Fluorescein isothiocyanate (FITC)-dextran permeability assay.

Intestinal epithelial barrier function was measured in vivo, using a 4-kDa fluorescein isothiocyanate (FITC)-dextran probe (Sigma-Aldrich) in serum. Rats were fasted overnight, followed by orogastric gavage of FITC-dextran (100 μl; 88 mg/ml in sterile PBS). After 4 h, rats were briefly exposed to gaseous carbon dioxide and euthanized by cervical dislocation. Blood samples were obtained via cardiac puncture and placed on ice until use. Blood samples were centrifuged at 5,000 rpm (4°C; 20 min), and then sera were collected. The FITC-dextran concentrations in the sera were determined by fluorometry (34).