Glutamine Appearance Rate in Plasma Is Not Increased after Gastrointestinal Surgery in Humans

The metabolic response to surgical stress is characterized by muscle protein breakdown and mobilization of amino acids and has been postulated to furnish glutamine and other amino acids to the immune system, gut and liver. The present study was undertaken to investigate whether the whole body appearance rate (Ra)3 of glutamine in plasma is increased after major elective surgery. Fourteen patients (8 males, 6 females) were measured prior to laparotomy and on the second postoperative day. Patients received a primed continuous 6-h infusion of L-[5-15 N]glutamine and L-[1-13C]leucine, and arterial blood samples and muscle biopsies were taken for concentration and enrichment measurements. As expected, the metabolic response to surgery was characterized by a rise in whole body protein breakdown (n = 14, P < 0.001) and a decreased concentration of glutamine in plasma (n = 14, P < 0.001) and muscle (n = 8, P < 0.01). However, these catabolic changes were not reflected by an increase in the plasma Ra of glutamine: 246 ± 8 μmol · kg−1 · h−1 before surgery vs. 241 ± 10 μmol · kg−1 · h−1 on the second postoperative day. We conclude that the whole body Ra of glutamine in plasma is not increased 2 d after elective gastrointestinal surgery. Further studies are warranted to establish whether the lack of an increase in plasma glutamine Ra provides a rationale for glutamine supplementation.