STUDIES IN THE METABOLISM OF MUSCLE

Abstract

The respiratory quotient of exercising mammalian muscle as determined by quantitation of the gases in the blood in the vessels of the active parts was compared with the respiratory quotients of the whole body during rest and exercise as determined by analysis of the expired air. Forty-nine experiments were performed on 30 decerebrate dogs. The experiments fall into 2 major groups, one on dogs fasted from 5 to 15 days and another on dogs fed a diet containing considerable carbohydrate. In certain animals in each group the venous blood was drawn directly from the femoral vein, i.e., blood returning from the whole lower extremity, and in others the venous blood was drawn after the circulation of the gastrocnemius and flexor digitorum sublimis muscles had been isolated. The averages of the various R. Qs were as follows: directly from the blood of the non-isolated muscles of the lower extremity of fasted dogs: 0.81 [plus or minus]0.05 during exercise, and for the expired air 0.81 [plus or minus] 0.03 on the resting animals, and 0.83+0.05 on the exercising animals; for the isolated muscles of fasted dogs: 0.78 + 0.06 during exercise, and 0.80 [plus or minus]0.03 and 0.96+0.07 for the resting and working intact animals respectively; for the muscles of the lower extremity of fed dogs: 0.91 [plus or minus]0.04 during exercise and 0.90 +0.02 on resting dogs and 0.95 + 0.02 on working dogs, and finally for the isolated muscles of fed dogs: 0.98 [plus or minus]0.07 during exercise and 0.94 [plus or minus] 0.02 and 1.06 [plus or minus]0.10 for the resting and working animals respectively. In view of the close agreement between the R. Qs at rest and those in exercise, it is concluded that exercising muscle from the 2nd to the 15th minute of exercise utilizes foodstuffs in approximately the same proportions as the whole body during rest.