Seasonal changes in myoglobin content in muscles of hibernating Yakutian ground squirrels

Myoglobin content in skeletal muscles of the Yakutian ground squirrel Citellus undulatus was measured during different periods of the annual life cycle: in active animals in summer, and in hibernating and awake animals in winter. It was found that the Mb content in winter, irrespective of the state of the animal (hibernating or awake), is 2.5-3-fold higher than in summer. Analysis of biochemical data available in the literature suggests that the increase in Mb content in winter is most probably related to a high oxygen demand of muscles at the first stage of arousal when the body temperature rises from 0 to 10-12 degrees C (non-shivering thermogenesis or thermoregulatory tonus). At this stage, the oxygen-dependent processes in muscles proceed under conditions of blocked peripheral blood flow and failure of anaerobic glycolysis.