Objective: To study the effects of Changkang formula (CF) on plasma P substance (SP) and colon vasoactive intestinal peptide (VIP) in rats with diarrhea-predominant irritable bowel syndrome (D-IBS)

and to explore its possible mechanism on D-IBS. Method: Sixty Sprague-Dawley rats were randomly divided into 6 groups: the normal control group (normal saline)

model group (normal saline)

the maleate trimebutine group (15 mg·kg-1)

the low-

middle and high-dose CF groups (1.1

2.2

4.4 g·kg-1). The D-IBS model was induced in rats by senna-free drinking and stress-restrainting for 4 weeks. The corresponding medicines were intragastrically administered to rats once daily for 3 weeks. The abdominal withdrawal reflex (AWR) was scored. The levels of SP in serum and VIP in tissue were detected by using the ELISA assay. Result: Compared with the normal group

AWR score and plasma SP level increased

colon VIP level decreased in the model group (P<0.05

P<0.01). Compared with the model group

AWR score and plasma SP level decreased

colon VIP level increased in the low-

middle and high-dose CF groups (P<0.05

P<0.01). Conclusion: CF had a therapeutic effect on D-IBS by improving visceral hypersensitivity

reducing the level of plasma SP

and elevating the level of colon VIP in rats.