Effects of fat ingestion on high density lipoprotein profiles in human sera

Serum concentrations of triacylglycerol, apolipoprotein A-I, apolipoprotein A-II, HDL2, and HDL3 were determined in sera of nine normolipidemic adult males, just before and 3, 5, and 8 hr after ingestion of 250 ml of cream (100 g of triacylglycerol). In all individuals a rapid hypertriglyceridemic response was observed. Triacylglycerol concentrations increased from 624 +/- 124 mg/liter of serum to 1435 +/- 350 mg/liter of serum 3 hr after cream ingestion. In most individuals the hypertriglyceridemic response was followed by a decline in serum triacylglycerol concentration to below basic levels. As a result of cream ingestion, small but statistically highly significant increases in serum cholesterol and apolipoprotein A-I concentrations were observed that persisted till the end of the observation period. In most individuals a small rise in the apolipoprotein A-II concentration in serum was also present. Marked changes were observed in serum HDL as illustrated in the HDL absorption at 280 nm and cholesterol profiles obtained by single-spin rate-zonal density gradient ultracentrifugation of the sera. Due to a prominent increase in phospholipids (up to about 18%) and a smaller increase in protein (up to about 6%), flotation rates and concentrations of HDL2 as well as HDL3 increased. These changes in HDL subclass flotation characteristics and chemical composition are best explained by uptake of surface material from chylomicrons by existing HDL2 and HDL3 particles. The data do not support a previously proposed concept in which HDL3 is converted into HDL2 by uptake of surface remnants formed during catabolism of triglyceride-rich lipoproteins.