TRANSPORT OF FLUORESCENT DEXTRANS ACROSS THE RAT ILEUM AFTER CUTANEOUS THERMAL-INJURY

Objective: To determine the time course and spatial distribution of uptake of macromolecules in the small intestine of rats subjected to cutaneous thermal injury. Design: Prospective, controlled animal study. Subjects: Fifty-five female Sprague-Dawley (CD) rats subjected to scald burn injury covering 20% (small injury; n = 29) and 40% (large injury; n = 6) of the total body surface area between 3 and 72 hrs after injury. Animals subjected to sham injury (n = 20) were used as controls. Interventions: The intestine was cannulated near the distal ileum and incised 7 cm upstream. After perfusion with physiologic buffer, this intestinal loop was filled with the same buffer containing fluorescent-labeled dextrans (3 and 70 kilodaltons molecular weight) and Ligated 4 cm from the injection point. After a 2-hr incubation period, the tissues were fixed with paraformaldehyde and cryosections were examined by laser confocal microscopy. The mesentery was also observed by laser confocal microscopy during incubation with the permeability probes. The disappearance of fluorescence was studied after washing the dextran probes from the gut lumen. Measurements and Main Results: In small injuries, there was a transient uptake of the Q-kilodalton dextran by the epithelium in focal regions of the ileum with the effects seen between 7 and 21 hrs after injury. In large injuries, epithelial staining was visible within 3 hrs, and the marker was seen to translocate both to the lymphatics and the blood vessels of the mesentery. In comparison, the 70-kilodalton dextran was visible within the intercellular spaces. Little or no epithelial staining was seen in sham-injured animals. Conclusions: These results suggest that a transcellular pathway for the translocation of small macromolecules from the lumen to the mesentery can be activated after burn injury. The novel techniques described here will be useful to examine intestinal transport in various pathologic situations.