The Influence of Some Dietary Factors and/or Treadmill Exercise on Rat and Chicken Tissue Lipids and Serum Lipoproteins

Abstract

Four different experiments, one with cockerels and three with rats, are described which relate to the effect of dietary factors and/or exercise on serum and liver lipids as well as on serum lipoproteins. Several classes of lipoproteins were isolated by preparative ultracentrifugation, and their purity assessed by gel electrophoresis. The lipid composition and protein content of serum lipoproteins and tissue were also determined. Dietary cholesterol produced an enormous increase (200 fold) in serum very low density lipoproteins in cockerels. This lipoprotein was apparently of very large particle size because it failed to penetrate the spacer gel during disc electrophoresis. In rats fed a cholesterol-supplemented diet, the increase in very low and low density lipoproteins was relatively insignificant in comparison with the cockerels. However, in both species, the liver was overloaded with cholesterol. Further, the serum high density lipoproteins, HDL2 were greatly diminished in both species as a result of cholesterol ingestion for 7 weeks. As a possible explanation for these related observations, it was proposed that HDL2 was utilized in the formation of cellular membranes by cholesterol-burdened, hyperplastic livers. A very high level of dietary corn oil (40% by weight) caused drastic changes in rat liver lipid levels and in serum lipoprotein profiles. Specifically, liver cholesterol and triglycerides were increased about 200% over normal. In another experiment, tissue lipids and serum lipoprotein levels were determined in treadmill-exercised rats and in sedentary controls. Two levels (4 and 40%) of a fat mixture (1:1, hydrogenated coconut oil: corn oil) were used in this study. The serum cholesterol was unchanged in the 4 groups, while the serum triglycerides were reduced in exercised rats given 4% but not 40% fat as compared to respective controls. Rats fed 40% fat and exercised had near normal levels of liver lipids which was in sharp contrast to their sedentary controls. The low denstiy lipoproteins were surprisingly higher in exercised rats given high fat than in sedentary controls. It was suggested that the direct synthesis of these lipoproteins by the liver may be necessitated under unusual conditions. In conclusion, considering the central role of liver in lipid and lipoprotein metabolism greater attention should be focused on this organ in future experiments on the control of hyperlipoproteinemia.