Volumetric behaviour and survival of mouse zygotes and embryos in hyperosmotic media

Volume changes and survival of mouse zygotes and pre-implantation embryos were studied after their exposure to hyperosmotic media. Transfer of zygotes from culture medium to medium containing 1.5 M DMSO led to a rapid volume reduction to 60% of control values. After 10 min the volume was normal again, illustrating the rapid penetration of DMSO at room temperature. Re-transfer of zygotes equilibrated in 1.5 M DMSO to culture medium in one step doubled the volume. Twelve minutes later normal diameters were observed again. Volume changes were also recorded after transfer to media rendered hypertonic by the addition of NaCl or sucrose. A proportional decrease in volume was noticed up to 1500 mOsmol. A further increase in measured osmolarity up to 3100 mOsmol led only to limited further shrinkage of the zygotes (minimal volume observed was 27% of control volume). Addition of 1.5 M DMSO or 1.5 M propanediol had no influence on the final volume reaction to NaCl and sucrose. Exposure to media with a measured osmotic value of 3200 mOsmol (NaCl added) during 10 min did not prevent further development of the embryos to the hatched blastocyst stage. A solution of 4000 mOsmol proved lethal to nearly all embryos. Addition of 1.5 M DMSO to this medium did not have a protective effect against the osmotic stress at room temperature.