Effect of Source of Dietary Nitrogen on Plasma Concentration and Urinary Excretion of Amino Acids of Men

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Abstract
The postprandial plasma concentration of most essential and nonessential amino acids decreased or remained at fasting values when the major portion of the daily intake of 6.28 g N was provided by casein. When a mixture of 18 amino acids simulating casein was given, the postprandial plasma concentration of both essential and nonessential amino acids increased during the first hour but decreased during the second hour to values somewhat above the fasting ones. When the nonessential nitrogen was furnished by glycine and diammonium citrate or by glycine, diammonium citrate and glutamic acid, the plasma concentration of individual essential amino acids increased by the first hour and during the second hour remained elevated or continued to increase. The fasting and postprandial concentrations of histidine and proline were much lower and that of arginine somewhat lower when these amino acids were excluded from the diet. Glycine in fasting and postprandial plasma and in urine increased significantly when this amino acid furnished one-half or one–third of the nonessential nitrogen. The concentration of threonine in fasting plasma and the amounts of threonine, serine and taurine excreted were significantly increased when large amounts of glycine or diammonium citrate were given.