Intramuscular energy sources in exercising normal and pancreatectomized dogs

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Abstract
In dogs with indwelling arterial and venous catheters, the FFA [free fatty acid] turnover was reduced by nicotinic acid (90-110 mg/kg iv or ia). Then they ran on a treadmill for 2-3 hr. Palmitate-1-C14, glucose-U-C14 or DL-[beta]-hydroxybutyrate-3-Cl4 was infused at a constant rate. The rate of oxidation of plasma FFA or that of plasma glucose was measured, respectively. The contribution of [beta]-hydroxy-butyrate to the CO2 output proved to be negligible. The amount of O2 required for and CO2 derived from the oxidation of FFA and glucose was substracted from the total O2 uptake and CO2 output and the resulting RQ [respiratory quotient] was considered as intramuscular RQ. In normal dogs this proved to be 0.87 [plus or minus] 0.004 and in the diabetic animals 0.77 [plus or minus] 0.015. The difference was significant (P< .001). It was estimated that in normal dogs in 2 hr. 1 g of muscle oxidized about 5 umoles fatty acids from intramuscular depots which required about 22% of the total O2 uptake. The corresponding figures for diabetic dogs were 11.7 umoles/g per 2 hr. or 47.8% of O2 consumption. Fat stored in the muscle can serve as an energy source and in pancreac-tectomized dogs it is the major intramuscular substrate for the oxi-dative work metabolism.