MODIFICATION OF RAT PLASMA-LIPOPROTEINS INDUCED BY ACUTE IMMOBILIZATION STRESS

To determine the influence of acute stress on plasma lipids and lipopr oteins, 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 2 0 hours. The immobilized animals showed gastric lesions (94% of the ma les and 83% of the females). Plasma lipoproteins were separated by ult racentrifugation in the following densities: less than 1.006 g/ml (Ver y low-density lipoproteins (VLDL)), 1.006 to 1.040 g/ml (low-density l ipoproteins (LDL)), 1.040 to 1.063 g/ml (high-density lipoproteins fra ction 1 (HDL(1))), and 1.063 to 1.210 g/ml (HDL(2)). Measurements were adjusted according to hematocrit value. In male rats, immobilization caused a rise in total plasma cholesterol as a consequence of increase s in the VLDL, LDL, and HDL(1) fractions. In female rats, however, no significant variations were observed in plasma cholesterol, although t here was a slight, but significant, increase in VLDL and LDL cholester ol. Immobilization caused hypertriglyceridemia in both sexes as a resu lt of an increase in triglycerides in all classes of lipoproteins, exc ept in HDL(2) in both sexes and VLDL in males. Finally, the protein co ntent of VLDL and LDL increased both in male and female rats; HDL(2) l evels decreased in female rats. These changes suggest an atherogenic c haracter of stress caused by continuous immobilization during 10 hours .