The myocardial elimination rate of radioiodinated heptadecanoic acid

To clarify the mechanism of the elimination of radioactivity after administration of radioiodinated heptadecanoic acid, dogs with and without coronary occlusion were studied. In myocardial tissue samples of normal and ischemic myocardium, the proportions of free radioiodide, radioiodinated heptadecanoic acid, and radioiodinated lipids were determined. Five minutes after intravenous injection of heptadecanoic acid 69% of the radioactivity was present as free iodine, 7% as unaltered heptadecanoic acid, and 24% as lipids. Even in ischemic myocardium 41% was free iodine and 47% lipids. After 2 h free iodine decreased to 48% and lipids increased to 44%. These results indicate that beta-oxidation is not the rate-limiting step in the elimination rate of heptadecanoic acid.