Tongbian formula alleviates slow transit constipation by increasing intestinal butyric acid to activate the 5-HT signaling.

Slow transit constipation (STC) is a long-lasting and prevalent intestinal condition, marked by hard, dry feces. The primary cause of STC may be attributed to an imbalance in the gut's microbial community and alterations in its metabolic byproducts. Tongbian formula (TB), a traditional Chinese medicinal formula, has been used to treat STC and shows a great effect on relieving constipation. The role of TB in regulating intestinal microbiota has not been fully elucidated. Herein, we investigated the potential effect of TB on gut microbiota and further explored the potential mechanism behind its effects. Our study demonstrated that TB significantly increased fecal water content and intestinal ink propulsion rate in loperamide (Lope)-induced STC rats. 5-HT signaling was suppressed in STC colon tissue, and the abundance of butyric acid (BA) in colonic contents was significantly down-regulated after Lope treatment. Notably, TB administration led to the restoration of microbial dysbiosis and the up-regulation of BA content, subsequently activating 5-HT signaling pathways. When BA was combined with a tryptophan hydroxylase-1 (TPH1) inhibitor, which is crucial for 5-HT synthesis, its therapeutic efficacy for treating STC was compromised. TB alleviates STC by reversing the intestinal microbiota imbalance and activating the 5-HT signaling in the colon through increasing BA levels. These findings suggest that TB is an ideal candidate for STC treatment.