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Journal of Lipid Research, Vol. 50, 749-758, April 2009
Copyright © 2009 by American Society for Biochemistry and Molecular Biology

Methods

Whole-body synthesis-secretion rates of long-chain n-3 PUFAs from circulating unesterified -linolenic acid in unanesthetized rats

Fei Gao^1,*, Dale Kiesewetter, Lisa Chang^*, Kaizong Ma^*, Jane M. Bell^*, Stanley I. Rapoport^* and Miki Igarashi^*

^* Brain Physiology and Metabolism Section, National Institute on Aging, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892
Positron Emission Tomography Radiochemistry Group, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892

This research was supported by the Intramural Research Programs of the National Institutes on Aging and of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD.

Published, JLR Papers in Press, December 11, 2008.

¹ To whom correspondence should be addressed. e-mail: gaof{at}mail.nih.gov

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), long-chain n-3 PUFAs important for brain and heart function, can be obtained from dietary fish products or by liver synthesis from -linolenic acid (-LNA). Their daily human dietary requirements are not clear, and their liver synthesis rates in humans and nonhumans are unknown. We estimated whole-body (presumably liver) synthesis rates in unanesthetized rats by infusing [U-¹³C]-LNA intravenously for 2 h and measuring labeled and unlabeled n-3 PUFA in arterial plasma using negative chemical ionization GC-MS. Newly synthesized esterified [¹³C]DHA, [¹³C]EPA, and [¹³C]docosapentaenoic acid (DPA) appeared in arterial plasma after 60 min of infusion, then their concentrations rose in an S-shaped manner. Esterified concentration x plasma volume data were fit with a sigmoidal equation, whose peak first derivatives provided synthesis rates of unlabeled EPA, DPA, and DHA equal to 8.40, 6.27, and 9.84 µmol/day, respectively. The DHA synthesis rate exceeded the published daily rat brain DHA consumption rate by 30-fold, suggesting that liver synthesis from -LNA could maintain brain DHA homeostasis were DHA absent from the diet. This stable isotope infusion method could be used to quantify whole-body DHA synthesis rates in human subjects.

Supplementary key words docosahexaenoic acid • stable isotopes • liver • esterified • rat • kinetics

Abbreviations: DHA, docosahexaenoic acid; DPA, docosapentaenoic acid; EPA, eicosapentaenoic acid; -LNA, -linolenic acid; NCI, negative chemical ionization; PFB, pentafluorobenzyl

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				F. Gao, D. Kiesewetter, L. Chang, K. Ma, S. I. Rapoport, and M. Igarashi Whole-body synthesis secretion of docosahexaenoic acid from circulating eicosapentaenoic acid in unanesthetized rats J. Lipid Res., December 1, 2009; 50(12): 2463 - 2470. [Abstract] [Full Text] [PDF]