Role of extramuscular energy sources in the metabolism of the exercising dog.

Abstract

Trained and untrained dogs with indwelling arterial and venous catheters ran on a treadmill on various slopes (0-15%) at a speed of 100 m/min for various lengths of time (1/2-5 hr). Albumin-bound palmitate-1-14C or glucose-14C (U) was infused intravenously at a constant rate. O2 uptake, CO2 output, and the specific activities of CO2, of plasma FFA [free fatty acids], or that of glucose were measured. The rates of removal and oxidation of FFA were calculated from the specific activity of plasma FFA and plotted against the plasma FFA level. The obtained regression equations were used to estimate rates of oxidation and uptake of FFA in experiments with radioglucose. In short heavy exercise, plasma FFA supplied 20-30% of the energy expenditure, while in prolonged work 70-90% of the energy derived from this source. In either case oxidation of plasma glucose played only a minor role and contributed not more than 10-15% to the caloric expenditure. It was concluded that the effectiveness of substrate supply via blood circulation depends much more on the rate of release of FFA from the adipose tissue than on hepatic sugar output.