THE QUANTITATIVELY MINOR ROLE OF CARBOHYDRATE IN OXIDATIVE METABOLISM BY SKELETAL MUSCLE IN INTACT MAN IN THE BASAL STATE. MEASUREMENTS OF OXYGEN AND GLUCOSE UPTAKE AND CARBON DIOXIDE AND LACTATE PRODUCTION IN THE FOREARM 12

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Abstract
Metabolism of the forearm, a mass of tissue which is predominantly skeletal muscle, was studied in 14 normal men in the basal state by measuring simultaneously differences in arterial and venous concentrations of O2, CO2 glucose and lactate. In 8 subjects blood flow through the segment was measured also and rates of uptake of O2 and of glucose and of production of CO2 and lactate were determined. O2 consumption by resting muscles of the forearm is vigorous. If it is representative of O2 uptake by all skeletal muscles, then muscle accounts for 35 to 40% of total body O2 uptake at rest and following a 16-hour fast. In contrast, muscle glucose uptake is relatively small. By a similar extrapolation, muscle accounts for only 20% of total body glucose uptake. Without exception, venous lactate concentration exceeded arterial; muscle produced lactate continuously even at rest and in the presence of active O2 consumption On the average, 60% of glucose uptake by forearm muscles was accounted for by lactate production, with wide individual variation. The remaining glucose, not accounted for by lactate production, was assumed to be oxidized completely. Its oxida- tion could account for only 7% of the O2 uptake; that is, glucose abstracted from blood is only a minor fuel for skeletal muscle under these conditions. The mean R.Q. of forearm muscle was 0.80, suggesting that the major non-carbohydrate material which serves as the substrate for oxidation in forearm muscle is Upid.