The herbal combination STW 5 (Iberogast®) has shown to be effective against functional gastrointestinal diseases in several randomised controlled double blind studies. It is widely used in therapy for more than four decades, having a very favourable safety profile [1]. Recent experiments showed that STW 5 was able to decrease 5-HT mediated sensory nerve stimulation in the GIT [2] and that it has binding affinities to 5-HT4 and to a lesser extent to 5-HT3 receptors [3]. Our present study aimed to investigate the possible effects of STW 5 on 5-HT3 receptors of the guinea pig ileum in order to further elucidate of its mechanisms of action.
The response of the isolated guinea pig ileum to the specific 5-HT3 agonist, SR 52772 (3–100µM) was tested in vitro by measuring the contractions evoked by increasing doses of the agonist. The measurement of dose response relationship was repeated in the presence of different concentrations of STW 5, applied as an ethanol free lyophilisate, in the bath.
At a bath concentration of 1 and 3µg/ml, STW 5 induced a parallel shift of the dose response curve of SR 52772 to the right. The contraction induced by SR57227 (100µM) was decreased by STW 5 to 77% (1µg/ml) and to 51% (3µg/ml), respectively. Effects were statistically significant and indicate an antagonistic effect of STW 5 on 5-HT3 receptors.
The results indicate a possible involvement of 5-HT3 receptor antagonism in the gastrointestinal effects of STW 5 (Iberogast®).
References: [1] Rösch, W., et al. (2006) Phytomedicine 113 S V 114–121. [2] Liu, C. et al. (2004) Neurogastroenterol.Motil. 16: 759–764. [3] Simmen, U. et al. (2006) Phytomedicine 13 S V:51–55
