The metabolic consequences of critical illness: acute effects on glutamineand protein metabolism

Net protein loss and large decreases in plasma glutamine concentration are characteristics of critical illness. We have used [2-N-15]glutamine and [1- C-13]leucine to investigate whole body glutamine and leucine kinetics in a group of critically ill patients and matched healthy controls. Glutamine ap pearance rate (Ra,Gln) was similar in both groups. However, in the patients , the proportion of Ra,Gln arising from protein breakdown was higher than i n the control group (43 +/- 3 vs. 32 +/- 2%, P < 0.05). Glutamine metabolic clearance rate (MCR) was 92 +/- 8% higher (P < 0.001), whereas plasma glut amine concentration was 38 +/- 5% lower (P < 0.001) than in the control gro up. Leucine appearance rate (whole body proteolysis) and nonoxidative leuci ne disposal (whole body protein synthesis) were 59 +/- 14 and 49 +/- 15% hi gher in the patients (P < 0.001). Leucine oxidation and MCR were increased in the patients by 104 +/- 37 and 129 +/- 39%, respectively (P < 0.05). The se results demonstrate that critical illness is associated with a major inc rease in protein turnover. The acute decrease in plasma glutamine concentra tion and the unaltered plasma R-a,R-Gln suggest that the increase in proteo lysis is insufficient to meet increased demand for glutamine in this severe catabolic state.