[3-13C] γ-linolenic acid: A new probe for 13C nuclear magnetic resonance studies of arachidonic acid synthesis in the suckling rat |
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Authors: | S C Cunnane G Moine S S Likhodii J Vogt T N Corso J T Brenna H Demmelmair B Koletzko K -H Tovar G Kohn G Sawatzki R Muggli |
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Affiliation: | (1) Vitamins and Fine Chemicals Division, F. Hoffmann-La Roche Ltd., Basel, Switzerland;(2) Department of Nutritional Sciences, Cornell University, Ithaca, New York;(3) Kinderpoliklinik, University of Munich, Munich, Germany;(4) Milupa AG, Friedrichsdorf, Germany;(5) Department of Nutritional Sciences, University of Toronto, 150 College St., M5S 3E2 Toronto, Canada |
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Abstract: | Our objective was to develop a suitable probe to study metabolism of polyunsaturated fatty acids by 13C nuclear magnetic resonance (NMR) in the suckling rat pup. 3-13C] γ-Linolenic acid was chemically synthesized, and a 20 mg (Experiment 1) or 5 mg (Experiment 2) dose was injected into the
stomachs of 6–10-day-old suckling rat pups that were then killed over a 192 h (8 d) time course. 13C NMR showed that 13C in γ-linolenate peaked in liver total lipids by 12-h post-dosing and that 5-13C]-arachidonic acid peaked in both brain and liver total lipids 48–96 h post-dosing. 13C enrichment in brain γ-linolenic acid was not detected by NMR, but gas chromatography-combustion-isotope ratio mass spectrometry
showed that its mass enrichment in brain phospholipids at 48–96 h post-dosing was 1–2% of that in brain arachidonic acid.
13C was present in liver and brain cholesterol and in perchloric acid-extractable water-soluble metabolites in the brain, liver
and carcass. We conclude that low but measurable amounts of exogenous γ-linolenic acid do access the suckling rat brain in vivo. The slow time course of 5-13C] arachidonic acid appearance in the brain suggests most of it was probably transported there after synthesis elsewhere,
probably in the liver. Some carbon from γ-linolenic acid is also incorporated into lipid products other than n−6 long-chain
polyunsaturated fatty acids. |
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