Seasonal changes in mechanical resistance of erythrocytes of the long-tailed ground squirrel (Citellus undulatus)

Seasonal changes of relative blood reticulocytes counts in free plasma hemoglobin and mechanic erythrocyte resistance were studied in the long-tailed ground squirrel (Citellus undulatus) under different functional conditions (winter hibernation, forced arousal in winter and summer activity). A significant increase in reticulocytes counts in the ground squirrel blood was observed in April and October, indicating the enhancement of erythropoeisis. This conclusion is also confirmed by a significant increase in free plasma hemoglobin at these periods. It has been also shown that erythrocytes of hibernating animals and forcibly awaken winter ground squirrels have a significantly lower mechanical resistance in comparison with those of active summer animals. The data obtained indicate that during the periods preceding the onset of winter hibernation and transition to summer activity there occurs a seasonal replacement of the erythrocyte pool by a pool more adapted to performance in the novel functional state of the animal-hibernator.