Adaptive cytoprotection in the small intestine: role of mucus

Gastric mucosal injury induced by strong irritants can be dramatically reduced by pretreating the mucosa with mild forms of the same irritant. This phenomenon has been termed "adaptive cytoprotection." The aim of the present study was to use in vivo and in vitro approaches to study adaptive cytoprotection in the small intestine using physiologically relevant concentrations of oleic acid. Anesthetized rats were instrumented for perfusion of the proximal jejunum with 10 or 40 mM oleic acid (in 20 mM sodium taurocholate). Mucosal epithelial integrity was continuously monitored by measuring the blood-to-lumen clearance of 51Cr-labeled EDTA. Perfusion of the lumen with 40 mM oleic acid produced a 10-fold increase in 51Cr-EDTA clearance, which was not affected by a previous perfusion with 10 mM oleic acid, i.e., no adaptive cytoprotection. In another series of experiments, oleic acid was placed in the lumen rather than perfused, and mucosal epithelial integrity was assessed histologically. Intraluminal placement of 10 mM oleic acid resulted in the generation of a mucus layer over the epithelium. Subsequent placement of 40 mM oleic acid did not produce significant epithelial cell injury, i.e., adaptive cytoprotection. In in vitro studies, mucin (1, 5, and 10 mg/ml) was layered over confluent monolayers of Caco-2 cells prior to addition of 2 mM oleic acid in 4 mM sodium taurocholate. The epithelial cell injury induced by oleic acid was inhibited by mucin in a dose-dependent manner. Further studies indicate that mucin does not prevent, but simply delays, the onset of cell injury.(ABSTRACT TRUNCATED AT 250 WORDS)