Objective: To study the mechanism of Tongxie Yaofang (TXYF) in rat model of diarrhea-predominant irritable bowel syndrome (D-IBS). Method: Forty male Wistar rats were divided randomly into normal group

model group

TXYF group

antagonism group. The rat D-IBS model was established by binding stress for 18 d

after D-IBS model was established suceesful

TXYF group and TXYF+antagonism group were orally given TXYF at a dose of 23.6 g·kg-1

once a day for 7 d

meanwhile antagonism group was iv given vasoactine intrestinal peptide(VIP) antagonist at a dose of 35 μg·kg-1 for once a day 4 d after 4 d of being given TXYF. The water content in rat feces was determined. The method of reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry was used to determine the expression of aquaporin-8(AQP8) in colon tissue. Result: ① The water content in rat feces

compared with normal group

in TXYF group was higer(P<0.01)

and compared with model group

in TXYF group the water content was significantly reduced (P<0.01)

but in antagonism group no change was found. ②The colon expression level of AQP8

compared with model group

the expression of AQP8 in TXYF group was significantly increased (P<0.01)

but in antagonism group no change was observed. Conclusion: The mechanism of TXYF in treatment of D-IBS may be related to regulating the secretion of VIP and up-regulating the AQP8 expression in colon tissue.