The efficacy of STW 5 in irritable bowel syndrome partly involves serotonin as a mediator in the brain-gut axis

Introduction To study the involvement of serotonin in the action of an herbal medicine, STW 5, an experimental model of irritable bowel syndrome (IBS) was used.

Method IBS was induced experimentally in male Wistar rats by exposing them to restraint stress (RS) for 1 hour/day for a week. Two groups of animals were given STW 5 orally in doses of 1 and 2.5 ml/kg of the commercial preparation during that period, while another group was given Itopride (as a reference standard drug) in a dose of 20 mg/kg. STW 5 is a herbal preparation (Iberogast^®​, Bayer Consumer Health, Darmstadt, Germany) consisting of a hydroalcoholic extract of nine herbs, with proven clinical efficacy in functional dyspepsia and IBS.

Results One day after the 2-week experimental period, the animal body weight was assessed as well as the fecal transit time, before sacrificing the animals and excising the colon, hippocampus and cerebral cortex. Colon homogenates were used to estimate reduced glutathione (GSH), malondialdehyde (MDA) and nitric oxide (NO) contents. Serotonin was also measured in the colon as well as in the brain tissues. RS tended to decrease the body weight and to delay fecal transit time. The serotonin content in the colon was reduced, while that in the hippocampus and cortex was elevated. GSH in colonic tissues was reduced while MDA was elevated. Nitric oxide levels were raised in the brain tissues but decreased in the colon. All changes induced by RS tended to be prevented by treatment with both Itopride and STW 5 at both dose levels. The results confirm the elevation of oxidative stress parameters in colonic tissue following RS as well as a reduction of the excitatory transmitter, serotonin, thereby reducing fecal output in affected rats. In the brain, chronic exposure to stress tends to enhance the activity of enzymes involved in serotonin and noradrenaline synthesis, explaining the present findings.

Conclusion The results lends further support to the involvement of the brain gut axis in the beneficial use of STW 5 in IBS, albeit at least partly through regulating the role of serotonin.

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Artikel online veröffentlicht:
13. Juni 2022