresh ones, but the sensitivity was reduced when the embryos had been cultured for a short period before subjecting them to the hypertonic stress.
