Developmental changes in distribution of the mucous gel layer and intestinal permeability in rat small intestine.

Abstract

From the developmental aspects, the distribution of fluorescein isothiocyanate dextran 70,000 (FTTC-dextran) and mucous gel across the lumen of small intestine was observed as an investigation into the role of mucous gel on intestinal permeability. Furthermore, the effect of N-acetyl cysteine (NAC), a mucolytic agent, on intestinal permeability was examined. In suckling and weaned rats, FTTC-dextran (750 mg/kg body wt) was gavage-fed. After 3 hours, blood samples were taken by cardiac puncture to analyze plasma FTTC-dextran by fluorescence spectrometry. Samples of small intestine with luminal contents were frozen and sectioned in a cryostat for fluorescence microscopy; the same sections were placed in a 0.2% celloidin solution to preserve mucous gel and were stained by periodic acid-Schiff reaction for light microscopy. In weaned rats, intestinal permeability was examined with different concentrations of intraluminally instilled NAC. The plasma level of FTTC-dextran showed a significant increase (p < .01) in suckling rats compared with the weaned rats. Morphologic findings were similar in both the jejunum and ileum: The spaces between villi were not entirely filled with mucus but filled with FTTC-dextran in suckling rats, whereas the spaces were filled with mucus and not filled with FTTC-dextran in weaned rats. Intestinal permeability in groups with NAC were significantly higher (p < .01) than that in group without NAC. These results suggest that an increase in the mucous gel layer that coats the epithelial lining according to the maturation of the gastrointestinal tract is one of the most important factors for a restriction in intestinal permeability.