Abstract
Net protein loss and large decreases in plasma glutamine concentration are characteristics of critical illness. We have used [2-
15
N]glutamine and [1-
13
C]leucine to investigate whole body glutamine and leucine kinetics in a group of critically ill patients and matched healthy controls. Glutamine appearance rate (R
a,Gln
) was similar in both groups. However, in the patients, the proportion of R
a,Gln
arising from protein breakdown was higher than in 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 glutamine concentration was 38 ± 5% lower ( P < 0.001) than in the control group. Leucine appearance rate (whole body proteolysis) and nonoxidative leucine disposal (whole body protein synthesis) were 59 ± 14 and 49 ± 15% higher 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). These results demonstrate that critical illness is associated with a major increase in protein turnover. The acute decrease in plasma glutamine concentration and the unaltered plasma R
a,Gln
suggest that the increase in proteolysis is insufficient to meet increased demand for glutamine in this severe catabolic state.