Metabolism of palmitate in perfused rat liver. Isolation of subcellular fractions containing triacylglycerol

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Abstract
Metabolism of [1-14C]palmitate in rat liver was studied in a single-pass perfusion system at concentrations of 0.2 or 1 mM. After perfusion the liver was homogenized and floating fat isolated. Incorporation of [1-14C]palmitate into triacylglycerol in this pool increased 9-fold when the palmitate concentration in the medium was increased from 0.2 to 1 mM. In time studies with 1 mM-[1-14C]palmitate, 75% of the total triacylglycerol accumulation occurred in this pool. The results support the concept that the floating-fat fraction contains the storage pool of triacylglycerol, i.e., the cytoplasmic lipid droplets. In a particulate preparation consisting mainly of mitochondria and microsomal fraction, the incorporation of [1-14C]palmitate into triacylglycerol was proportional to the fatty acid concentration. Triacylglycerol in the perfusate medium and in the particulate fraction was in isotopic equilibrium, which indicates that the particulate fraction contained the precursor pool for secreted triacylglycerol, i.e., the pool in endoplasmic reticulum and Golgi apparatus. Oxidation to labelled water-soluble products and to CO2 was increased 14-fold by the 5-fold increase in palmitate concentration.