To detect the expression of 5-HT in the colon of rats with constipation by establishing the model of slow transit constipation (STC), and to explore the correlation between 5-HT and STC.

Forty-eight SD rats were randomly divided into 4 groups: blank group, model group, mosapride group, maren pill group. The rats of blank group were given normal saline by gastric irrigation, while the rats of model group and treatment groups were given diphenoxylate by intragastric administration before treated. When established the model of STC, the rats of treatment groups were respectively given mosapride, maren pills, and the stool grain and stool wet weight were observed. The proximal colons were collected . Expression of 5-HT in the proximal colon by immunohistochemistry were detected. The staining results were analyzed semi-quantitively by computerized color image analyzer as the following parameter: mean density. Data were analyzed by ANOVA.

The density means (MD) of 5-HT in the colon of model group (0.453±0.028) was greater than the control group (0.148±0.011) (t=34.209, P<0.001), mosapride group (0.316±0.012) (t=15.307, P<0.001), maren pill group (0.291±0.010) (t=18.296, P<0.001), and the difference was statistically significant; The density means (MD) of mosapride group (0.316±0.012) (t=35.983, P<0.001) and maren pill group (0.291±0.010) (t=31.919, P<0.001) were higher than control group, which the difference was statistically significant.

The increased expression of 5-HT in the colon of rats with constipation may affect on the intestinal nerve conduction function, which led to the incidence of constipation.