The metabolic regulation of amino acids and its inter-organ integration, particularly of the so-called conditionally indispensable amino acids, is profoundly altered in severe burn injury. This project involves integrated studies in burn patients, healthy human subjects, and an experimental model of burn injury designed (I) to quantify the in vivo alterations in the metabolic "triangle" by glutamine, proline, and arginine; (ii) identify underlying metabolic and cellular events responsible for the perturbations (iii) design and test metabolic/nutritional interventions constructed to produce a more effective maintenance of amino acid homeostasis and, in turn, host defense and wound healing. Our working hypothesis is that the enhanced proteolysis, particularly in peripheral tissues (skeletal muscle), designed to provide substrate (amino acids) for the liver to support metabolism and function by redistribution of amino acids exceeds the body's ability to efficiently utilize them, contributing to a general "catabolic" state, and cellular depletion. We will measure (1) whole body kinetics of proline, following nutritional modulation via amino acid mixtures, and extend the data through related studies in healthy adult subjects. (2) determine the dynamic status of arginine, citrulline and urea metabolism, using novel mixtures of multiple stable isotope tracers of these amino acids. (3) determine the whole body kinetics of leucine, glutamine and glutamate as affected by burn injury and modulated by glutamine supplementation. Complimentary cellular studies will be carried out, using a burned rat model, to: (1) determine plasma and liver concentrations of these amino acids after burn injury; (2) characterize changes in hepatic amino acid uptake after burn injury and correlate these with hepatic glucose production, acute phase protein synthesis and glutathione metabolism using both in vivo and in vitro models; (3) investigate the regulation of these metabolic pathways by mediators of the inflammatory injury response; (4) study the impact of nutritional formulations enriched with arginine, glutamine, and/or proline on hepatic uptake and metabolism of these amino acids and on hepatic function and damage in the burned rat. This research is expected to significantly expand our understanding of the metabolic basis for burn- induced alterations in amino acid-related changed in energy and nitrogen metabolism and how these might best be attenuated, or enhanced, through "designer" nutritional/pharmacological therapy.