The herbal preparation STW 5 affects serotonergic pathways in the brain and colon as well as stress parameters in experimental irritable bowel syndrome.

Background: Exposure to stress has been related to disturbance in 5‐hydroxytryptamine (5‐HT) signaling in the brain‐gut axis and is considered as a major predisposing factor for the development of irritable bowel syndrome (IBS). The present study aimed to investigate the possible involvement of 5‐HT and some other stress‐related parameters in the effectiveness of STW 5 against stress‐induced IBS. Methods: Rats were subjected to restraint stress (RS) for 1 h/day for 14 consecutive days to induce IBS‐like symptoms and were given STW 5 orally at the same time. At the end of the experiment, blood samples were withdrawn, then animals were euthanized and the brain hippocampi, cerebral cortices, as well as colons were isolated for biochemical and histopathological assessments. Results: RS increased the plasma corticotrophin releasing factor (CRF) with concomitant increase in hippocampal and cortical 5‐HT levels, as well as mast cell inflammatory mediators, oxidative stress biomarkers, and histopathological inflammatory changes observed in rat colon. It also decreased the colonic content of 5‐HT with consequent decrease in fecal pellet output (FPO). Treatment with STW 5 protected against these changes. Conclusion: The protective effect of STW 5 against RS‐induced IBS is related to its ability to normalize the induced changes in 5‐HT in the brain‐gut axis and counteract the stress‐induced oxidative stress and inflammation. [ABSTRACT FROM AUTHOR]