Cryoprotectant Production Capacity of the Freeze-Tolerant Wood Frog, Rana Sylvatica
71 Cryoprotectant production capacity of the freeze-tolerant wood frog, Rana sylvatica JoN P. Cosr,cNzo AND Rlcnano E. LsE, Jn. Department of Zoology, Miami University, Oxford, OH 45056, U.S.A. ReceivedJune 8. 1992 AcceptedAugust 17, 1992 CosmNzo, J. P., and LBp, R. E., Jn. 1993. Cryoprotectantproduction capacityof the freeze-tolerantwood frog, Rana sylvatica.Can. J. Zool. 7I: 7l-75. Freezingsurvival of the wood frog (Rana sylvatica)is enhancedby the synthesisof the cryoprotectantglucose, via liver glycogenolysis.Because the quantityof glucosemobilized during freezingbears significantly on the limit of freezetolerance, we investigated the relationship between the quantity of liver glycogen and the capacity for cryoprotectant synthesis. We successfullyaugmented natural levels of liver glycogenby injecting cold-conditionedwood frogs with glucose.Groups of 8 frogs having mean liver glycogenconcentrations of 554 + 57 (SE), 940 + 57, and 1264 + 66 pmollg catabolized98.7, 83.4, and 52.8%, respectively,of their glycogenreserves during 24 h of freezingto -2.5'C. Glucoseconcentrations con- comitantly increased,reaching 2l + 3, 102 + 23, and 119 + 14 pmollg, respectively,in the liver, and 15 * 3,42 + 5, and 6l * 5 pcmol/ml-, respectively, in the blood. Becausethe capacity for cryoprotectant synthesisdepends on the amount of liver glycogen,the greatestrisk of freezinginjury likely occursduring spring,when glycogenreserves are minimal. Non- glucoseosmolites were important in the wood frog's cryoprotectantsystem, especially in frogs having low glycogenlevels. Presumably the natural variation in cryoprotectant synthesis capacity among individuals and populations of R. sylvatica chiefly reflectsdifferences in glycogenreserves; however, environmental,physiological, and geneticfactors likely are also involved. CosmNzo, J. P., et LEs, R. E., Jn.
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