Effects of glutamine supplementation, GH, and IGF-I on glutamine metabolism in critically ill patients

During critical illness glutamine deficiency may develop. Glutamine supplementation can restore plasma concentration to normal, but the effect on glutamine metabolism is unknown . The use of growth hormone (GH) and insulin-like growth factor I (IGF-I) to prevent protein catabolism in these patients may exacerbate the glutamine deficiency. We have investigated, in critically ill patients, the effects of 72 h of treatment with standard parenteral nutrition (TPN; n = 6), TPN supplemented with glutamine (TPNGLN; 0.4 g.kg(-1).day(-1), n = 6), or TPNGLN with combined GH (0.2 IU.kg(-1).day(-1)) and IGF-I(160 mu g.kg (-1).day(-1)) (TPNGLN+GH/IGF-I; n = 5) on glutamine metabolism using [2-N-15]glutamine. In patients receiving TPNGLN and TPNGLN+GH/IGF-I, plasma glutamine concentration was increased (338 +/- 22 vs. 461 +/- 24 mu mol/l, P < 0.001, and 307 +/- 65 vs. 524 +/- 71 mu mol/l, P < 0.05, respectively) and glutamine uptake was increased (5.2 +/- 0.5 vs. 7.4 +/- 0.7 mu mol.kg(-1).min(-1), P < 0.05 and 5.2 +/- 1.1 vs. 7.6 +/- 0.8 mu mol.kg(-1).min(-1), P < 0.05). Glutamine production and metabolic clearance rates were not altered by the three treatments. These results suggest that there is an increased requirement for glutamine in critically ill patients. Combined GH/IGF-I treatment with TPNGLN did not have adverse effects on glutamine metabolism.