Cholesterol turnover in swine plasma lipoproteins.

The kinetics of free and esterified cholesterol labeling were studied in the plasma lipoproteins of three groups of six adult Large White sows, after either an intravenous injection of autologous red cells previously labeled with [3H]-cholesterol, an intravenous injection of [14C]-acetate, or a [14C]-cholesterol labeled meal. The specific radioactivities became equal in plasma and red cell cholesterol about 96 hours after each pulse of radioactive cholesterol. This finding indicates that red cell cholesterol is completely exchangeable in vivo, with a turnover time of 8.5 hours. The VLDL were shown to play a preferential role in the transport in the plasma of newly synthetized cholesterol. This role is shared with chylomicrons in the transport of absorbed dietary cholesterol, which appears in the plasma mainly as esterified cholesterol. Cholesteryl esters of VLDL are not the main source for those of LDL, which could be labeled by intraplasmatic exchanges or transfers of esterified cholesterol.