Metabolism of Tripalmitin-1-C14-Labeled Serum Low-Density Lipoproteins by the Isolated Perfused Goat Liver ,

Abstract

After perfusing for 2 hr, the defibrinated perfusate, liver, and bile were analyzed for distribution of radioactivity and changes in lipid concentrations and fatty acid composition. It was shown that more than 80% of the activity from tripalmitin-1-C14-labeled serum low-density lipoproteins (LDL) was taken up and retained by the liver, and 2% of the activity was transferred to the serum high-density lipoproteins (HDL). Isotopic flux also occurred to the serum protein-bound nonesterified fatty acids, blood cells, bile, and CO2. C14 was of highest specific activity, generally, in the triglycerides, but was present also in the other lipid classes, including sterols. A general decrease in the concentration of total lipids and lipid classes occurred during perfusion. However, slight gravimetric increases were seen in the hydrocarbon fractions. Slight, but pervasive, changes in saturation occurred in lipid classes of the HDL and LDL; marked changes were seen in lipid classes of the blood cells. Changes in saturation usually involved shifts in the proportions of palmitate, stearate, and oleate. HDL and LDL comprised 51 and 49%, respectively, of goat serum total lipids. HDL lipid classes were similar to those of the LDL in fatty acid composition. Triglycerides, however, were more saturated in the LDL. Oleate was the major unsaturated fatty acid in most lipid classes. Phospholipids represented the major portion of liver tissue lipids and contained 49% stearate.