The Dynamics of Adaptive Changes in the Spleen of the Hibernating Ground Squirrel <Emphasis Type="Italic">Spermophilus undulatus</Emphasis>

In hibernation season during torpor bouts, the spleen weight and the hemoglobin level, as well as the total and extracted protein contents in the spleen of the ground squirrel Spermophilus undulatus are increased when animals enter torpor and reach maximum values when the body temperature drops below 25°C. All these parameters return to the characteristic values of the euthermic animals during arousal, before the body temperature increases to 20°C. There were no significant differences in the numbers of splenocytes between ground squirrels in interbout euthermia and torpor. The minimum number of splenocytes was observed in animals that entered torpor when the core body temperature was approximately 18°C. The activity of ornithine decarboxylase, a key enzyme in polyamine synthesis, which is correlated with the functional and proliferative status of lymphoid tissue, was the same for the euthermic and summer ground squirrels and decreased monotonically during torpor. Upon arousal of the animals when body temperature was below 29°C, no resumption of the spleen ornithine decarboxylase activity was observed.