Exudative and absorptive permeability in different phases of an experimental colitis condition

Increased intestinal 'permeability' in inflammatory bowel disease and in animal models of this disease has been reported. This study asks if permeability changes are bidirectional and parallel cellular inflammation.

In rats acute inflammatory cell infiltration (ICI) was induced in an excluded bowel loop by instillation of 4% acetic acid. Plasma exudation was investigated by intravenous infusion of 125I-albumin and determination of radioactivity in loop perfusates. Absorption was measured by placing 51Cr-ethylenediaminetetraacetic acid in the loop and counting total radioactivity appearing in urine over 24 h.

Acute ICI was induced with acetic acid on day 4 but, as judged by ICI and histology, recovered by day 14. Acetic acid treatment resulted in increased absorption on day 4, which return to control levels by day 14. Acetic acid treatment resulted in increased plasma exudation on day 4, which remained increased on day 14.

Absorption and exudation changes are not necessarily bidirectional, and ICI may not be required for significant and sustained plasma exudation to take place. We suggest that the exudative response reflects a 'functional inflammation' that may occur and be important also in the absence of the traditional indices of bowel inflammation.