ABSTRACT
The development of successful methods for cryopreservation of oocytes and embryos must ensure that cells are not damaged by chilling, the formation of extracellular and intracellular ice, the chemical toxicity of cryoprotectants, fracturing, and osmotic swelling and shrinkage. Two main methods are currently employed for cryopreservation of oocytes and embryos: slow cooling rate with low concentration of cryoprotectants, and fast cooling after incubation in highly concentrated cryoprotectant solutions (vitrifi cation) (1,2). In both techniques, however, one of the main challenges is to rapidly replace intracellular water with cryoprotectant. Vitrifi - cation protocols on specifi c developmental stages of oocytes or embryos result in acceptable survival rates (3,4), but identical protocols often fail when they are applied to other stages of the same species (5). These observations suggest that the cryobiological properties of oocytes and embryos may change during development. Investigation of the mechanisms regulating water and solute permeability in oocytes and embryos, for which current knowledge is still scarce, is essential to improve current cryopreservation protocols.
