The effects of time of equilibration with cryoprotectants at 0 degree C prior to freezing on the survival of mouse embryos frozen by the two-step method

Deleterious effect of equilibration temperature on the toxicity of propanediol during cryopreservation of mouse zygotes

PURPOSE

Our aim was to determine the effect of temperature and incubation time on the toxicity of propanediol on mouse zygotes.

METHOD

Zygotes were pooled and randomly allocated to one of the treatment groups. Zygotes were incubated in PBS or PBS containing 1.5M propanediol at 37 degrees C or room temperature (RT) for up to 30 min, washed, and cultured. Similarly, zygotes were incubated at 4 degrees C or RT for 30 min and either washed and cultured or frozen-thawed, washed, and cultured. Zygotes were examined at 24, 48, and 96 hr of culture and embryo quality was determined.

RESULTS

Exposure of zygotes to 1.5 M propanediol at 37 degrees C significantly impaired first cleavage and blastocyst formation compared to exposure at RT (P < 0.0007). Incubation of zygotes for more than 5 min at 37 degrees C significantly reduced embryo development (P < 0.00001). Exposure to propanediol at 4 degrees C results in similar embryo development before and after freeze-thawing compared to exposure at RT.

CONCLUSIONS

Propanediol is toxic to mouse zygotes in a temperature- and time-dependent fashion. Cryopreservation of zygotes after exposure at 4 degrees C appears to be no better than after exposure at RT.