In vivo esterification of a synthetic ¹²⁵I-labelled fatty acid into cardiac glycerolipids

Recent studies have demonstrated that fatty acids can be successfully utilized as myocardial imaging agents. ¹²⁵I-paraphenylpentadecanoic acid (IPPA), a synthetic fatty acid, accumulated within the myocardium and can be visualized by conventional gamma scintigraphy. To determine if IPPA was incorporated into cardiac lipids in a pattern similar to palmitate, IPPA was purified by liquid chromatography, bound to fat-free albumin, and administered by intravenous injection to male Sprague-Dawley rats. After 2.5, 5, 10, and 30 min, the hearts were excised, and the lipids were extracted in chloroform-methanol. The uptake of IPPA into the myocardium reached a maximal value after 2.5 min, and 95% of the ¹²⁵I was found in the cardiac lipid fraction after chromatographic separation. Over 65% of the IPPA was found in cardiac triglycerides, whereas approximately 10% was present in membrane phospholipids (predominantly phosphatidylcholine and phosphatidylethanolamine). This pattern of IPPA incorporation is similar to that reported for intravenously administered [³H]palmitate. The rate of turnover of IPPA present in the triglyceride fraction was threefold faster than the rate of the IPPA which was incorporated into membrane lipids. At all time periods examined, the methanol-water soluble end products of IPPA oxidation did not account for more than 5% of the total IPPA present within the myocardium. The present study indicates that IPPA is incorporated primarily into triglycerides and other cardiac lipids in a pattern similar to palmitate.