Cholesterol Esterification Associated with High Density Lipoproteins in Cholesterol-fed Rabbit

Abstract

Plasma lecithin:cholesterol acyl transferase (LC AT) activity was measured in 10 normal and 10 hypercholesterolemic rabbits (2%-cholesterol diet) after removal of the bulk of very low and low density lipoproteins (VLDL, LDL), either by ultracentrifugation at density 1.063 g/ml or by heparin/manganese chloride precipitation. In normal rabbit the net esterification was 43.7 µmoles per liter plasma per hour in the whole plasma, 13.6 µmoles in the ultracentrifuged plasma, and 20.3 µmoles in the plasma treated by MnCl₂; in hypercholesterolemic rabbit, the LCAT activity was 38.6, 20.1 and 29.7 µmoles. respectively. While the relationship between the free cholesterol concentrations and the net esterification was obscured in the whole plasma, the correlation was significant in all the fractions of plasma depleted in VLDL and LDL. The difference between cholesterol esterification in ultracentrifuged plasma and MnCl₂-treated plasma could be due in part to the fact that some apolipoprotein(s) of high density lipoproteins is dissociated from the lipoprotein complex during ultracentrifugation. On the other hand, the higher net esterification associated with HDL in hypercholesterolemic plasma could be accounted for by the progressive enrichment with polar lipids which occurs in HDL upon cholesterol feeding: particles of high polar lipid content appear to be the best substrate for the LCAT reaction

Key Words:

• free cholesterol
• heparin
• hypercholesterolemia
• lecithin: cholesterol acyl transferase
• manganese choloride