The major objective of this research project is to examine the effects of exercise training on kinetic parameters of apolipoprotein B (apoB) metabolism in elderly adults. Elevated levels of plasma low density lipoprotein cholesterol (LDL-C) and apoB have been associated with an increased risk of coronary heart disease and myocardial infarction. In addition, there is an age related increase in plasma LDL-C and apoB concentrations. As such, the increased risk for cardiovascular events in the elderly may be explained at least in part, by the age related effect on apoB metabolism. ApoB levels in plasma are a function of the rate at which they are produced as well as the rate at which they are catabolized. Nevertheless, the changes in apoB metabolism occurring with aging have not been well characterized. Exercise training has been shown to decrease LDL-C and apoB plasma concentration in healthy adults. The underlying mechanism, however, for the exercise-induced salutary changes in apoB concentration remains unclear. Specifically, the purpose of this project is to clarify whether exercise training decreases production and/or increases catabolism of apoB containing lipoproteins, thus enhancing cardiovascular risk profile in elderly adults. Before and after sixteen weeks of exercise training, total cholesterol, triglyceride, plasma lipoprotein (VLDL, IDL, LDL) and apolipoprotein b levels will be determined. The synthesis rate of apoB will be determined before and after exercise training by measuring the incorporation rate of intravenously infused [1-13C] leucine into the apoB fraction of VLDL, IDL and LDL isolated from plasma. Plasma and apoB [1-13C] leucine enrichment will be determined by gas chromatography mass spectrometry, and used to solve the multi compartmental model of apoB metabolism previously developed by the associate investigators. The results of this protocol will characterize how exercise training regulated the synthetic rate of apoB containing lipoproteins and will add to understanding of cholesterol metabolism in the elderly.
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