title: Conversion of alpha-linolenate to docosahexaenoate is not depressed by high dietary levels of linoleate in young rats: tracer evidence using high precision mass spectrometry.
abstract: The conversion of alpha-linolenate (18:3n-3) to docosahexaenoate (22:6n-3) in the presence of low and high dietary levels of linoleate (18:2n-6) is reported in young rats using [U-13C]-alpha-linolenic acid (18:2n-3*) and high precision gas chromatography-combustion isotope ratio mass spectrometry (GCC-IRMS). After consuming an 18:3n-3-deficient diet for 4 weeks, dams were bred and assigned to one of three diet groups: a) 2 g 18:3n-3/kg diet and 17 g 18:2n-6/kg diet (Lo-18:2), b) 2 g 18:3n-3/kg diet and 140 g 18:2n-6/kg diet (Hi-18:2), or c) essential fatty acid-deficient diet (EFAD). Pups were weaned to the maternal diets. At 42 days of age, pups were gavaged with 1 mg 18:3n-3*, and killed 48 h later. Fatty acid composition of liver reflected the diets to a greater extent than did the brain, and 22:5n-6 replaced 22:6n-3 in the brain. About 80% of the label in liver, brain, and plasma was found as 22:6n-3* for the replete groups. The enrichment pattern was similar in liver and plasma except for 18:3n-3, which was higher in liver. Total label detected was 4-fold higher in the EFAD livers and 2-fold higher in the EFAD brains than in the other groups, which were indistinguishable. Conversion of 18:3n-3* to 22:6n-3* was greater in livers from the Hi-18:2 group than from the Lo-18:2 group (P < 0.05). Estimates of overall label recovery in liver and brain were consistent with literature values. These data indicate that high dietary levels of 18:2n-6 do not inhibit conversion of a single dose of 18:3n-3 to 22:6n-3 in young rats, and demonstrate the applicability of high precision GCC-IRMS to fatty acid tracer studies.
authors.affiliation: Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853, USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Sheaff
authors.forename: H M
authors.initials: HM
authors.lastname: Su
authors.forename: L A
authors.initials: LA
authors.lastname: Keswick
authors.forename: J T
authors.initials: JT
authors.lastname: Brenna
mesh_terms: D000818:Animals; D001711:Biotransformation; D001835:Body Weight; D002247:Carbon Isotopes; D003864:Depression, Chemical; D004041:Dietary Fats / Q000493:pharmacokinetics*; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017962:alpha-Linolenic Acid / Q000493:pharmacokinetics*
chemical_list: D002247:Carbon Isotopes; D004041:Dietary Fats; D005227:Fatty Acids; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids