FREEZE DURATION INFLUENCES POSTFREEZE SURVIVAL IN THE FROG RANA-SYLVATICA

Survival, cryoprotection, and the time course for recovery of vital fu nctions were studied in autumn-collected juvenile wood frogs (Rana syl vatica) following freezing at -1.5 degrees C for various periods. Frog s 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 r eflex) occurred later in frogs frozen for longer periods. Augmenting e ndogenous levels of the cryoprotectant glucose (via injections) prior to freezing substantially increased freeze endurance, as these frogs h ad excellent survival after remaining frozen for as long as 49 d. The improved freeze endurance of glucose-loaded frogs apparently was not a ssociated with a reduction in ice content but rather may reflect the g reater availability of energy substrate needed to support metabolism o f frozen ischemic tissues. (C) 1998 Wiley-Liss,Inc.