Fatty acid specificities and rates of cholesterol esterification in vivo and in vitro

Abstract

The esterification of cholesterol and the formation of different fatty acid esters of cholesterol were studied after the administration of radiomevalonate or cholesterol-4-C 14 to rats or Cebus monkeys. Cholesterol-4-C 14 in the free form for intravenous injection was prepared by incubation of plasma at 0 ° C with radiocholesterol on Celite. After injection of mevalonate-2-C 14 into rats or monkeys or cholesterol-4-C 14 into rats, the specific activity of plasma cholesteryl arachidonate was higher and that of cholesteryl oleate lower than the specific activity of total plasma cholesterol esters for at least 6 hours. After the administration of cholesterol-4-C 14 intravenously, the free cholesterol specific activity of liver was equal to that of plasma within 1 hour, but the ester cholesterol specific activity of plasma was three times greater than that of liver at 1 hour. The liver and plasma cholesterol ester specific activities did not become equal for nearly 12 hours. Cholesterol-4-C 14 esterification by plasma in vitro resulted in a heterogeneous pattern similar to that seen in the early periods of the in vivo experiments. Esterification of radiocholesterol with different fatty acids by liver preparations in vitro was not similar to that seen in plasma. It was concluded from estimates of the rates of cholesterol esterification in plasma in vivo and in vitro that the plasma esterification activity was of considerable significance in maintenance of the level of plasma cholesterol esters. It was proposed that the early heterogeneity of labeling of different cholesterol esters in vivo resulted from the initial preponderant effect of the plasma esterification activity.