Quick freezing of rat embryos

Quick freezing of rat morulae and blastocysts was attempted after they were dehydrated at room temperature. Combined solutions of 2.8 M glycerol and 0.125, 0.25, 0.50 and 1.0 M sucrose in phosphate buffered saline + 20% steer serum were compared. Survival rates (expanding blastocysts 15 h after thawing) were 42.1, 79.4, 87.5 and 16.7%, respectively (P<0.01). Freezing procedures consisted of either a direct plunge into liquid nitrogen (48.8%), holding for 5 min in the neck of a liquid nitrogen container or holding the samples for 60 min at -30 degrees C before insertion into liquid nitrogen. The direct plunge method resulted in a lower survival rate than either the 5- or the 60-min treatments (48.8% vs 76.9% and 77.6%, respectively). After thawing, dilution at room temperature in sucrose solutions of 0.25, 0.50 and 1.0 M gave survival rates of 80.0, 90.6 and 69.4%, respectively (NS). If diluted directly in PBS + 20% steer serum, 86.8% of embryos survived at +37 degrees C vs 0% at 0 degrees C (P<0.01).