Replacement of endogenous phospholipids in rat plasma lipoproteins during intravenous infusion of an artificial lipid emulsion

Male Wistar rats, weighing 250–300 g, were intravenously infused (0.33 ml/h per 100 g body weight) with an artificial emulsion of soybean triacylglycerols and egg yolk phospholipids (Intralipid) for various periods of time ranging from a few hours to a few days. About 0.5 h after the infusion, the animals were sacrificed, various classes of plasma lipoproteins were isolated by centrifugation, and the total lipid profiles of the fractions were determined by high temperature gas chromatography. The lipoproteins collected after 24 h of infusion were subjected to a complete analysis of the molecular species of the various lipid classes. It was shown that continuous intravenous infusion of Intralipid, despite rapid apparent clearance of the visible lipid particles, resulted in a gradual accumulation of exogenous phosphatidylcholine and sphingomyelin, free cholesterol, and plant sterols in the plasma, which displaced the endogenous phospholipids and sterols from the various lipoproteins. At 24 h, about 70% of the endogenous phospholipid of all the plasma lipoproteins was replaced by egg yolk phospholipids of the Intralipid. Under the same conditions, no displacement nor exchange was observed of endogenous cholesteryl esters for exogenous triacylglycerols in any of the lipoprotein classes. Intralipid infusion for periods up to 3 days results in a limited further displacement of endogenous phospholipids by exogenous lipids in the plasma lipoproteins, but a complete substitution was not achieved because of a continued secretion of lipoproteins containing endogenous phospholipids. The infusion of Intralipid led to a significant increase in the proportion of the phospholipid and free sterol in all lipoproteins, which decreased the calculated diameter of the particles by about one-half. Only minor changes were seen in the lipid to protein ratios of the lipoproteins and in their apoprotein composition.