Cholesterol ester fatty acids in serum and liver of normal and lymph-fistula rats.

Data on the normal distribution of fatty acids in the cholesterol ester fraction of rat plasma and liver and on factors which may influence their distribution are extremely limited at the present time. The information available has been obtained by alkali isomerization and silicic acid and paper chromatography techniques. These methods do not provide an adequate identification and estimation of the individual fatty acid components. Mukherjee et al. (1) reported that in normal rat blood, although the cholesterol ester fraction had a higher iodine value than the other lipid fractions, saturated fatty acids made up 56% of the cholesterol ester fatty acids and that oleic acid was absent. Contrary to these findings, Klein and Janssen (2) reported that oleic acid constituted up to 59% of the cholesterol ester fatty acids of rat plasma. Studies (3-5) on the composition of the liver cholesterol ester fatty acids are in general agreement that this tissue contains a large proportion of saturated fatty acids and that these cholesterol esters differ markedly in composition from plasma cholesterol esters (3). In an earlier study from our laboratories (6) with the aid of gas-liquid chroma.tography, it was shown that human serum and liver were also markedly different in their cholesterol ester fatty acid composition. The principal fatty acids of liver esters were found to be oleic and palmitic, whereas in the serum the polyunsaturated fatty acids constituted up to 52 %, with linoleic acid the major fatty acid. These findings were in agreement with earlier studies (7, 8) which suggested that under normal conditions a large portion of the plasma cholesterol esters in the rat and man arise from extrahepatic sources. The present study was undertaken to provide quantitative data on the cholesterol ester fatty acid composition of normal rat serum and liver and to determine what effect the diversion of lymph cholesterol would have on the cholesterol ester fatty acid spectrum. Silicic acid chromatography followed by gas-liquid chromatography were used to separate and quantitate individual fatty acid components.