Effects of glutamine and recombinant human growth hormone on protein metabolism in prepubertal children with cystic fibrosis

To determine whether recombinant human GH (rhGH) and glutamine (GLN), alone or in combination, have a protein anabolic effect and whether rhGH alters GLN kinetics in cystic fibrosis (CF), nine 9.6 +/- 0.5-yr-old children with CF who were either undernourished (weight/height, <50th percentile) or short (height, <5th percentile) received 2-h infusions of [(13)C]bicarbonate (to assess CO(2) production), followed by 4-h infusions of [(13)C]leucine and [(15)N]GLN, on 4 separate days in the postabsorptive state: 1) at baseline, and after a 4-wk treatment with 2) oral GLN (0.7 g/kg.d), 3) rhGH (0.3 mg/kg.wk), and 4) GLN and rhGH combined (GLN and rhGH regimens were in randomized order). No significant effect of GLN on leucine kinetics was detectable. In contrast, rhGH induced a 32% reduction in leucine oxidation and a 13% stimulation of nonoxidative leucine disposal, an index of protein synthesis (P < 0.05), with no change in proteolysis or GLN kinetics. The combined GLN plus rhGH regimen had similar effects as rhGH alone. We conclude that in children with CF, 1) oral GLN may not promote protein gain in the fasting state; and 2) a short course of rhGH has a potent anabolic effect that is mediated by stimulation of protein synthesis and does not affect GLN kinetics.