Effect of deoxycholate on the perfused rat colon. Scanning and transmission electron microscopic study of the morphological alterations occurring during the secretagogue action of deoxycholate.

In parallel with the study on the correlation between increased mucosal permeability and the secretagogue effect of deoxycholate on the perfused rat colon, we examined the mucosal morphology by scanning and transmission electron microscopy. Dependent on concentration (2, 4, and 8 mmol/l), the treated mucosa showed structurally altered 'ballooned' absorptive cells, severely injured sloughing cells, and exfoliated cells lying on the surface. In spite of these changes, the continuity of the epithelial lining was maintained. Patchy defects exposing the lamina densa of the basement membrane could be observed only in specimens artificially altered by cell loss through vigorous rinsing. Clusters of extruded cells were still seen attached to the mucosal surface in the region between the openings of neighbouring crypts when net transfer of fluid and permeability after a period of recovery had returned to control levels. These findings support the hypothesis that fluid filtration during perfusion with deoxycholate occurs via a paracellular pathway through a leaky, damaged epithelium.