Effect of exercise on the tissue respiration of the brain,skeletal muscle,heart, liver,kidneys, and spleen

Summary The effects of a single sustained physical exercise on the respiration of various tissues of rats were investigated with the aid of Warburg's method. The animals were made to run on a treadmill for 90 min, i.e., until distinct signs of fatigue. The oxygen uptake of skeletal muscles was increased, and that of brain and kidneys reduced, both by a statistically significant margin. Changes in the respiration of liver, heart, and spleen were not statistically significant.The authors attribute increased respiration of skeletal muscles during physical exercise to intensified carbohydrate metabolism in muscle and the concomitant increase in the activity of the oxidative systems of muscle.The observed inhibition by severe physical exercise of the oxygen uptake of brain may have been caused by the inhibitory effects of serotonin and, possibly, corticosteroids, or still other active substances whose level rises in the organism of a tired animal.Oxygen uptake in the kidneys was probably reduced by an adaptive lowering of the activity of that organ's respiratory enzymes, which was the result of a markedly diminished renal blood supply during physical effort.