Characterization of essential fatty acid metabolism using the stable isotope tracer technique and gas chromatography/ mass spectrometric assay

Abstract

To better understand essential fatty acid metabolism, several in vivo and in vitro studies have been performed. Diet controlled rats were orally administrated a mixture of two or more labeled fatty acids: d5‐linoleate, ‐linolenate, ‐dihomo‐gamma‐linolenate (DGLA), and/or 13C‐U‐ linoleate or eicosapentaenoate. GC/MS NCI assay was employed to measure the isotopic precursors, their respective metabolites in rat organs over a time‐course from 4 h up to 25 d. Results and conclusions. 1. Only 2.6% and 6% of linoleate and linolenate, respectively, were elongated and desaturated in rats with about 78% being utilized for beta‐oxidation, excretion, or other loss and 16~18% was stored in tissues, mainly adipose, as the precursor itself. 2. Eicosapentaenoate was a more efficient substrate for docosahexaenoate (DHA) than linolenate; similarly, DGLA is a better substrate for arachidonate and n‐6 docosapentanoate than was linoleate. 3. Dietary DHA is the primary source of brain DHA. 4. Preformed DHA markedly decreased the accumulation of de novo biosynthesized DHA and n‐6 docosapentaenoate in liver, plasma, heart and brain; but no significant differences in rat hepatocytes delta‐5 or ‐6 desaturase activities have been observed. Decreased accumulation of newly‐synthesized DHA by dietary DHA may relate to increased DHA catabolism.This project was funded by the DICBR, NIAAA, NIH.