Changes in plasma very low density and low density lipoprotein content, composition, and size after a fatty meal in normo- and hypertriglyceridemic man.

Four subfractions of plasma VLDL characterized by decreasing Sf value and LDL were isolated by density gradient preparative ultracentrifugation from normotriglyceridemic (NTG) and hypertriglyceridemic (HTG) (type IV) subjects in the fasting state and after a fatty meal. Chemical analysis and computation of numbers of particles in each fraction showed that the hyperlipidemia of type IV subjects was accounted for by an increase in total numbers of VLDL and a shift in the distribution of VLDL towards particles of larger diameter. Postprandial hyperlipidemia was due to the presence of chylomicron remnants rather than intact chylomicrons, and was accounted for by an increase in particle diameter of the largest VLDL subfraction rather than by an increase in particle numbers. Postprandial hyperlipedemia was accompanied by a shift in the distribution of VLDL towards particles of larger diameter in both NTG and HTG subjects, probably because of competition for the triglyceride-depletion process between chylomicrons and hepatic VLDL. Most chylomicron remnants were removed from the circulation without degradation to smaller VLDL or to LDL, but some remnants were sufficienty small to contribute to smaller VLDL subfractions. The LDL of type IV subjects contained more apoprotein B than those from NTG subjects, and this difference was associated with increases in diameter, molecular weight, density, and the ratio of protein: phospholipid in LDL from type IV subjects. Defective degradation of large VLDL to small VLDL, and of VLDL to LDL may be related to this alteration in apoprotein B content of the lipoproteins in type IV subjects.