Lipid metabolism in arteriosclerotic arterial wall of rats

Arteriosclerotic lesions were formed in rat aorta by the administration of vitamin D2, a high-fat diet and a thyroid suppressing agent. This treatment increased the serum total cholesterol level to 12 times the control level. In the arteriosclerotic lesions that were induced the activities of lysosomal enzymes, such as acid phosphatase and acid lipase, were higher than in controls, that of acid cholesterol esterase was decreased, those of microsomal lipid-synthesizing enzymes--such as acyl-CoA synthetase and cholesterol ester synthesizing activity--were increased and that of neutral cholesterol esterase was decreased. These data suggest that lipid metabolism in arteriosclerotic lesions was changed, resulting in the accumulation of cholesterol esters in the aorta. Administration of high-fat diet and thyroid suppressing agent also increased the serum cholesterol levels to 12-fold the control level, but did not induce arteriosclerotic lesions. After this treatment the activities of hydrolyzing enzymes, such as acid and neutral cholesterol esterase and lipase, in the aorta increased, but the activities of lipid synthesizing enzymes also increased. These data suggest that lipid metabolism in the aorta in this condition changed to compensate for the large influx of serum lipids and to prevent arteriosclerosis. The roles of the serum lipid level, cell injury and lipid metabolism in the aorta in forming arteriosclerotic lesions are discussed on the basis of these results.