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

Objective: To determine the time course and spatial distribution of up take of macromolecules in the small intestine of rats subjected to cut aneous thermal injury. Design: Prospective, controlled animal study. S ubjects: 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 inj ury. 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 i ntestinal 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 tiss ues were fixed with paraformaldehyde and cryosections were examined by laser confocal microscopy. The mesentery was also observed by laser c onfocal microscopy during incubation with the permeability probes. The disappearance of fluorescence was studied after washing the dextran p robes from the gut lumen. Measurements and Main Results: In small inju ries, 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. Co nclusions: 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 her e will be useful to examine intestinal transport in various pathologic situations.