Rationale and objectives: Studies have shown that water-soluble radiographic contrast media may be useful as intestinal permeability probes. The current study was undertaken to provide information about the route by which such a permeability probe crosses the mucosal epithelium.
Materials and methods: The authors administered 3 mL of iodixanol (iodine, 320 mg/mL) by means of an enema into the colons of (a) rats with experimental colitis induced 14 days earlier and (b) normal rats. At various intervals after the enema, laparotomy was performed and the colon was identified and longitudinally split immediately before cryofixation, without prior interruption of circulation. Freeze-dried cryosections were studied by means of electron microscopy and x-ray microanalysis.
Results: Approximately equal concentrations of iodine were found intracellularly and between the epithelial cells of the colonic mucosa. Ninety percent of analyzed cells had a normal sodium-potassium ratio and low levels of intracellular chlorine, indicating intact cell membranes. Nevertheless, many of these cells, in specimens from both normal rats and rats with colitis, contained high intracellular iodine concentrations.
Conclusion: The transcellular route seems to be at least as important as the paracellular route for permeation of the highly water-soluble molecule iodixanol through the mucosal epithelium of both normal and inflamed rat colon. This finding may contradict previous findings in other water-soluble substances.