Effect of 1,2-propanediol versus 1,2-ethanediol on subsequent oocyte maturation, spindle integrity, fertilization, and embryo development in vitro in the domestic cat

This study assessed the impact of various cryoprotectant (CPA) exposures on nuclear and cytoplasmic maturation in the immature cat oocyte as a prerequisite to formulating a successful cryopreservation protocol. In experiment 1, immature oocytes were exposed to 0, 0.75, 1.5, or 3.0 M of 1,2-propanediol (PrOH) or 1,2-ethanediol (EG) at room temperature (25degreesC) or 0degreesC for 30 min. After CPA removal and in vitro maturation, percentage of oocytes reaching metaphase II (MII) was reduced after exposure to 3.0 M PrOH at 0degreesC or 3.0 M EG at both temperatures. All CPA exposures increased MII spindle abnormalities compared to control, except 1.5 M PrOH at 25degreesC. In experiments 2 and 3, immature oocytes were exposed to CPA conditions yielding optimal nuclear maturation that either had caused spindle damage (0.75 M PrOH, 1.5 M EG, and 3.0 M PrOH at 25degreesC) or not (1.5 M PrOH at 25degreesC). After maturation and insemination in vitro, oocytes were cultured for 7 days to assess treatment influence on developmental competence. CPA exposure did not affect fertilization, but the high incidence of MII spindle abnormalities resulted in a low percentage of cleaved embryos. Blastocyst formation and quality were influenced by both CPA types (EG was more detrimental than PrOH) and concentration (3.0 M was more detrimental than 1.5 M). Overall, cat oocytes appear to be highly sensitive to CPA except after exposure to 1.5 M PrOH at 25degreesC, a treatment that still allowed similar to60% of the oocytes to reach MII and similar to20% to form blastocysts.