Incorporation of radioactive phospholipid into subclasses of high-density lipoproteins

The incorporation of orally administered phospholipid into plasma high-density lipoproteins (HDL) was studied in three subjects. Plasma was analyzed by equilibrium density gradient ultracentrifugation, 5, 6, and 8 h after ingestion of 1.1 g [3H-choline, 14C-dilinoleoyl]phosphatidylcholine. At all time points in all subjects, there was a peak of phosphatidylcholine specific activity in fractions of density approximately 1.10-1.13 g/ml, corresponding to the subclass previously designated HDL2a. There was also a more variable, smaller peak of specific activity of phospholipids in HDL2b (1.063-1.100 g/ml) and in fractions of density approximately 1.19 g/ml. In the 1.10-1.13 fraction, 97 and 71%, respectively, of the 3H and 14C radioactivity were in phospholipids. The 3H/14C ratio was similar in phospholipids of HDL subfractions, the d less than 1.07 fraction, and in the administered phospholipid. The results show preferential transfer or exchange or absorbed phosphatidylcholine into specific subclasses of HDL.