Chronic sepsis is always associated with profound muscle wasting. The net catabolism may be due to a decreased skeletal muscle protein synthesis, increased degradation, or combination of both. Knowledge of which pathway is altered is fundamental to the con- tinued development of rational and specific therapies to attenuate the loss of skeletal muscle protein. In our chronic septic animal model, preliminary studies in vivo have demonstrated a 50% reduction in the rate of skeletal muscle protein synthesis. Protein synthesis may be regulated by 1) decreased availability of amino acids, ATP and GTP as substrates; 2) altered availability of ribosomes, tRNA, mRNA and enzymes which catalyze peptide-bond formation; and/or 3) altered activity of factors affecting rates of peptide chain initiation, elongation or termination. The proposed research will determine the physiologic significance of the septic-induced effects on each of these mechanisms in restricting protein synthesis. The chronic 15 days) septic rat model will be induced by creating a stable intra-abdominal abscess using an E. coli+B. fragilis infected sterile fecal-agar pellet as the foreign body nidus. Rates of protein synthesis in control, sterile inflammatory, and chronic septic rats will be determined in vivo and in vitro perfused hemicorpus by measuring the incorporation of (3H)-phenylalanine into protein, using the phenylalanyl-tRNA specific radioactivity as the precursor pool for estimating rates of protein synthesis. Tissue metabolites, amino acids, RNA, and ribosomal subunits will be measured to determine which mechanisms prevail in sepsis. Decreased synthetic rates in sepsis were not due to either an energy deficit as tissue high energy phosphate (ATP+CrP) and the ATP/ADP ratio were not altered, or a decreased capacity for protein synthesis, as the total tissue RNA content was not altered in sepsis. However, the translational efficiency was significantly reduced in skeletal muscle from septic animals. The molecular mechanisms involved in the decreased translational efficiency in sepsis will be determined by measuring the levels of 60s and 40s ribosomal subunits. In addition, the rate of protein degradation will be determined in vitro by the release of phenylalanine under conditions where the reutilization of phenylalanine is inhibited by cycloheximide. The role of interleukin-l in enhancing lysosomal proteases will be determined. Pharmacological modulation of protein turnover will be assessed by determining the role of hormones (insulin, cortisol) and amino acids (BCAA, glutamine) in reversing septic-induced changes.
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