The effects of permeating cryoprotectants on intracellular free-calcium concentrations and developmental potential of in vitro-matured feline oocytes.

Embryos produced from vitrified feline oocytes have resulted in pregnancies, but the efficiency of oocyte vitrification in cats is still low. Our objectives were to evaluate the effects of exposing feline oocytes to ethylene glycol (EG), propanediol (PrOH) and dimethyl sulfoxide (DMSO) on changes in intracellular free-calcium concentrations ([Ca(2+)]i), the time needed for enzymatic digestion of the zona pellucida (ZP), the incidence of parthenogenetic activation and degeneration and embryonic development following in vitro fertilisation (IVF). All of the chemicals tested altered [Ca(2+)]i, but changes in [Ca(2+)]i, resistance of the ZP to enzymatic digestion and the incidence of parthenogenetic activation (<5% for all treatments) were not affected (P>0.05) by extracellular Ca(2+). Exposure to EG (>44.1%) and DMSO (19.7%) increased (P<0.05) oocyte degeneration compared with control oocytes and oocytes exposed to PrOH (≤2.5%). Following exposure to a combination of PrOH and DMSO (10% v/v each), blastocyst development (per cleaved embryo; 52.1%) was similar (P>0.05) to control oocytes (64.4%). When oocytes were vitrified with PrOH and DMSO, 28.3% of surviving (intact plasma membrane) oocytes cleaved following IVF, but no blastocyst developed. When a non-permeating cryoprotectant (galactose, 0.25M) was added to the vitrification medium, 47.7% of surviving oocytes cleaved and 14.3% developed to the blastocyst stage.