Muscle Protein Turnover and the Wasting Due to Injury and Disease

It is well recognized that muscle makes a major contribution to amino acid and protein metabolism in the body but many of the details are still obscure. An understanding of the effects of injury and disease on muscle protein turnover and amino acid metabolism requires much more basic information on the mechanisms for the mobilization of amino acids from lean tissue and the relative contributions of different tissues. Several methodological approaches are reviewed. Our current knowledge of the effects of injury and disease on amino acid balance and protein turnover in muscle is als reviewed. It is suggested that the effects may be broadly categorized as those causing rapid increases in protein turnover with breakdown exceeding synthesis, and those in which synthesis is depressed below breakdown. The former response is more likely following severe trauma and during sepsis and the latter more common after moderate injury and during malnutrition. A knowledge of the mechanisms of loss of amino acid from muscle tissue is vital to the design of rational therapeutic intervention.