Regional variation in small intestinal (SI) mucosal protein synthesis and the effect of colectomy on whole-body protein turnover

AIM: We have measured protein synthesis in the SI mucosa to assess possible differences in the rates of mucosal protein synthesis between the proximal and distal regions of the SI in ileostomates and to assess the effect of colectomy on protein turnover. METHODS: Six subjects with ileostomy were studied (mean _+ SD) (46 _+ 21y, 65 _+ 14kg, 169 + 6cm) and the results compared with 8 normal volunteer subjects (44_+15y, 71_+ 12kg, 171 _+ 1 lcm). The ileostomy in these subjects allowed practical access to the distal region of the SI. The terminal ileum was histologically normal in all ileostomy subjects studied. All subjects received primed, continuous IV infusions of L-[1-13C] leucine after an overnight fast. After 4h of tracer infusion jejunal and ileal biopsies were obtained. RESULTS: The results are presented as means _+ SD. Rates of jejunal and ileal mucosal protein synthesis were 2.14 _+ 0.2 and 1.2 + 0.2 (%h -l) respectively; jejunal vs. ileal p<0.001. The whole-body protein turnover rate was, ileostomates vs controls; 145 _+ 15vs. 196 + 44umol/kg/h, p<0.01. In the SI mucosa of subjects with ileostomy the rates of protein synthesis were different at different levels, being significantly higher at the proximal level and lower at the distal level. The plasma leucine enrichment increased by 28% and plasma ketoisocaproate enrichment by 26% with a significantly reduced whole-body protein turnover. CONCLUSION: These changes are probably related to the reduction in the size of the plasma amino acid compartment or reduced lean tissue mass following colectomy and indicate that the colon has a significant contribution to the whole-body protein turnover.