Determination of protein synthesis in human ileum in situ by continuous [1-13C]leucine infusion

1 Department of Surgery, Klinikum Grosshadern, Marchioninistr. 15, D-81377 Munich, Germany; and 2 Department of Pediatrics, Dr. v. Haunersches Kinderspital, Ludwig-Maximilian University, 80337 Munich, Germany Efficient protein synthesis plays an important role in the physiology and pathophysiology of the human gastrointestinal tract. Because of methodological restrictions, no studies on ileal protein synthesis in situ are available in humans. We used advanced mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) to determine directly the incorporation rate of [1- 13 C]leucine into ileal mucosal protein in control subjects and postoperative patients. All subjects had an ileostomy, which allowed easy access to the ileal mucosa. To examine changes in ileal protein synthesis during prolonged isotope infusion (0.16 µmol · kg 1 · min 1 , 9.6 µmol/kg prime), studies were performed over a 10-h period. Mucosal biopsies were performed after 3, 6, and 10 h of infusion. Protein synthesis was calculated separately between hour 3 and hour 6 ( period 1 ) and hour 6 and hour 10 ( period 2 ). Control subjects demonstrated an ileal protein fractional synthetic rate of 0.62 ± 0.06%/h in period 1 and of 0.52 ± 0.08%/h in period 2 (not significant). In postsurgical subjects, ileal protein synthesis was significantly higher (1.11 ± 0.14%/h in period 1 , P