| Objective:A stable rat model of heat exposure was established to investigate whether PARP-1 inhibitor(pj34) might affect the intestinal epithelial TJ barrier permeability,and to investigate the mechanism by observe the changes of TJ protein(occludin) expression.Methods:Anesthetized rats were exposed to 42℃in a ventilated chamber to establish a stable model of heat exposure.The rectal temperature was measured by a thermometer every 10 min.The heat exposure extent was controlled which produced about 10-20%mortality(24h) In preliminary experiment,changes of intestinal epithelial barrier permeability and TJ protein occludin expression were investigated on 0h,2h,6h,8h,12h,24h after heat exposure.2h after heat exposure had the most significant changes and was selected as the best intervention effect observing time point.In intervention experiment,SD rats were randomly divided into three groups(n≥6):Intervention group(I) which was given pj34 lh before heat exposure;Vehicle control group(V) which was given normal saline;and Normal control group(N).The three groups were given heat exposure.At 2h after heat exposure,the effect of pj34 on intestinal epithelial barrier permeability was observed through changes of plasma FD4,endotoxin and cytokines concentration.The general and micro pathology were observed by light microscope(hematoxylin and eosin-staining,HE staining) and transmission electron microscope(TEM).Occludin expression were investigated by western blot,immunofluorescent and immunochemistry.Results: In preliminary experiment,the anesthetic rats exposed to 42℃,the rectal temperature upgrade velocity was 0.5℃/5min.The rectal temperature reached about 42℃at 50min,the 24h mortality was 16%.In six observing time points, plasma endotoxin concentration was highest and occludin expression was lowest at 2h after heat exposure.So at 2h after heat exposure,the damage of heat exposure was strongest,and it's the best intervention effect observing time point. In intervention experiment,at 2h after heat exposure,intestinal epithelial barrier permeability(FD4,endotoxin and cytokines concentration) of vehicle control group was significantly higher than normal control group(p＜0.05),but plasma FD4 concentration of pj34 intervention group was significantly decreased than V group(P＜0.05),the plasma endotoxin and cytokines concentration between these two groups also had significant deviation(P＜0.05)o In morphology, observing the ight micrographs of HE jejunal tissue,the sloughing of epithelium off the basement membrane at the villus tips of the heat exposure groups tissue(I, V groups) compared with the normal control tissue.In many visual field(VF) (＞6VF / slice),this phenomenon was not universal.But the extent of epithelium sloughing in I group was obviously relieved.Under TEM,TJ of normal enterocytes was integrated with the compact zonal structure.At 2h after heat exposure,TJ of V group was break with widen intercellular space,and the density of TJ was decreased.In enterocytes of I group,structure of TJ was integrated with higher density than V group.In normal small intestinal tissue,the fluorescence signal distribute along the cell membrane.The fluorescence intensity of I group was similar to N group,while the signal was obviously decreased in V group.The results of immunochemistry and western blot were coordinate with it (P＜0.05).Conclusion:PARP-1 inhibitor,pj34,increased occludin expression, strengthen the intestinal epithelial TJ,which is the prevention target of pj34 to intestinal epithelial tight junction barrier heat damage,so pj34 decreased the heat exposure induced high intestinal epithelial barrier permeability,produced a marked protective effect.
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