Effect of heat stroke on small intestinal epithelial tight junction protein occludin in rats

Abstract

Objective A stable rat model of heat stroke was established to investigate heat stroke-induced changes of the intestinal epithelial tight junction (TJ) barrier permeability, and to investigate the mechanism by observing the changes of TJ protein (occludin) expression and TJ morphology. Methods SD rats were randomly divided into two groups(n = 10): heat stroke group and normal control group. Stable model of heat stroke was established. Anesthetized rats were exposed to 42 ℃ in a ventilated chamber for 50min, after heat exposure, the rats were placed in room temperature(26 ℃ ) for 2 h. Then the rats were sacrificed and samples were taken. The effect of heat stroke on intestinal epithelial barrier permeability was observed through changes of plasma FD4 and endotoxin concentration, cytokines concentration was detected as inflammatory indicators. The general and micro pathology was observed by light microscope (hematoxylin and eosin-staining, HE staining) and transmission electron microscope (TEM). Occludin expression was investigated by Western bloting and immunochemistry. Results At 2 h after heat exposure, intestinal epithelial barrier permeability( FD4 and endotoxin concentration), and cytokines levels of heat stroke group were significantly higher than normal control group(P ＜ 0. 05 ). In morphology, by observing the light micrographs of HE jejunal tissue, the sloughing of epithelium off the basement membrane at the villus tips of the heat stroke group compared with the normal controlgroup. In many visual fields (VF)( ≥6VF/slice), this phenomenon was not universal. Under TEM, TJ of normal enterocytes was integrated with the compact zonal structure. At 2 h after heat exposure, TJ of heat stroke group was broken with widen intercellular space, and the density of TJ was decreased. In immunochemistry assay, the positive signal was distributed along the cell membrane in normal small intestinal tissue, while the signal was obviously decreased in heat stroke group.The results of Western bloting showed that occludin expresion of heat stroke group was significantly lower than normal control group(P ＜0.05). Conclusion Heat stroke decreased occludin expression, opened the intestinal epithelial TJ, which destroyed intestinal epithelial tight junction barrier, induced high intestinal epithelial barrier permeability, produced endotoxemia and systemic inflammatory response syndrome (SIRS). Key words: Heat stroke; Intestinal epithelial barrier; Tight junction; Occludin