Blood Plasma Phospholipids and Cholesterol during Hibernation of the Long-Tailed Ground Squirrel

Seasonal changes in the levels of phospholipids, diglycerides, cholesterol, and total protein in the blood plasma were investigated during hibernation of the long-tailed ground squirrel Spermophilus undulatus. During the winter period, the levels of phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, lysophosphatidylcholine, and sphingomyelin phospholipids (per 1 mg of plasma protein) were increased in both torpid and active ground squirrels by 70–80, 50, 600–700, 70, and 150–200%, respectively; the level of phosphatidylserine did not change in comparison to the summer period. The plasma phospholipid composition differed between hibernating and active summer animals: in winter, the phosphatidylcholine mol % decreased by 20%, phosphatidylinositol and phosphatidylethanolamine increased by 3–4 times, and the phosphatidylserine mol % decreased by 50%, while sphingomyelin and lysophosphatidylcholine did not change in comparison to summer animals. In hibernating ground squirrels, the plasma cholesterol levels increased by two times, the diglyceride content diminished by 60%, and the level of protein (in milligrams per 1 mL plasma) increased by 20%. The simultaneous increase in the levels of cholesterol and total phospholipids, as well as the pronounced specific changes in the levels of individual phospholipids in the blood plasma of hibernating ground squirrels, indicate the involvement of plasma lipoprotein lipids in the molecular mechanisms of adaptation to natural hypobiosis in mammals and a possible role of these mechanisms in systemic reactions to damaging factors.