Tong-Xie-Yao-Fang decoction has proven to be effective for irritable bowel syndrome (IBS) , a common intestinal disease. However, there are few studies on the main active ingredients in the decoction.

To examine the effects of Tong-Xie-Yao-Fang disassembled recipes on the expression levels of brain-derived neurotrophic factor (BDNF) and substance P (SP) in colon and hippocampus in a rat model of diarrhea-predominant irritable bowel syndrome (IBS-D) .

On July 2020, a total of 32 6-week-old SPF male Wistar rats were selected and randomized into blank group, model group, baishao-fangfeng group (B-F group) and chenpi-baizhu group (C-B group) , with 8 rats in each. Except for the blank group, the other three groups were used to establish visceral sensitive IBS-D rat model by use of colorectal dilatation + chronic restraint stress. At the end of successful model creation, the B-F group received the solution extracted from both baishao and fangfeng using gavage administration (4 ml/kg) , C-B group received the solution extracted from both chenpi and baizhu using gavage administration (4 ml/kg) , and the other two groups received gavage administration of distilled water. This treatment period was 14 days for all groups. The weight and growth status of weight, stool classification according to the Bristol Stool Scale (BSS) , abdominal withdrawal reflex (AWR) under different pressure gradients, BDNF and SP expression levels in colon and hippocampus were compared between the four groups at the end of modeling and subsequent treatment.

All rats survived when the IBS-D model was successfully created. Blank group had bigger average growth of weight after modeling period than both B-F and C-B groups (P<0.05) . B-F and C-B groups had bigger average growth of weight after the treatment than model group (P<0.05) . Compared with model group, blank group had lower average score of BSS after treatment, and so did both B-F and C-B groups (P<0.05) . After the treatment, the AWR score under 60 mm Hg of cuff pressure in the model group was higher than that in the blank group (P<0.05) , and under both 60 mm Hg or 80 mm Hg of cuff pressure, the AWR score in the B-F group was lower than that in model group or C-B group (P<0.05) . Model group had higher average post-treatment expression levels of BDNF and SP in colon tissue than both blank group and B-F group, and so did C-B group (P<0.05) . Model group had lower average post-treatment expression level of BDNF in hippocampus than blank group (P<0.05) . B-F group had higher average post-treatment expression level of BDNF in hippocampus than both model group (P<0.05) . Model group had higher average post-treatment expression level of SP in hippocampus than both blank group and B-F group (P<0.05) . C-B group had higher expression level of SP in hippocampus than blank group (P<0.05) .

Both Tong-Xie-Yao-Fang disassembled recipes could significantly improve weight and diarrhea in rat model of IBS-D. Compared with chenpi and baizhu, baishao and fangfeng could better alleviate intestinal hypersensitivity, and down-regulate SP expression level in colon and hippocampus, and BDNF expression level in colon, up-regulate the BDNF expression level in colon, and regulate the balance of related brain-gut peptides.