Objective To investigate the expression of 5-hydroxytryptamine (5-HT) and its receptor (5-HT1AR) in severe acute pancreatitis (SAP) rats with intestinal motility disorder.Methods A total of 48 adult SD rats were evenly divided into sham operation group (SO group) and SAP group.There were 24 rats in each group.The SAP model was induced by retrograde injection of 3.5％ sodium taurocholate (1 mL/kg) into biliopancreatic duct.After modeling,at one,three,six and 12 hour time point six rats of each group were sacrificed and the venous blood was extracted.The levels of amylase and lipase were detected by automatic biochemical analyzer.The content of 5-HT and interleukin-6 (IL-6) were measured by enzyme-linked immunosorbent assay(ELISA).The tissues of 10 cm apart from trans-ligament jejunum,terminal ileum and sigmoid colon were collected and the expression of 5-HT1AR in the tissues at protein level was detected by Western blotting.At one,three,six and 12 hour after modeling,the expression of 5-HT1A R positive cells in the mucosa tissues of jejunum,terminal ileum and sigmoid colon of the rats in the two groups was observed by immunohistochemical and the area was calculated.The data were analyzed by t test.Results The levels of serum amylase,lipase,5 HT and IL-6 of SAP group were all significantly higher than those of SO group at three,six,12 hour after modeling (serum amylase level:(12 708±321),(24 507± 532),(18 097±424) U/L; serum lipase level:(69±4),(357±99),(264±87) U/L; serum 5-HT level:(1145±74),(1577±79),(1216±86)ng/mL; serum IL-6 level:(67±7),(112±11),(83± 8) pg/mL) (t=89.51,108.46,98.68,10.39,7.82,6.24,12.30,23.05,12.55,10.94,15.70,13.76; all P＜0.01).Compared with SO group,the expressions of 5-HT1AR proteins at six hour after modeling and the area of 5-HT1AR positive cells in the jejunum ((1.58±0.35) × 104,(1.43±0.34) × 104 and (1.49±0.32) × 104 μm2),terminal ileum ((1.49 ± 0.31) × 104,(1.36 ± 0.35) × 104 and (1.33±0.27) × 104 μm2) and sigmoid colon ((1.53±0.29)× 104,(1.43±0.33) × 104 and (1.56± 0.37) × 104 μm2) at three,six,12 hour after modeling of SAP group significantly decreased,the differences were statistically significant (t=10.72,9.92,10.83,10.07,11.09,11.39,10.67,12.22,9.34; all P＜0.01).Conclusions In SAP rats with intestinal motility disorder,the secretion of 5-HT significantly increased,however the expression of 5-HT1AR decreased.The ineffective combination of the two parts may be one of the important reasons for SAP with intestinal motility disorder.