Glutamine metabolism in Crohn's disease: a stable isotope study

Aims: To determine whether chronic intestinal inflammation alters glutamine utilization, six 31± 6 yr-old patients with Crohn's disease and an age-matched group of 6 healthy subjects received 7-h intravenous infusions of l-[5,5,5- 2H 3]leucine, along with an infusion of l-[1- 13C]glutamine delivered intravenously for the first 3.5 h, and via a nasogastric tube for the subsequent 3.5 hrs. None of the patients was receiving any nutritional supplement or antiinflammatory drug. All were in remission (Crohn's disease activity index < 150) and in a near-normal nutritional status. Methods: We used plasma 2H 3-α-ketoisocaproate to determine leucine appearance rate (Ra), and plasma 13C-glutamine and breath 13CO 2 to determine glutamine Ra and oxidation, respectively. The fraction of enteral glutamine undergoing uptake in the splanchnic bed was determined from the difference in plasma 13C-glutamine enrichments between the intravenous and nasogastric 13C-glutamine infusion periods. Results: Neither leucine Ra, nor plasma glutamine concentration (526±40 vs. 530±50 μmol/l), glutamine Ra (364±19 vs. 355±24 μmol kg −1 h −1), or splanchnic glutamine uptake (61±5 vs. 65±2%) differed between groups. In both groups, glutamine oxidation rose when the glutamine tracer was supplied enterally, compared with the intravenous route (70±6 vs. 39±2% in patients; 69±2 vs. 38±1% in controls), but did not differ between groups. Conclusion: When in remission, patients with Crohn's disease have normal rates of proteolysis, and glutamine production, utilization, oxidation, and splanchnic uptake. The data suggest there is no obvious requirement for glutamine in patients with quiescent Crohn's disease.