Meeting Abstract

P2.191  Monday, Jan. 5  Urea Loading Enhances Freezing Survival and Postfreeze Recovery in a Terrestrially-Hibernating Frog COSTANZO, J.P.**; LEE, R.E.; Miami Univ., Oxford, OH; Miami Univ., Oxford, OH costanjp@muohio.edu

We tested the hypothesis that urea, an osmolyte accumulated early in hibernation, functions as a cryoprotectant in the freeze-tolerant wood frog, Rana sylvatica. Relative to saline-treated, normouremic (10 mmol l^-1) frogs, individuals rendered hyperuremic (70 mmol l^-1) by administration of an aqueous urea solution exhibited significantly higher survival (100% versus 64%) following freezing at -4^oC, a near-critical temperature. Hyperuremic frogs also had lower plasma levels of intracellular proteins (lactate dehydrogenase, creatine kinase, hemoglobin), which presumably escaped from damaged cells, and more quickly recovered neurobehavioral functions following thawing. Experimental freezing/thawing did not alter tissue urea concentrations, but did elevate glucose levels in the blood and organs of all frogs. When measured 24 h after thawing commenced, glucose concentrations were markedly higher in urea-loaded frogs as compared to saline-treated ones, possibly because elevated urea retarded glucose clearance. Like other low-molecular-mass cryoprotectants, urea colligatively reduces both the amount of ice forming within the body and the osmotic dehydration of cells. In addition, by virtue of certain special properties, it may bestow additional protection from freeze/thaw damage not afforded by glucose. Supported by NSF grant IAB 0416750.