In vivo turnover of different cholesterol esters in rat liver and plasma

Abstract

Turnover rates of different cholesterol esters in rat liver and plasma were determined after injecting fasting rats intravenously with mevalonate-2-C14. Liver and plasma samples were collected at time intervals of 21 min to 24 hr. Gas–liquid chromatography and thin-layer chromatography on silica gel impregnated with silver nitrate were used to determine specific radioactivities of saturated, mono-, di-, and tetra-unsaturated cholesterol esters. The liver samples showed considerable variability from animal to animal, whereas the plasma showed very little individual variability. In liver cholesterol esters, the rate of appearance of total radioactivity in the monounsaturated esters was greater than that in any of the other esters, and the fractional turnover rate of the mono- and diunsaturated esters was greater than that of the saturated esters and arachidonate. These findings are consistent with the results of previous in vitro studies on the hydrolysis and formation of cholesterol esters in liver. All the plasma samples showed a much more rapid fractional turnover of the monounsaturated, compared with the other, esters. The plasma findings can be explained by a more rapid turnover of the very low density lipoprotein cholesterol esters, which contain relatively more cholesteryl oleate, although other explanations are also possible.