Fate of tritium-labeled carnitine administered to dogs and rats

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Abstract
Dl-Carnitine hydrochloride, tritiated nonspecifically, was purified and shown to have the same chemical and biological properties as the original compound (ß-hydroxy, γ-trimethylammonium butyrate). About one-third of administered material was excreted in urine during a 7-hr period following the intravenous injection of carnitine HCl (2 mg/kg) to dogs. Tritium not excreted appeared primarily in the trichloroacetic acid (TCA)-soluble fraction of various tissues, with approximately half that administered being found in skeletal muscle. The concentrations of tritium in TCA-soluble fractions of all organs examined except brain were 4–30 times higher than plasma concentrations. No evidence of carnitine degradation was found. The tritiated material in TCA-soluble extracts moved as single peaks in three different chromatographic systems, having the same RF values as those of known samples of carnitine. Tritium in chloroform-soluble fractions accounted for less than 1% of that administered. Of the organs examined, liver had the highest relative amount of incorporation of tritium into lipids, with all activity being found in unidentified phospholipids, chiefly in the lecithin fraction. The possible physiological significance of carnitine in muscle is briefly discussed.