Early effect of low-dose endotoxin on rat cecal mucosa ex vivo

It has been suggested that endotoxin triggers translocation of intestinal bacteria in vivo, either by directly damaging intestinal mucosa or by inducing a systemic inflammatory reaction that leads to mucosal disruption. To address this issue, we examined the immediate effect of extraluminal endotoxin on structure and function of isolated rat cecal mucosa without other inflammatory cells in vitro. The cecal mucosa of 12 male Wistar rats was mounted in modified Ussing chambers filled with Dulbecco's modified Eagle's medium and the ampicillin-resistant Escherichia coli HB101:K12 incubated on the mucosal side. Endotoxin was added to the submucosal side at concentrations of 1 and 10 EU/ml, respectively. Under gassing with carbogene at 37 degreesC, the potential difference across the mucosa was measured continuously. Samples of the mucosal and submucosal solutions were removed at 60, 120, and 180 min and plated out on McConkey ampicillin-agar. After 180 min, the mucosal specimens were retrieved and examined by light and scanning electron microscopy. No significant change in potential difference was observed in control or endotoxin-incubated mucosa within the observation period. Neither light nor scanning electron microscopy showed a significant change in the structure of the epithelium, mucosa, or submucosa. No significant translocation of the E. coli across the mucosa was seen. We concluded that endotoxin alone does not induce immediate structural and functional damage to rat cecal mucosa in vitro. Therefore, it seems unlikely that a short endotoxemia alone directly triggers bacterial translocation by disrupting intestinal mucosa, but rather, entotoxin induces a local and systemic inflammatory reaction that leads to mucosal disruption.