MORPHOLOGICAL FACTORS INFLUENCING TRANSEPITHELIAL CONDUCTANCE IN A RABBIT MODEL OF ILEITIS

Background and Aims: Infection of rabbits with coccidia (Eimeria magna ) causes chronic ileal inflammation and diarrhea. inflamed ileum also shows decreased transmural conductance. The aim of this study was to c haracterize morphological factors known to affect paracellular permeab ility that may alter transmural conductance in inflamed ileum. Methods : Ileal mucosa was mounted in Ussing chambers for study of [H-3]mannit ol and [H-3]inulin fluxes. Light and electron microscopy were used for morphometric studies. Alterations in the zonula occludens of epitheli al cells were evaluated in freeze-fracture replicas. Results: Inflamed ileum showed diminished paracellular fluxes. Inoculated rabbits showe d marked lymphoplasmocytic infiltration and villus blunting in ileum. Villus linear junctional density was unaffected. However, total villus apical surface area per square centimeter of tissue was reduced in in flamed ileum, causing a diminished total villus linear junctional path way per square centimeter of apical surface. Villus zonula occludens s trand number was reduced in inflamed ileum, whereas the frequency of b oth villus and crypt lateral surface extrajunctional strands increased . Conclusions: Chronic inflammation exerts a profound effect on ileal paracellular permeability. Morphological data suggest that this effect may be caused in part by alterations in inflamed ileal mucosal struct ure and tight junctional organization and density, particularly on vil li.