Myoglobin content in skeletal muscles of hibernating ground squirrels rises in autumn and winter

The content of myoglobin (Mb) in skeletal muscles of Arctic Yakutian ground squirrel (Citellus undulatus Pallas) was measured in the active euthermic summer and prehibernating autumn animals as well as in hibernating and awak e animals in winter. The myoglobin content in winter, irrespective of the s tate of the animal, was found to be about three times higher than in summer . The content of myoglobin in autumn was also two-fold increased compared t o summer, suggesting that high myoglobin level is necessary for hibernation . Analysis of biochemical data available suggests that the increase in myog lobin content in winter is probably related to a high oxygen demand of musc les at the first stage of arousal (non-shivering thermogenesis) when rectal temperature rises from 0 to 10-12 degrees C, At this stage, the oxygen-dep endent processes in muscles proceed under the conditions when peripheral bl ood flow is blocked and anaerobic glycolysis is switched off. (C) 1999 Else vier Science Inc. All rights reserved.