Objective To investigate the potential protective effects of valproic acid (VPA) on gut barrier function after major burn injury in rats and its mechanism.Methods Forty male Sprague-Dawley (SD) rats were divided into sham + normal saline (NS),sham + VPA,scald + NS,and scald + VPA groups,with 10 rats in each group.Rat with 55％ total body surface area (TBSA) third-degree severe-bums model was reproduced by immersing into 80 ℃ water,and the rats in sham groups were given sham-bums by immersing into 37 ℃ water.The rats after severebums were immediately treated with 0.25 mL of 300 mg/kg VPA or NS by subcutaneous injection.Rats were sacrificed at 2 hours and 6 hours after injury,and abdominal aortic blood and ileal tissue were harvested.The levels of vascular endothelial growth factor (VEGF) were determined by enzyme-linked immunosorbent assay (ELISA).The intestinal permeability was evaluated by fluorescein isothiocyanate-dextran (FITC-dextran) determination.The histomorphological changes in gut barrier were evaluated by Chiu grading system.Levels of acetylated lysine at the ninth position of histone 3 protein (Ac-H3K9),hypoxia-inducible factor 1α (HIF-1α),zona occludens 1 (ZO-1) and myosin light chain kinase (MLCK) were determined by immunofluorescence staining and Western Blot.Results Compared with sham + NS group,rats in scald + NS group showed intestinal mucosal damage 2 hours after bum injury,as well as increased mucosal permeability,protein expression levels of HIF-1 α,VEGF,MLCK,and lowered levels of AC-H3K9 and ZO-1.These changes were much more prominent at 6 hours after injury.VPA treatment significantly attenuated the bum-induced intestinal damage.Compared with scald + NS group,the protective effects in scald + VPA group was not evident at 2 hours after injury;however,intestinal damage was much less severe at 6 hours after injury (Chiu score:2.03 ± 0.27 vs.3.12 ± 0.15),intestinal permeability was significantly decreased [FITC-dextran (μg/L):709 ± 76 vs.1138 ± 75],histone acetylation was enhanced [Ac-H3K9 (gray value):1.55 ± 0.12 vs.0.48±0.12],ZO-1 degradation was significantly inhibited (gray value:0.69 ± 0.12 vs.0.43 ± 0.16),the protein expression levels of VEGF and MLCK were significantly down-regulated [VEGF (ng/mg):51.7±3.7 vs.71.2±4.3,MLCK (gray value):1.98±0.20 vs.2.80±0.24],while the HIF-1 α protein expression levels were significantly reduced at both 2 hours and 6 hours after injury (gray value:2.50±0.39 vs.3.88±0.42 at 2 hours,1.83±0.42 vs.4.42±0.41 at 6 hours,all P ＜ 0.05).Conclusions Severe bum injury can induce histone deacetylation,ZO-1 degradation and intestinal barrier dysfunction.VPA can improve the levels of histone acetylation and ZO-1,and protect intestinal epithelial barrier function.These may probably be mediated through inhibiting HIF-1α and its downstream gene VEGF and MLCK.