Chylomicron metabolism by the isolated perfused mouse heart

The catabolism of rat chylomicrons, labeled in their triacylglycerol (TG) c omponent, was investigated using perfused working mouse hearts. Perfusion o f mouse hearts with heparin increased lipoprotein lipase (LPL) activity in the perfusate. This heparin-releasable LPL pool remained constant over a va riety of experimental conditions, including workload and fatty acid concent rations, making the mouse heart a suitable model to study chylomicron catab olism. Endothelium-bound LPL hydrolyzed radiolabeled H-3-labeled chylomicro ns (0.4 mM TG); the fate of LPL-derived H-3-labeled fatty acids was split e venly between oxidation (production of (H2O)-H-3) and esterification (incor poration into tissue lipids, mainly TG). In comparison, the oxidation of 0. 4 mM [H-3] palmitate complexed to albumin was fourfold greater than esterif ication into tissue lipids. Surprisingly, the addition of unlabeled palmita te (0.4 or 1.2 mM) to perfusions with H-3-chylomicrons did not affect the f ate (either oxidation or esterification) of LPL-derived H-3-fatty acids. Th ese results suggest that fatty acids produced from lipoprotein hydrolysis b y the action of LPL and fatty acids from a fatty acid-albumin complex do no t enter a common metabolic pool in the heart.