Synthesis of Serum and Sub-cellular Liver Cholesterol Esters in Fasted and Fed Rats

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Abstract
The formation of serum and liver sub-cellular liver cholesterol esters was investigated in fasting and fed rats. Rats were injected with cholesterol-4-14C-labeled serum and the liver and serum cholesterol esters examined at 45, 90, and 180 minutes. There was a marked heterogeneity in the labeling of the cholesterol esters in the liver cell fractions and serum. In both fasting and fed rats the soluble fraction 14C-esters had a higher proportion of 14C-arachidonate than the particulate liver fractions. Fasting rats had a higher percentage of 14C-arachidonate in the liver cell fractions and serum cholesterol esters than fed rats. There were also comparable differences in the cholesterol ester fatty acid composition. The differences in 14C-activity distribution and cholesterol ester fatty acid composition were principally at the expense of monounsaturated esters. The specific activity of the liver cell fraction esters exceeded the specific activity of the corresponding esters in the serum. Cholesterol arachidonate in serum and liver had the highest fractional turnover rate. The data suggest that there is a compartmentalization of cholesterol ester metabolism in the liver and that the liver is the major source of the serum esters. The types of cholesterol esters synthesized in the liver and released into the blood are dependent on the nutritional status of the animal.