Studies on plasma lipoproteins during absorption of exogenous lecithin in man

Human subjects were infused intraduodenally with either lecithin (150 mg/kg/hr) or safflower oil (100 mg/kg/hr)of similar fatty acid composition, and plasma lipoproteins were studied when constant plasma lipid levels were reached. Both types of fat induced increases of lipoproteins of Sf > 400 (chylomicrons) and Sf 20--400 (VLDL). Lecithin infusions produced increases predominantly in VLDL, whereas infusion of safflower oil induced mainly chylomicrons. Chylomicrons derived from lecithin were generally smaller and had a high phospholipid:triglyceride ratio (mean 0.15) than those produced during safflower oil infusions (mean 0.08). The increases in VLDL from both lipids occurred mainly in larger particles of this density range. This "incremental VLDL" had a lower cholesterol:triglyceride ratio (0.098) than preinfusion VLDL (0.283) and probably represented "small chylomicrons" of gut origin. The differences in lipoproteins resulting from infusion of lecithin and safflower oil in human subjects were not observed in rats; in the latter, lecithin induced large chylomicrons to the same extent as did safflower oil. Lecithin absorption measured over 50- or 100-cm intestinal segments averaged 41%, but was probably greater over the whole of the small intestine. Lecithin infusion unexpectedly was found to decrease markedly the absorption of cholesterol in the upper part of the small intestine.