Observations on the urinary amino acid excretion in man: the influence of age and diet

Abstract

Using the Dowex 50 column chromatographic technique of Moore and Stein, studies have been made of free amino acid excretion in 12 infants and two older children in order to evaluate the influence of age and of diet. Consideration has been given to various stand ards of reference for evaluating amino acid excretion, and it is concluded that it is best expressed in terms of creatinine excretion. In terms of creatinine excretion it was found that premature infants excrete roughly ten times as much free amino acid as do subjects ten or more years old, and that full-term infants excrete roughly three times as much as the older subjects. Our data on 10-year-olds reveal values virtually identical with those reported for adults. The pattern of individual amino acid excretion was found to differ in early life from that seen in older children and adults. A number of amino acids are present in greater amount and several are found only at that time of life. Hydroxyproline has been identified in the urine of premature and newborn infants. An unidentified ninhydrin reactant, designated as peak No. 9 is described which has not been observed in subjects more than 5 months old. The anomalous behavior of taurine is described, being present in large quantities in the neonatal period, virtually disappearing thereafter, and reappearing again in quantity by the tenth year. Certain late effects of prematurity are described. The effects of diet on amino aciduria are considered, the indications being that the amino acid output in the urine is influenced to some extent by the diet. Comparisons were made of free amino aciduria on a diet of whole protein (milk) and on a synthetic diet supplying nitrogen as a mixture of natural amino acids. Certain differences were encountered the significance of which is discussed. The disappearance of peak No. 9 on the amino acid diet was particularly striking. Some preliminary attempts to identify it are reported.