Extrinsic neural innervation mediates absorption of water and electrolytes in canine proximal colon in vivo

Introduction. Extrinsic innervation mediates a pro-absorptive effect in small intestine. Our aim was to determine whether extrinsic neural input modulates similar effects in the proximal colon in vivo. Methods. Ten adult dogs underwent enteric isolation of a 50-cm proximal colon loop; five each were randomized to undergo extrinsic denervation (Ext Den) of the isolated colonic segment or to serve as neurally innervated controls. After recovery, a 38°C electrolyte solution (Na⁺ 125 meq/L, K⁺ 9 meq/L, C^- 75 meq/L, HC0₃^- 65 meq/L) was infused at 4 ml/min into the segment. Effluent was collected in 30-min intervals for 2 h after achieving steady state (determined by ¹⁴C nonabsorbable marker recovery); four studies were conducted at 1 and 12 weeks postoperatively. Net flux of H₂0, Na⁺, K¹, and Cl^- was determined. Colon morphometry was evaluated at 0 and 14 weeks. Data are presented as x̄ ± SEM. Unpaired t test was applied for comparisons. Results. Net absorptive flux of H₂0 (μL/min/cm) was decreased in Ext Den vs controls at 1 week (4.40 ± 0.63 vs 7.92 ± 0.92, P 5 0.03) but was not different at 12 weeks (4.70 ± 1.20 vs 5.97 ± 0.69; P > 0.05). Na⁺ and C^- followed the trends in H₂0 absorption (P ≤ 0.05). Crypt depth (μm) decreased in controls at 14 weeks vs 0 week (915 ± 20 vs 740 ± 07, P = 0.01) but remained unchanged in Ext Den. Conclusions. Loss of extrinsic neural input decreases colonic absorption. This observation suggests that extrinsic neural innervation provides net proabsorptive mechanisms for absorption of water and electrolytes in the proximal canine colon.