Studies on amino acid excretion in man; amino acids in urine.

Recent interest in the r81e of proteins in gastrointestinal disease has prompted an investigation of certain aspects of this problem. Studies by Cannon and coworkers suggested to us that measurements of the intake and excretion of individual amino acids might supply more complete and significant data than the conventional nitrogen balances alone (1). Hence, in addition to the nitrogen balance, measurements were made of the intake (in food), level in the blood, and excretion in urine of eight amino acids; namely, leucine, isoleucine, valine, threonine, arginine, histidine, lysine, and methionine. The purpose of this paper is to describe the results of typical studies in two healthy, adult men on normal diets and also the adaptation of the microbiological technique utilized in this investigation for the amino acid analysis of urine. Studies on the excretion of amino acids in feces will be reported in a subsequent paper. The data presented in this report indicate (a) that the subjects of this study excreted in the urine a quantity of microbiologically available amino acids equal to 2.46 per cent of the amount ingested, and (b) that the renal tubules selectively reabsorb amino acids.