INTESTINAL PROTEIN METABOLISM IN SEPSIS

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Protein synthesis is an important function of the intestine, both from a quantitative and qualitative standpoint. The aim of this project is to determine the effect of sepsis on intestinal protein metabolism, synthesis and release of gut peptides, and enterocyte proliferation and migration rates. We will also test the hypothesis that TNF, IL-1 and IL-6 regulate intestinal protein metabolism during sepsis. Finally, we will study the effect of glutamine on protein synthesis in isolated enterocytes from control and septic rats. Sepsis is induced in rats by cecal ligation and puncture (CLP); controls are sham-operated. Protein synthesis rate is measured in vivo in jejunal and ileal mucosa and serosa using a flooding dose of 14C-leucine. In other experiments, protein turnover rates are determined in isolated enterocytes from control and septic rats. Because changes in intestinal protein turnover may reflect altered cellular protein metabolism and or altered cell proliferation rates, cell proliferation is studied by determining incorporation of radioactivity into DNA and by performing autoradiographic studies following the administration of 3H- thymidine (1 mu-Ci/g b.w.). The effect of sepsis on gut hormone synthesis and release is determined by measuring plasma levels of vasoactive intestinal peptide (VIP), peptide YY (PYY), secretion and gastrin in control and septic rats, synthesis of VIP and PYY by isolated enterocytes, and mRNA levels for VIP and PYY in intestinal wall. The role of TNF, IL-1 and IL-6 is elucidated by plasma and tissue (intestinal wall) levels of the cytokines in the septic model and by administering the cytokines (100 mu- g/kg bw i.p. in three repeated does over 16 h) to normal rats followed by measurement of intestinal protein turnover rates. The effect of cytokine antisera administered 2 h before induction of sepsis on intestinal protein synthesis rate will also be tested. Finally, the effect of glutamine on protein synthesis is tested by incubating isolated enterocytes with different concentrations (up to 3.4 micro M) of the amino acid. The effect of glutamine is compared to that of acetoacetate and 3-hydroxybutyrate to test the hypothesis that any effect of glutamine on enterocyte protein synthesis is caused by energy provision. The proposed studies are important because changes in intestinal protein metabolism during sepsis may greatly influence total body protein economy and may also be related to changes in other intestinal functions during sepsis and critical illness.