INCREASED PERMEABILITY OCCURS IN RAT ILEUM FOLLOWING INDUCTION OF PANCOLITIS

Acetic acid-induced pan colitis in rats leads not only to colonic inju ry but also to a bystander ileal injury, characterized by decreased fl uid and electrolyte absorption without associated histological injury or infiltration of inflammatory cells. To examine the nature of this d ecreased ileal fluid and electrolyte absorption, we measured effect of acetic acid-induced pancolitis on ileal transmural sodium and chlorid e transport, as well as on ileal permeability to mannitol and inulin o n mucosal sheets mounted in Ussing chambers. In addition, ileal tight junctional morphology was assessed by electron microscopy. In colitic animals, ileal serosal-to-mucosal sodium and chloride transmural fluxe s were increased (P < 0.05); compatible with the observed decrease in net fluid absorption. Mannitol and inulin ileal serosal-to-mucosal and mucosal-to-serosal ileal fluxes were similarly increased (P < 0.05), suggesting that an increase in ileal permeability occurred during acet ic acid-induced pancolitis. This increase in ileal permeability was no t accompanied by changes in tight junctional ultrastructure. These res ults suggest that: (1) the decrease in ileal fluid and electrolyte abs orption seen during acetic acid-induced rat pancolitis occurred in par allel with a rise in both transcellular and paracellular permeability, and (2) the ileal permeability changes were not accompanied by struct ural changes.