Quantitative and qualitative lipid correlation in experimental endogenous hyperlipemia

The reversible endogenous hyperlipemia in dogs, elicited by the detergent Triton which was given intravenously, was used to study the interrelations of serum lipids. In the cholesterol ester fraction an increase occurs in both monounsaturated and in saturated fatty acids, excepting myristic; while a decrease occurs in polyunsaturated fatty acids. The fatty acids of cholesterol esters of normal dogs contain 22% oleic acid, and only 24% when serum lipids are increased to almost double their normal value (TC=400–500 mg/100 ml). However there is a critical level above which a rapid rise in oleic acid occurs and, in severe hyperlipemia (TC=1500 ±430 mg/100 ml), this acid constitutes almost half of the esterified fatty acid component. Since there is no evidence that Triton directly regulates fatty acid synthesis, the lipid fraction-fatty acid interrelationship may be secondary to lipid mobilization from endogenous sources. This concept is supported by the fact that the increased serum fatty acids are only those which can be synthesized by animals. It is suggested, on the basis of a marked increased of endogenously produced fatty acids, that, at critical lipid levels, shortage of polyunsaturated fatty acids from exogenous sources occurs. This might be of sufficient degree to accelerate fatty acid synthesis to meet the need for fatty acids for energy requirements. There may also be need of fatty acid for esterification of chiefly the accumulated free cholesterol split from lipoprotein by Triton. Triton-induced changes in cholesterol ester fatty acids result in patterns which closely resemble those in the adipose tissue of dog and man and in the serum of human endogenous hyperlipemia.