ENDOGENOUS RENAL TRANSPORT OF FREE AMINO ACIDS IN INFANCY AND CHILDHOOD

Abstract

Endogenous renal transport of free amino acids was determined in 12 infants, between the ages of 16 days and 4 months, and in 12 children, between 2 and 13 years of age. Values of the serum concentrations, urinary excretion, renal clearance rates, net tubular reabsorption, and percentage tubular reabsorption of 17 amino acids were obtained by short-term clearance studies, including the determination of the glomerular filtration rate by inulin. The amino acids were determined by ion exchange chromatography. A comparison of the values of infants and children revealed a specific feature of the kidney function in infancy. The urinary excretion of threonine, serine, proline, glycine, and alanine and the clearance rates of serine, proline, glycine, and alanine were significantly higher in infancy. The percentage tubular reabsorption of all amino acids was characteristically lower in infancy than in childhood, while the values of the net tubular reabsorption related to the glomerular filtration rate (TAA/CIn) were equal in both groups. These findings are thought to be due to a greater degree of heterogeneity of nephrons with increased glomerulotubular imbalance during the period of postnatal kidney development.