Metabolism of fatty acids in the isolated perfused rat heart

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1. 1. Rat hearts were perfused with a medium containing two different radioactive fatty acids, labeled with 14C and 3H, respectively. 2. 2. No preference was found for the extraction from the medium of the following acids tested: palmitic, stearic, oleic and linoleic acid. However, the distribution of these acids in the heart lipids differed. 3. 3. In the neutral lipids of the heart, over 96% of the fatty acids incorporated were found in the triglyceride fraction. In this fraction the incorporation of palmitic acid exceeded that of its competitors: stearic, oleic and linoleic acids. 4. 4. In the phospholipids of the heart, the lecithin fraction contained over 70% of the fatty acids incorporated. Here, stearic and linoleic acid incorporation exceeded that of palmitic acid, while oleic acid was incorporated to a similar extent. 5. 5. In the lecithin molecule labeled linoleic acid was confined practically to the β-position, while labeled palmitic acid was distributed evenly between the α- and β-positions. 6. 6. A faster turnover of linoleic acid than of palmitic acid in the lecithin molecule was suggested by results obtained from perfusing the prelabeled heart without radioactive substrates. The presence of enzyme systems in the myocardium which remove fatty acids from the β-position of lecithin ( i.e., primarily linoleic acid) was demonstrated. 7. 7. The rate of fatty acid incorporation into lipids was independent of the heart beat. 8. 8. Lowering of the surrounding temperature decreased the esterification of palmitic acid into neutral glycerides to a greater extent than into phospholipids.