Source of fat oxidation in exercising dogs

Abstract

Dogs with indwelling arterial and venous catheters ran on a treadmill for 30–40 min. Palmitate-1-C14 was infused intravenously. The rate of FFA uptake increased linearly with FFA concentration during rest and exercise. At rest 20– 22% of the FFA uptake was oxidized; during exercise this figure rose to 80–90%. About 50% of the fat-CO2 could be ascribed to immediate oxidation of plasma FFA. The radioactivity and specific activity of the plasma EFA showed no marked change during exercise. When a 3-hr infusion was stopped 5 min before exercise, the radioactivity in the plasma FFA fraction decreased rapidly in the first 10 min of exercise, followed by a very low but constant disappearance rate. The disappearance of radioactivity from the plasma (FFA and EFA combined) during exercise was less than 1% of the C14O2 output. Therefore, it was concluded that the intracellular fat pool plays an important role as an energy source, whereas the plasma EFA did not seem to participate appreciably in the 6-fold elevated metabolism.