Metabolism of low- and high-density-lipoprotein-free cholesterol in rats fed high-fat diets.

The regulating process of cholesterol in the liver was studied in relation to its exogenous contribution in the rats fed high-fat (28%) high-cholesterol (1.2%) diets rich in saturated (S) fat (lard) or polyunsaturated (PU) fat (corn oil). Accordingly, the fate of 14C free cholesterol originating from high- or low-density lipoproteins (LDL) was examined in the biliary, hepatic and plasmatic lipids, as well as the activity of two key enzymes in the metabolism of lipoproteins: lipoprotein lipase (LPL) and lecithin cholesterol acyl transferase (LCAT). The LPL activity increased in the S diet, in comparison to the PU diet or to a low fat (6%) control (C) diet and the LCAT activity increased but not significantly in the PU diet. In bile the secretion of 14C-cholesterol and 14C-bile salts originating from 14C-cholesterol-HDL increased in the S diet compared to the PU diet and a C diet [previous results]. S and PU diets increased to the same extent the hepatic storage of 14C-esterified cholesterol originating from LDL, compared to the C diet. This cholesterol would contribute to a greater extent to the hepatic synthesis of the lipoproteins destined for the plasma in the case of the S diet than that of PU diet. These results may be explained by the adaptation of hepatic acyl cholesterol acyl transferase and cholesterolesterase to both high-fat-diet enzymes acting simultaneously on the two free and esterified cholesterol compartments. It resulted in an important redistribution of the cholesterol of these two compartments between plasma, bile and liver.