Biosynthesis and secretion of triacylglycerol in rat liver after partial hepatectomy.

Partially hepatectomized rats were used to investigate the mechanism of fatty-liver development in the regenerating rat liver. After partial hepatectomy the amount of hepatic triacylglycerol increased by almost 4-fold compared with sham-operated rats. The activities of both cytosolic and microsomal phosphatidate phosphohydrolase were enhanced at 12 h after surgery. The activity of diacylglycerol acyltransferase was increased at a later stage of regeneration. Analysis of plasma lipoproteins showed a significant decrease of lipids associated with very-low-density lipoproteins (VLDL). Relative to control, the rate of hepatic triacylglycerol synthesis from [3H]glycerol in vivo was stimulated at 22 h after partial liver resection. However, secretion of glycerol-labelled triacylglycerol in VLDL was the same in control and hepatectomized rats. In cultures of hepatocytes from hepatectomized donor rats, the concentration of triacylglycerol and the biosynthesis of this lipid from [3H]glycerol or from [3H]oleate were enhanced. The secretion of total triacylglycerol into the medium was not affected, resulting in a net accumulation of intracellular triacylglycerol. The rate of secretion of leucine-labelled apolipoproteins B and E associated with VLDL was similar in cell cultures from hepatectomized and sham-operated rats. The results of this study show that the enhancement of the biosynthesis of triacylglycerol in hepatectomized livers is not accompanied by an increase of the secretion of VLDL.