Effect of a high-fat diet on the incorporation of stored triacylglycerol into hepatic VLDL

Triacylglycerol (TG) stored in cytoplasmic lipid droplets of hepatocytes was labeled by in vivo [1-14C]oleic acid injection to study the effect of a high-fat diet on its incorporation into very-low-density lipoproteins (VLDL). Compared with the control diet, hepatocytes of fat-fed rats 1) contained 7.6 times more cytoplasmic (floating fat) TG and 1.9 times more endoplasmic reticulum (microsomal) TG; 2) had 8 and 6 times lower TG specific activities in cytoplasm and endoplasmic reticulum, respectively; 3) incorporated 22% less 14C label into hepatocyte esterified lipids (TG, cholesterol, phospholipid); 4) secreted 48 and 33% less radioactive and total VLDL-TG, respectively; 5) oxidized more cytoplasmic TG-fatty acid (FA); and 6) showed a 50% decreased total utilization of stored TG-FA. With both diets, the lysosomal inhibitor chloroquine concomitantly decreased productions of labeled VLDL-TG, C02, and acid-soluble oxidation products. The decreased incorporation of store TG into VLDL-TG appreciably contributes to the overall inhibition of hepatic VLDL secretion by fat feeding. It appears to related to the decreased mobilization rate of stored TG and increased channelling toward oxidation