STUDIES ON AMINO ACID EXCRETION IN MAN. III. AMINO ACID LEVELS IN PLASMA AND URINE OF NORMAL MEN FED DIETS OF VARYING PROTEIN CONTENT 1

Abstract

The amino acids, methionine, lysine, arginine, histidine, leucine, isoleucine, valine and threonine were measured microbiologically in the food, plasma and urine of 2 normal adult men fed a variety of diets. The fasting free, combined, and protein amino acid content of plasma, in general, did not fluctuate significantly despite considerable variation in the quantity of amino acids ingested in the food. The output of amino acids in the urine was small, avg. 2.5% of the intake. Excretion of 6 of the 8 amino acids was relatively constant despite considerable variation in intake. The outputs of histidine and threonine fluctuated slightly in relation to the varying intakes. The addition of crystalline DL-methionine to a diet adequate in this amino acid was accompanied by increases in whole plasma levels of methionine and of free and combined non-precipitable (tungstic acid) methionine and lysine. The urinary output of methionine increased slightly; no significant changes occurred in the excretion of the other amino acids. In one subject the oral admn. of a peptone soln. treated with H2O2 and containing markedly reduced quantities of 7 of the 8 amino acids studied was accompanied by definite decreases in the free levels of these amino acids. During the same periods, the amino acid outputs in the urine increased considerably.