[Lipid concentrations in liver cell fractions in the rat in diet induced obesity]

The changes of lipid parameters induced in male Wistar rats by feeding a high-fat diet for several weeks were studied in cell fractions of the liver. For this purpose subcellular fractionations of liver tissue from 12-week-old animals receiving food containing, respectively, 3% fat (controls) and 50% fat, were performed by means of differential centrifugation, and the lipids in the cell fractions were determined quantitatively. The levels of triglycerides and cholesteryl esters both in total liver and in the cell fractions had risen several fold against the controls. Most of the accumulated lipids were retrieved in the cytosolic supernatant. In contrast, for the phospholipids and the free cholesterol only a slight increase in free cholesterol was observed in total liver, and increases of both lipids had occurred in the cytosolic supernatant, while the particulate fractions showed no alterations. It is pointed out in the discussion that the accumulation of triglycerides and cholesteryl esters in the liver largely concerns the particulate fractions too (observed so far in the literature only for single particulate fractions), which might be of interest for the function of the cell nucleus, the mitochondria and the endoplasmatic reticulum. The increase of phospholipids and free cholesterol in the supernatant has to be considered not only as a passive process of deposition, but could represent necessary contributions to the building up of lipid droplets in the cytosol during deposition of triglycerides and cholesterol in this region of the cell. The studies confirm that the fatty degeneration of the liver, true, is always the result of triglyceride accumulation but that, under certain conditions, cholesterol is also enriched in the form of its esters.