The relationship between the linoleic acid content of the diet, the fatty acid composition of the plasma phospholipids and the degree of aortic atherosis in experimental rabbits

Abstract

Groups of male rabbits (10 to 13/group) were given ad lib a diet consisting of 80 parts of a low-fat basal ration which were added for group 1,20 parts maize oil; for group 2,20 parts butterfat; for group 3, 10 parts maize oil and 10 parts butterfat; for group 4, 0.47 parts maize oil and 43 parts wheat starch; and for group 5, 102 parts maize oil and 21.6 parts wheat starch. The animals in group 6 were given an ordinary commercial diet. After the animals were given the various diets for a period of 38 weeks a large sample of blood was taken from each animal. The animals were then killed and the degree of atheromatous degeneration was determined after the aortas were stained with Sudan IV. The fatty acid composition of the plasma phospholipids was determined by gas-liquid chroma tog raphy. In all the groups, the major fatty acids present in the plasma phospholipids were stearic, palmitic, oleic and linoleic. Although linoleic acid tended to replace oleic acid in the plasma phospholipids when the rabbits were given high levels of linoleic acid in the diet, there appeared to be a limit to the extent to which the concentration of linoleic acid in the plasma phospholipids increased. There were highly significant inverse relationships between the concentrations of oleic and linoleic acids and between the concentrations of palmitic and stearic acids in the plasma phospholipids. There were significant positive correlations between the concentrations of palmitic and oleic acids and between the concentrations of stearic and linoleic acids. Since lecithin was the major component of the plasma phospholipids these correlations suggest that when the [beta]-position of lecithin is occupied by oleic acid the [alpha]-position tends to be occupied by palmitic acid and that when the [beta]-position is occupied by linoleic acid the [alpha]-position tends to be occupied by stearic acid. In the plasma phospholipids of the 2 groups of rabbits with extensive atheromatous degeneration of the aorta, the linoleic: oleic acid ratio in the plasma phospholipids was considerably greater than the corresponding ratio observed for the plasma phospholipids of the remaining 4 groups of rabbits in which little or no aortic atherosis occurred. The relationships between the level of linoleic acid in the diet the level of phospholipid and the phospholipid: cholesterol ratio in the plasma and the extent of atheromatous degeneration of the aorta are discussed. It is suggested that, under certain circumstances, the level of linoleic acid in the diet may limit the rate of phospholipid synthesis in the liver and hence the level of phospholipid circulating in the plasma.