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Accumulation of Lactate by Frozen Painted Turtles (Chrysemys picta) and Its Relationship to Freeze Tolerance
Mary J. Packard and Gary C. Packard
Physiological and Biochemical Zoology: Ecological and Evolutionary Approaches
Vol. 77, No. 3 (May/June 2004), pp. 433-439
Published by: The University of Chicago Press. Sponsored by the Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology
Stable URL: http://www.jstor.org/stable/10.1086/420952
Page Count: 7
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Abstract Hatchling painted turtles (Chrysemys picta) survived freezing at −2°C for 4 d, few recovered from freezing lasting 6 d, and none survived being frozen for 8 d. Whole‐body glucose and lactate were low in animals that had not been subjected to cold and ice but increased precipitously in animals that were frozen for 2 d. Both metabolites continued to increase, but at a somewhat lower rate, in animals frozen for 4, 6, or 8 d. The increase in whole‐body lactate reflects a reliance by frozen hatchlings on anaerobiosis, whereas the increase in glucose presumably results from mobilization of glycogen reserves to support anaerobic metabolism. Mortality of frozen hatchlings is correlated with the increase in whole‐body lactate. Factors that may contribute to the observed correlation include a compromised capacity for individual organs to cope with the lactic acidosis that accompanies anaerobic metabolism and organ‐specific depletion of energy reserves. Individual organs must rely on buffering and glucose reserves available in situ because blood of frozen hatchlings does not circulate. Thus, buffer from the shell cannot be transported to other organs, lactate cannot be sequestered in the shell, and glucose mobilized from liver glycogen is not available to supplement glucose reserves of other tissues. This integrated suite of physiological disruptions may limit tolerance of freezing to conditions with little or no ecological relevance.
© 2004 by The University of Chicago. All rights reserved.