AbstractThe significant seasonal temperature fluctuations in the arid zones of northwestern Dagestan lead to a broad population of heterothermic mammals that have the unique ability to fall into a state of hibernation at low ambient temperatures. Their significant fluctuations in physiological and biochemical processes during and after hibernation indicate that heterotherms have flexible mechanisms to change the functional characteristics of key metabolic enzymes. In this paper, the temperature dependence of the lactate dehydrogenase (LDH) activity in the skeletal muscles of the small ground squirrel Spermophilus pygmaeus Pall. was studied during the period of summer wakefulness, deep hibernation, and at various stages of awakening, accompanied by warming of the animal bodies to temperatures of 10, 20, 30, and 37°C. It was found that the LDH activity substantially decreases in hibernating ground squirrels, regardless of its incubation temperature in vitro. In the dynamics of warming, there is an increase in LDH activity, the progressive nature of which is most pronounced in the range of animal body temperatures of 1.6–20°C. The temperature dependence of LDH activity in Arrhenius coordinates was approximated with nonlinear graphs; their inflection position during hibernation shifted to the low temperature region, returning to the control values after total warming. Hibernation contributed to a significant increase in the energy and enthalpy of LDH activation. In the warming dynamics, the levels of these parameters are disproportionally reduced and reach the control values of summer animals. The results supported the assumption that the mechanisms of LDH catalysis are substantially modified during hibernation and at various stages of awakening in the skeletal muscles of ground squirrels and had an adaptive character.