Metabolism of beta-methyl[1- 11C]heptadecanoic acid in canine myocardium

Abstract

To assess the contributions of metabolism to CO 2 and back-diffusion of nonmetabolized tracer to total clearance of beta-methyl[1- 11C]heptadecanoic acid ([1- 11C]BMHDA) from myocardium and its distribution into lipid pools, 10–15 mCi of [1- 11C]BMHDA were rapidly infused into the circumflex coronary artery of seven open-chest dogs. Externally detected clearance of myocardial 11C-activity was protracted ( t 1 2 = 41 ± 18 min ) with over 50% of extracted tracer retained in tissue after 20 min. Efflux of extracted [1- 11C]BMHDA between 5 and 20 min was comprised of both 11CO 2 (16.5 ± 15.2%) and nonmetabolized [ 11C]BMHDA (24.6 ± 11.5%). At 20 min, 11C-activity in lipid was distributed primarily between triglyceride (47 ± 16% of total) and phospholipid (39 ± 17%) pools. Partial oxidation to 11CO 2 and partitioning into more than one lipid pool are likely to hinder evaluation of fatty acid metabolism based on residue detection of [1- 11C]BMHDA with tomography.