This protocol seeks to define aspects of intestinal and hepatic uptake and metabolism of several amino acids. The major hypothesis to be tested is that the splanchic bed (intestine and liver) conserves essential amino acids and metabolites while synthesizing and metabolizing nonessential amino acids. The aims of the study include defining the relative roles of enteral and hepatic extraction/metabolism in the disposition of glutamate, alanine, methionine and other amino acids. Emphasis will also be placed on studies of the transamination of alpha-ketoisocaproic acid (KIC) to leucine since this reaction is of potential importance in the design of nutritional regimens for patients with renal disease.