Abstract：OBJECTIVE: Severe infection is a common cause of gastrointestinal dysfunction in children, the mechanism of which is closely related to endotoxemia and impairment of gut mucosal barrier function. The study was undertaken to investigate intestinal epithelial apoptosis and its possible signal-conducting pathway in rats with endotoxemia. METHODS: The model of endotoxemia was established by intraperitoneal injection of endotoxin (4 mg/kg of Escherichia coli O_ 55∶B_5 lipopolysaccharide) in 40 18-day-old rats (Endotoxin group). Another 40 rats, served as controls and received normal saline (1 mL/kg). Both groups of rats were sacrificed at 2, 4, 6, 24 and 72 hrs after injection. A segment, 4-cm-long, of lower ileum was then removed. The pathologic changes of small intestine villus were observed under an optical microscope (hematoxylin-eosin staining). Apoptosis was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Caspase-3 expression was measured by immunohistochemistry staining. RESULTS: The structure of small intestinal villi of the Control group remained normal at various time points, while inflammation cells infiltration was observed in the Endotoxin group 4-72 hrs after injection. The apoptotic cells significantly increased 2 hrs after endotoxin injection, and peaked at 24 hrs. The apoptotic index of the Endotoxin group at each time point was significantly higher than that of the Control group (P<0.001). Similarly, the Caspase-3 expression in the Endotoxin group at each time point was significantly higher than that of the Control group. The Caspase-3 expression increased 2 hrs after endotoxin injection and reached a peak at 6 hrs. CONCLUSIONS: Intestinal epithelial apoptosis increases in rats with endotoxemia. Caspase-3 expression is one of its signal-conducting pathways. Cellular apoptosis might be the underlying mechanism of gut mucosal barrier impairment during severe infection.
