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1 Laboratoire de Physiopathologie Métabolique et Rénale and the 2 Centre de Recherche en Nutrition Humaine de Lyon, 69008 Lyon, France
To measure
1) the contribution of hepatic de
novo lipogenesis (DNL) and plasma free fatty acid (FFA)
reesterification to plasma triglyceride (TG) secretion, and
2) the role of oxidation and hepatic
and extrahepatic reesterification in FFA utilization, five normal
subjects drank deuterated water and were infused (postabsorptive state)
with [1-13C]palmitate
and
[1,2,3-2H5]glycerol.
Total lipid oxidation (Lox) was
measured by indirect calorimetry. FFA oxidation (2.76 ± 0.65 µmol · kg
1 · min
1)
accounted for 45% of FFA turnover rate
(Rt) (1.04 µmol · kg
1 · min
1)
and 91% of Lox; FFA
reesterification was 3.27 ± 0.54 µmol · kg
1 · min
1.
Fractional and absolute TG Rt were
0.21 ± 0.02 h
1 and 0.11 ± 0.05 µmol · kg
1 · min
1.
DNL accounted for 3.9 ± 0.9% of TG secretion, and hepatic FFA reesterification accounted for 49.4 ± 5.7%; this last
process represented a utilization of FFA of 0.16 ± 0.02 µmol · kg
1 · min
1.
We conclude that, in the postabsorptive state,
1) DNL and FFA reesterification
account for only 50-55% of TG secretion, the remaining presumably
being provided by stored lipids or lipoproteins taken up by liver,
2) most reesterification occurs in
extrahepatic tissues, and 3)
oxidation and reesterification each contribute about one-half to FFA
utilization; FFA oxidation accounts for almost all
Lox.
mass spectrometry; indirect calorimetry; oxidation; stable isotopes; lipids
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