Do iodinated fatty acids undergo a nonspecific deiodination in the myocardium?

The intracellular and subcellular distribution of 16-(123I)-iodo-9-hexadecenoic acid were studied in isolated rat hearts, perfused with or without glucose. At various time intervals after injection, cardiac lipids were extracted and the activity was determined for all fractions and all lipid classes. The total cardiac activity was maximal within 1 min postinjection and most of the activity was in the aqueous phase. The presence of glucose in the perfusion medium induced an increase of total cardiac and organic fraction activities. In the latter fraction, activity was very low for FFA, but high for triglycerides (TG), and especially polar lipids. The presence of an exogenous substrate, led to a more active esterification of fatty acids. Coronary effluent analysis showed, in the hydrophilic phase, a lower activity spike in the presence than in the absence of glucose. In the mitochondrial fraction most activity occurred in the organic phase, especially as polar lipids. In the nonmitochondrial fraction, activity was much higher in the aqueous phase. At 90 s postinjection of 1-14C-palmitic acid, over 80% of the myocardial activity was found in the hydrophilic fraction, which indicates, as for the iodo-fatty acid (IFA), an immediate and important oxidation, especially without glucose. These data seem to prove that IFA is taken up by the myocardial cell, subsequently enters the mitochondria and, without an early deiodination, is oxidized with iodide release. Changes in IFA metabolism, consecutive to modifications of glucose concentration in the perfusion medium can be observed by external detection of the myocardial activity curve. Omega-Iodinated fatty acids do not undergo a nonspecific deiodination and are therefore well suited for an external study of myocardial metabolism.