The objective of this study is to describe the regulation by dietary lipid of rat aorta membrane structure and function. Lipids are a major structural component of membranes and dietary manipulation is a physiologically relevant method of altering membrane lipid composition. Rats will be fed diets containing cholesterol with either lard or safflower oil or a fat-free diet. Appropriate control diets without cholesterol will also be fed. Lipid metabolic enzymes, membrane microviscosity and membrane lipid composition will be assayed in the aorta and these measurements will be correlated with similar data from liver membrane preparations. Plasma lipoproteins may play a significant role in the control of aorta properties and reflect the status of lipid metabolism in the organism. Therefore plasma lipoproteins will be isolated from these rats and lipid and protein composition analyzed. The significance of the diet of the rat in determining aorta and liver membrane properties and in regulating lipid metabollsm will be established. Dietary intervention is recommended therapy for prevention of atherosclerosis but the biochemical basis for this recommendation is not established. These studies will give us an understanding of the significance of the fatty acid composition and cholesterol content of the diet in regulating membrane properties of the aorta and will give us an insight into the metabolic basis for this regulation.