Decreasing “Amino Acid Hunger” of Human Muscle with Age. ∗

Abstract

Summary

1. Injected C₁ ¹¹α-aminoisobutyric acid was much more strongly concentrated by skeletal muscle in children than in men. The greater general uptake by tissues could be recognized by the resultant consistently lower plasma level in the young. 2. The absence of catabolism of this amino acid was shown by observation of less than 0.002% of the injected C¹⁴ in expired air during 6 hours, counting respiratory CO₂ in the form of Li₂CO₃. After 24 hours average concentration in the body water was about 4 times that in the plasma water. A renal clearance of 56 ml of plasma per min was observed.