Effect of silver iodide as an ice inducer on viability of frozen-thawed rabbit morulae

A new method was devised for inducing ice crystal formation in extracellular solution using silver iodide. A latent heat occurred immediately before temperature of sample reached -7 degrees C, when a column 70 mm high of 1.5M dimethyl sulfoxide (the freezing solution, FS) was aspirated into a plastic straw followed by 3 mm high of air and 10 mm high of 1% suspension of silver iodide in distilled water (1% AgI). To examine the effect of silver iodide as an inducer of ice crystal formation in extracellular solution on in vitro development of frozen-thawed rabbit morulae, the straws were filled by successive aspiration of the following fractions: 175 mul of FS containing the embryos, 7.5 mul of air, 25 mul of 1% AgI. The straws were cooled to -7 degrees C at 1 degrees C/min, and held at -7 degrees C for 10 min without initiating seeding; they were then cooled again to -30 degrees C at 1 degrees C/min and plunged into liquid nitrogen. After rapid thawing (>1000 degrees C/min), 100 of 109 (92%) embryos that were recovered developed into expanding blastocysts.