Objective To investigate the potential mechanism of abdominal paracentesis drainage(APD)on severe acute pancreatitis(SAP)through regulating Toll-like receptor 4(TLR4)expression in rat intestine.Methods Male SD rats were randomized into the Sham group,SAP group,and APD group,with 15 rats in each group.Rats were treated with a retrograde injection of 5%sodium taurocholate into the pancreatic bile duct to induce SAP,followed by ADP treatment through placing a drainage tube in the right lower abdomen of rats.Rats without ADP treatment were used as controls:SAP group included rats without ADP surgical procedure;while Sham group included rats with ADP surgical procedure but without placing a drainage tube.About 24 hours after ADP treatment,pathological changes of small intestine and pancreas were observed by HE staining;serum amylase and lipase activities were detected by the automatic biochemical analyzer;serum endotoxin levels were detected by limulus amebocyte lysate method;serum DAO activity was detected by ultraviolet colorimetry;TNF-α,IL-6 and D-lactic acid levels were detected by ELISA;apoptosis of intestinal mucosal epithelial cells was detected by TUNEL assay;mRNA expression of TLR4 was detected by real-time PCR;the expression of TLR4 signaling pathway and apoptosis-related proteins were detected by immunohistochemistry and Western blotting.Results Compared with SAP rats,the pathological damage of small intestine and pancreas of APD rats was significantly reduced;the pathological score was decreased(P<0.05);serum amylase,lipase and DAO activity,serum TNF-α,IL-6,D-lactic acid and endotoxin levels were also declined(P<0.05).The expression of TLR4,MyD88,NF-κB p65,TNF-α and IL-6 in the small intestine was significantly lower in the APD group than those in the SAP group(P<0.05).In addition,compared with the SAP group,apoptotic index,cleaved caspase-3,and Bax expression were significantly decreased in the APD group,while Bcl-2 expression was increased(P<0.05).Conclusion Early implementation of APD can significantly reduce the expression of intestinal TLR4 in SAP rats,reduce the activation of a downstream inflammatory signaling pathway,and thus decrease the occurrence of intestinal mucosal epithelial cell apoptosis that contributes to intestinal protection.