Abstract
The role of very low density lipoproteins (VLDL) in the energy metabolism of conscious, 24-hr fasted rats was studied. VLDL labeled with [2-3H]glycerol and [1-14C]palmitate were infused into the rats, along with [1-13C]palmitate bound to albumin and d-8-glycerol, and various metabolic factors were assessed. The rates of appearance in plasma of fatty acids in VLDL and albumin-bound free fatty acids (FFA) were about equal, on a molar basis, and only a small fraction of the FFA flux was derived from VLDL. The rate of direct oxidation of the fatty acids from VLDL was 4.4 +/- 0.9 mumol of FA/kg X min, as compared with the value of 4.0 +/- 0.42 mumol of FA/kg X min for plasma FFA. Four percent of the plasma glycerol flux was derived from VLDL. Thus, the direct oxidation of fatty acids in VLDL played an important role in the energy metabolism of the rats, accounting for a percentage of the total CO2 production that was equal to the amount that arose from the oxidation of plasma FFA. The oxidation of VLDL-fatty acids did not involve prior entry of the fatty acids into the plasma FFA pool to any significant extent.
Highlights
The role of very low density lipoproteins(VLDL) in the energy metabolism of conscious, 24-hr fasted rats was studied
The direct oxidagon of fatty acids in VLDL played an important role in the energy metabolism of the rats, accounting for a percentage of the total C 0 2 production that was equal to the amount that arose from the oxidation of plasma free fatty acids (FFA)
The values reported for the rate of VLDL release in rats fasted for 24 hr have ranged widely(3, 4, 12)
Summary
The role of very low density lipoproteins(VLDL) in the energy metabolism of conscious, 24-hr fasted rats was studied. The direct oxidagon of fatty acids in VLDL played an important role in the energy metabolism of the rats, accounting for a percentage of the total C 0 2 production that was equal to the amount that arose from the oxidation of plasma FFA. When a "C-labeled fatty acid (palmitate) was used to calculate the rate of plasma free fatty acid (FFA) oxidation, only about one-third of the total rate of fat oxidation, as determined by indirect calorimetry, could be accounted for (1). The existence of an intramuscular fat pool that provides muscle with substrate for energy metabolism directly has been proposed as an explanation for this finding (2) Another possible source of fat for energy metabolism is the circulating very low density lipoproteins (VLDL).
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