Plasma lipoproteins in rats with experimental biliary obstruction. I. A chemical study.

Acute biliary obstruction in the rat is associated with striking alterations of the plasma level and the physico-chemical properties of plasma lipoproteins. 1. The level of very low density lipproteins (VLDL) in plasma increases from 2 to 3 fold. The chemical composition of VLDL is characterized by a high content of phospholipids and cholesterol and by a diminution of the relative content of triacylglycerols and protein. On cellulose acetate electrophoresis, VLDL show a beta-mobility. 2. The plasma concentration of low density lipoproteins (1.019--1.063 g/ml, LDL2) increases several fold above the control level. Phospholipids and unesterified cholesterol are the major components of this fraction which contains only a minute amount of cholesteryl ester (4%) and triacylglycerols (10%). LDL2 contain a component which migrates to the cathode in 1% agar gel electrophoresis. Separation of LDL2 by gel filtration on 2% agarose column results in the identification of three subfractions. Subfraction I contains a large proportion of cholesterol and triacylgylcerols, subfraction II is rich in unesterified cholesterol and phospholipids whereas subfraction III has a chemical composition fairly similar to that of the control LDL2. 3. The level of high density lipoproteins (HDL) also increases after bile duct ligation. The chemical composition of HDL2 (1.063-1.125 g/ml) is characterized by a high content of unesterified cholesterol and phospholipids and by a remarkable reduction in the content of cholesteryl esters and protein.