title: Whole-Body Docosahexaenoic Acid Synthesis-Secretion Rates in Rats Are Constant across a Large Range of Dietary α-Linolenic Acid Intakes.
abstract: Docosahexaenoic acid (DHA) is an ω-3 (n-3) polyunsaturated fatty acid (PUFA) thought to be important for brain function. Although the main dietary source of DHA is fish, DHA can also be synthesized from α-linolenic acid (ALA), which is derived from plants. Enzymes involved in DHA synthesis are also active toward ω-6 (n-6) PUFAs to synthesize docosapentaenoic acid n-6 (DPAn-6). It is unclear whether DHA synthesis from ALA is sufficient to maintain brain DHA.
  
  
  
  The objective of this study was to determine how different amounts of dietary ALA would affect whole-body DHA and DPAn-6 synthesis rates.
  
  
  
  Male Long-Evans rats were fed an ALA-deficient diet (ALA-D), an ALA-adequate (ALA-A) diet, or a high-ALA (ALA-H) diet for 8 wk from weaning. Dietary ALA concentrations were 0.07%, 3%, and 10% of the fatty acids, and ALA was the only dietary PUFA that differed between the diets. After 8 wk, steady-state stable isotope infusion of labeled ALA and linoleic acid (LA) was performed to determine the in vivo synthesis-secretion rates of DHA and DPAn-6.
  
  
  
  Rats fed the ALA-A diet had an ∼2-fold greater capacity to synthesize DHA than did rats fed the ALA-H and ALA-D diets, and a DHA synthesis rate that was similar to that of rats fed the ALA-H diet. However, rats fed the ALA-D diet had a 750% lower DHA synthesis rate than rats fed the ALA-A and ALA-H diets. Despite enrichment into arachidonic acid, we did not detect any labeled LA appearing as DPAn-6.
  
  
  
  Increasing dietary ALA from 3% to 10% of fatty acids did not increase DHA synthesis rates, because of a decreased capacity to synthesize DHA in rats fed the ALA-H diet. Tissue concentrations of DPAn-6 may be explained at least in part by longer plasma half-lives.
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and.
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Domenichiello
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and.
authors.forename: Alex P
authors.initials: AP
authors.lastname: Kitson
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and.
authors.forename: Adam H
authors.initials: AH
authors.lastname: Metherel
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and.
authors.forename: Chuck T
authors.initials: CT
authors.lastname: Chen
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Hopperton
authors.affiliation: Bunge Ltd., New York, NY.
authors.forename: P Mark
authors.initials: PM
authors.lastname: Stavro
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada; and richard.bazinet@utoronto.ca.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Bazinet
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001834:Body Water; D004032:Diet / Q000662:veterinary*; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005231:Fatty Acids, Unsaturated / Q000097:blood; D008297:Male; D051381:Rats; D020318:Rats, Long-Evans; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D005231:Fatty Acids, Unsaturated; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids
keywords: docosahexaenoic acid; kinetics; synthesis; α-linolenic acid; ω-3 PUFA