Quantitative contributions of diet and liver synthesis to docosahexaenoic acid homeostasis.
Dietary requirements for maintaining brain and heart docosahexaenoic acid (DHA, 22:6n-3) homeostasis are not agreed on, in part because rates of liver DHA synthesis from circulating alpha-linolenic acid (alpha-LNA, 18:3n-3) have not been quantified. These rates can be estimated using intravenous radiotracer- or heavy isotope-labeled alpha-LNA infusion. In adult unanesthetized male rats, such infusion shows that liver synthesis-secretion rates of DHA from alpha-LNA markedly exceed brain and heart DHA synthesis rates and the brain DHA consumption rate, and that liver but not heart or brain synthesis is upregulated when dietary n-3 PUFA content is reduced. These rate differences reflect much higher expression of DHA-synthesizing enzymes in liver, and upregulation of liver but not heart or brain enzyme expression by reduced dietary n-3 PUFA content. A noninvasive intravenous [U-(13)C]alpha-LNA infusion method that produces steady-state liver tracer metabolism gives exact liver DHA synthesis-secretion rates and could be extended for human studies.
Rapoport
Stanley I
SI
Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA. sir@helix.nih.gov
Igarashi
Miki
M
Gao
Fei
F
D000818:Animals; D002247:Carbon Isotopes / Q000737:chemistry; D004032:Diet; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000737:chemistry
D002247:Carbon Isotopes; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids