title: In vivo conversion of 18- and 20-C essential fatty acids in rats using the multiple simultaneous stable isotope method.
abstract: An important question for mammalian nutrition is the relative efficiency of C18 versus C20 essential fatty acids (EFAs) for supporting the tissue composition of n-3 and n-6 pathway end products. One specific question is whether C22 EFAs are made available to tissues more effectively by dietary alpha-linolenic acid (18:3n-3) and linoleic acid (18:2n-6) or by dietary eicosapentaenoic acid (20:5n-3) and dihomo-gamma-linolenic acid (20:3n-6). To address this question in a direct manner, four stable isotope compounds were given simultaneously in a novel paradigm. A single oral dose of a mixture of 2H5-18:3n-3, 13C-U-20:5n-3, 13C-U-18:2n-6, and 2H5-20:3n-6 was administered to rats given a defined diet. There was a preferential in vivo conversion of arachidonic acid (20:4n-6) to docosatetraenoic acid (22:4n-6) and of 22:4n-6 to n-6 docosapentaenoic acid (22:5n-6) when the substrates originated from the C18 precursors. However, when the end products docosahexaenoic acid (22:6n-3) or 22:5n-6 were expressed as the total amount in the plasma compartment divided by the dosage, this parameter was 11-fold greater for 20:5n-3 than for 18:3n-3 and 14-fold greater for 20:3n-6 than for 18:2n-6. Thus, on a per dosage basis, the total amounts of n-3 and n-6 end products accreted in plasma were considerably greater for C20 EFA precursors relative to C18.
authors.affiliation: Section of Nutritional Neuroscience, Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, USA.
authors.forename: Yu Hong
authors.initials: YH
authors.lastname: Lin
authors.forename: Norman
authors.initials: N
authors.lastname: Salem
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002247:Carbon Isotopes; D003903:Deuterium; D004041:Dietary Fats / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D005227:Fatty Acids / Q000097:blood; D005228:Fatty Acids, Essential / Q000008:administration & dosage / Q000378:metabolism*; D015525:Fatty Acids, Omega-3 / Q000097:blood; D043371:Fatty Acids, Omega-6 / Q000097:blood; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D007553:Isotope Labeling; D007700:Kinetics; D019787:Linoleic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D002247:Carbon Isotopes; D004041:Dietary Fats; D005227:Fatty Acids; D005228:Fatty Acids, Essential; D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D017962:alpha-Linolenic Acid; D016718:Arachidonic Acid; D019787:Linoleic Acid; D003903:Deuterium; C026219:docosapentaenoic acid