Rates of small intestinal mucosal protein synthesis in human jejunum and ileum

We investigated possible differences in the rates of mucosal protein synthe sis between the proximal and distal regions of the small intestine. We took advantage of access to the gut mucosa available in otherwise healthy patie nts with ileostomy in whom the terminal ileum was histologically normal. Al l subjects received primed, continuous intravenous infusions of L-[1-C-13]l eucine after an overnight fast. After 4 h of tracer infusion, jejunal biops ies were obtained using a Crosby-Kugler capsule introduced orally; ileal bi opsies were obtained via endoscopy via the ileostomy. Protein synthesis was calculated from protein labeling relative to intracellular leucine enrichm ent obtained by appropriate mass spectrometric measurements. Rates of jejun al and ileal mucosal protein synthesis were significantly different (P < 0. 001) at 2.14 +/- 0.2 and 1.2 +/- 0.2 %/h (means +/- SD). These are lower th an rates in normal healthy duodenum (2.53 +/- 0.25 %/h), suggesting a grada tion of rates of synthesis along the bowel. Together with other data, these results suggest that mucosae of the bowel contribute not more than 10% to whole body protein turnover.