Abstract
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 alpha-linolenic acid (alpha-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-(13)C]alpha-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 [(13)C]DHA, [(13)C]EPA, and [(13)C]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 mumol/day, respectively. The DHA synthesis rate exceeded the published daily rat brain DHA consumption rate by 30-fold, suggesting that liver synthesis from alpha-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.
Highlights
W nously for 2 h and measuring labeled and unlabeled n-3 A 4 polyunsaturated fatty acids (PUFAs) in arterial plasma using negative chemical ionization 1 GC-MS
One reason for this controversy may be that the liver synthesis rate of Docosahexaenoic acid (DHA) from a-linolenic acid (a-LNA, 18:3 n-3), which is obtained from dietary plant oils, is uncertain
A: Labeled n-3 PUFA esterified arterial plasma concentrations 3 plasma volume plotted against time for experiment in which 3 mmol/100g [13C]a-LNA was infused intravenously for 120 min in a rat, and best-fit
Summary
At fixed times during infusion, esterified and unesterified arterial plasma concentrations of [13C]a-LNA, [13C]EPA, [13C]docosapentaenoic acid ([13C]DPA), and [13C]DHA were measured using negative chemical ionization GC-MS (NCI-GC-MS). Diheptadecanoate phosphatidylcholine (Di-17:0 PC), free heptaH 0 decanoic acid (17:0), n-3 PUFA standards such as a-LNA, EPA, T 1 DPA, and DHA, TLC standards for cholesterol, unesterified FAs, I il phospholipids, triacylglycerol, cholesteryl esters, pentafluorobenzyl (PFB) bromide, and diisopropylamine were purchased. This high-sensitivity detection allows detailed fusion has begun (min), k1,i is the steady-state synthesis-secretion coefficient of esterified longer-chain labeled PUFA i (nmol/min), studies of tissue essential FA metabolism [36, 37, 39, 40]
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