Modification of rat plasma lipoproteins induced by acute immobilization stress

To determine the influence of acute stress on plasma lipids and lipoproteins, 66 Wistar rats (31 males and 35 females) were immobilized for 10 hours. Previously, these animals were deprived of food for another 10 hours. Because immobilization involves forced fasting, the control group consisted of 58 rats (30 males and 28 females) that fasted for 20 hours. The immobilized animals showed gastric lesions (94% of the males and 83% of the females). Plasma lipoproteins were separated by ultracentrifugation in the following densities: less than 1.006 g/ml (very low-density lipoproteins (VLDL)), 1.006 to 1.040 g/ml (low-density lipoproteins (LDL)), 1.040 to 1.063 g/ml (high-density lipoproteins fraction 1 (HDL1)), and 1.063 to 1.210 g/ml (HDL2). Measurements were adjusted according to hematocrit value. In male rats, immobilization caused a rise in total plasma cholesterol as a consequence of increases in the VLDL, LDL, and HDL1 fractions. In female rats, however, no significant variations were observed in plasma cholesterol, although there was a slight, but significant, increase in VLDL and LDL cholesterol. Immobilization caused hypertriglyceridemia in both sexes as a result of an increase in triglycerides in all classes of lipoproteins, except in HDL2 in both sexes and VLDL in males. Finally, the protein content of VLDL and LDL increased both in male and female rats; HDL2 levels decreased in female rats. These changes suggest an atherogenic character of stress caused by continuous immobilization during 10 hours.