Enterocyte functional adaptation following intestinal resection

Following massive small bowel resection, the remaining intestine undergoes compensatory adaptation to maintain absorptive capacity. The purpose of this study was to determine the relative importance of mucosal hyperplasia and functional adaptation by individual enterocytes in this process. Distal ileum was harvested from rats 2 weeks following 70% small bowel resection or transection with reanastomosis. Transport parameters were determined in Ussing chambers. Short-circuit current (I(sc)) responses to additions of 3- O-methylglucose were measured to assess Na⁺/glucose cotransporter kinetics. Microvillus absorptive surface areas were calculated with computer-assisted morphometric modeling. These surface area values were used to normalize transport parameters. Ileal absorptive surface area was 70% greater in resection tissues than in transection tissues (P < 0.05). Na⁺ and Cl fluxes were generally lower in the resection group. Na⁺/glucose cotransporter ΔI(sc)max (an index of cotransporter quantity) for resection and transection tissues were 0.3 ± 0.1 and 1.8 ± 0.3, respectively (P < 0.05). K(m) (an index of cotransporter affinity for substrate) did not differ significantly. Following intestinal resection, ileal surface area increases; however, transport parameters, when normalized to absorptive surface area values, diminish. During early postresection adaptation, expansion of ileal absorptive surface area due to hyperplasia seems to play a greater role than upregulation of enterocyte Na⁺, Cl^-, and glucose absorption.