No abstract

The annual cycle of small ground squirrels (Spermophilus pygmaeus) consists of 2 periods: wakefulness (spring−autumn) and hibernation (winter). During the active period, ground squirrels breed (spring), accumulate fat reserves (summer) and prepare for hibernation (autumn). We suppose that the rheological properties of blood and the deformability of erythrocytes can change in different seasons of the animal's wakefulness period to adequately provide tissues with oxygen. The aim of this study was to identify possible adaptive changes in erythrocyte deformability and erythrocyte indices in ground squirrels during their active period. The deformability of erythrocytes was studied by ektacytometry in an osmotic gradient. It was found that in spring, after the arousal of ground squirrels, erythrocytes have the highest deformability (El_max), hydration (O_hyper), water permeability (El_min) and osmotic stability (∆O). In summer, compared with spring, the deformability of erythrocytes decreases, and the average volume of erythrocytes (MCV) also decreases. In autumn, before hibernation, the integral deformability of erythrocytes, their hydration, as well as the range of osmotic stability of erythrocytes increases relative to the summer period. In summer and autumn, in contrast to spring, the average concentration of hemoglobin in the erythrocyte (MCHC) increases. At low shear stress (1 Pa) in summer and autumn, osmoscan becomes a pronounced polymodal form, indicating a change in the viscoelastic properties of ground squirrel erythrocyte membranes. Thus, for the first time, we discovered seasonal variability in the deformability of ground squirrel erythrocytes, which is consistent with the spring‐summer activity of animals and preparation for hibernation.

The hibernation of small mammals is characterized by long torpor bouts alternating with short periods of arousal. During arousal, due to a significant increase in oxygen consumption, tissue perfusion, and the launch of thermogenesis in cells, a large amount of reactive oxygen species (ROS) and nitrogen (RNS) can be formed, which can trigger oxidative stress in cells. To estimate this possibility, we studied the intensity of free-radical processes in the red blood cells (RBCs) of little ground squirrels (LGS; Spermophilus pygmaeus) in the dynamics of arousal from hibernation. We found that in the torpid state, the degree of generation of ROS and RNS (8.3%, p>0.09; 20.7%, p<0.001, respectively), the degree of oxidative modification of membrane lipids and RBC proteins is at a low level (47%, p<0.001; 82.7%, p<0.001, respectively) compared to the summer control. At the same time, the activity of superoxide dismutase (SOD) and catalase (CAT) in RBC is significantly reduced (32.8%, p<0.001; 22.2%, p<0.001, respectively), but not the level of glutathione (GSH). In the torpid state, SOD is activated by exogenous GSH in concentration-dependent manner, which indicates reversible enzyme inhibition. During the arousal of ground squirrels, when the body temperature reaches 25°C, RBCs are exposed oxidative stress. This is confirmed by the maximum increase in the level of uric acid (25.4%, p<0.001) in plasma, a marker of oxidative modification of lipids [thiobarbituric acid reactive substances (TBARS); 82%, p < 0.001] and proteins (carbonyl groups; 499%, p < 0.001) in RBC membranes, as well as the decrease in the level of GSH (19.7%, p < 0.001) in erythrocytes relative to the torpid state and activity of SOD and CAT in erythrocytes to values at the Tb 20°C. After full recovery of body temperature, the level of GSH increases, the ratio of SOD/CAT is restored, which significantly reduces the degree of oxidative damage of lipids and proteins of RBC membranes. Thus, the oxidative stress detected at Tb 25°C was transient and physiologically regulated.