Freeze duration influences postfreeze survival in the frog Rana sylvatica

Survival, cryoprotection, and the time course for recovery of vital functions were studied in autumn-collected juvenile wood frogs (Rana sylvatica) following freezing at -1.5 degrees C for various periods. Frogs readily tolerated freezing for 3 or 9 d, but only 50% survived a 28-d freezing trial. Generally, the postfreeze return of vital functions (vascular circulation, pulmonary breathing, righting reflex, jumping reflex) occurred later in frogs frozen for longer periods. Augmenting endogenous levels of the cryoprotectant glucose (via injections) prior to freezing substantially increased freeze endurance, as these frogs had excellent survival after remaining frozen for as long as 49 d. The improved freeze endurance of glucose-loaded frogs apparently was not associated with a reduction in ice content but rather may reflect the greater availability of energy substrate needed to support metabolism of frozen ischemic tissues.