The catabolism of rat chylomicrons, labeled in their triacylglycerol (TG) component, was investigated using perfused working mouse hearts. Perfusion of mouse hearts with heparin increased lipoprotein lipase (LPL) activity in the perfusate. This heparin-releasable LPL pool remained constant over a variety of experimental conditions, including workload and fatty acid concentrations, making the mouse heart a suitable model to study chylomicron catabolism. Endothelium-bound LPL hydrolyzed radiolabeled 3H-labeled chylomicrons (0.4 mM TG); the fate of LPL-derived 3H-labeled fatty acids was split evenly between oxidation (production of3H2O) and esterification (incorporation into tissue lipids, mainly TG). In comparison, the oxidation of 0.4 mM [3H]palmitate complexed to albumin was fourfold greater than esterification into tissue lipids. Surprisingly, the addition of unlabeled palmitate (0.4 or 1.2 mM) to perfusions with3H-chylomicrons did not affect the fate (either oxidation or esterification) of LPL-derived 3H-fatty acids. These results suggest that fatty acids produced from lipoprotein hydrolysis by the action of LPL and fatty acids from a fatty acid-albumin complex do not enter a common metabolic pool in the heart.
FATTY ACID COMPONENTS OF RAT-TISSUE LIPIDS