Exacerbation of intestinal permeability in rats after a two-hit injury:: Burn and Enterococcus faecalis infection

Objective: To determine alterations in intestinal epithelia[ permeability to solutes in burn injured rats with and without Enterococcus faecalis infection and the role of neutrophils in the intestinal permeability changes. Design: Prospective sham-controlled animal study. Setting: University research laboratory. Subjects. Male Sprague-Dawley rats. Interventions: Rats were subjected to 30% total body surface burn (B group), E faecalis infection (EF group) induced via intraabdominal implantation of bacterial pellet, or combination of burn injury and E. faecalis infection (B+EF group). Measurements and Main Results: In vivo measurements of intestinal permeability were carried out after intraluminal injection of H-3 lactulose and C-14 mannitol in the ileum of sham, B, EF, and B+EF groups of rats, 1 and 2 days after injury. Lactulose permeability was increased in the injured rat groups (B, EF, B+EF) on day 1 postinjury compared with sham. The combined injury group (B+EF) had the highest level of lactulose permeability. Although a significant change in lactulose permeability from day 1 to day 2 postinjury could not be demonstrated in the B and EF groups, lactulose permeability in the B+EF group on day 2 postinjury markedly decreased from day 1 but was still significantly higher than that in the sham group. Mannitol permeability was increased in all injured rat groups on day 1 postinjury; on day 2 it remained elevated post-B, decreased post-EF, and further increased after B+EF. Ex vivo measurements of lactulose movements across intestinal epithelial monolayers (IEC-18) were carried out in the presence of blood neutrophils from sham, B, EF, or B+EF rats. We also measured ex vivo transepithelial migration of neutrophils from sham, B, EF, or B+EF rat groups. Neither the transepithelial lactulose movement in the presence of neutrophils from, nor neutrophil migration in, the B or EF rats was significantly different from sham. However, a significant increase in transepithelial lactulose movement and neutrophil migration occurred in the B+EF group. Immunoblot analyses and in situ histochemical localizations of intestinal tight junction proteins, occludin and claudin-3, showed decreases in the distribution of occludin but not claudin-3 in the B, EF, and B+EF groups. Conclusions: Alterations in intestinal solute permeability and disruption of tight junction integrity after a two-hit injury with burn and E. faecalis infection, but not after individual injuries of burn or E. faecalis infection, are likely associated with heightened neutrophil flux across the intestinal epithelium.