Effects of low-density lipoprotein from normal rabbits on hypercholesterolemia and the development of atherosclerosis.

To clarify whether or not normal LDL separated from normal rabbits is atherogenic, 0.75 mg of normal LDL-cholesterol in 6 ml of 0.85% saline and 6 ml of saline alone were injected every day for 5 weeks into the auricular vein of two groups of rabbits, respectively. The inoculated rabbits were fed a standard diet containing 0.5 and 1% cholesterol. Blood was drawn before injection and at 1, 2, 3 and 5 week intervals thereafter. After 5 weeks, all rabbits were sacrificed. Following exsanguination, the aorta was stained by Sudan III. The Sudan III staining was more extensive in rabbits injected with saline than in those that received LDL. In addition, plasma cholesterol, plasma phospholipid, VLDL-cholesterol and LDL-cholesterol levels were lower in LDL-injected rabbits than in those injected with saline. But HDL-cholesterol levels were not significantly different between LDL-cholesterol and saline-injected rabbits. Although the exact cause of antiatherogenic effect of normal LDL is not clear, it seems reasonable to suggest that at least some normal LDL acts as a 'good' lipoprotein, namely antiatherogenic lipoprotein, in our experimental protocol.