Spasmolytic effect of aqueous extract of Tagetes erecta L. flowers is mediated through calcium channel blockade on the guinea-pig ileum

This study provides pharmacological evidence on the spasmolytic activity of Tagetes erecta L. (marigold or cempasúchil) on the guinea-pig ileum and presents data on its mechanism of action. The relaxant effect on KCl contractions was more marked with aqueous (AqEx) than with ethanol extracts (EtEx) of T. erecta flowers (55.6 ± 11.0 vs 21.1 ± 4.4%, respectively). In addition, the aqueous extract antagonized contractions elicited by EFS, but not by acetylcholine (73.5 ± 1.9 vs 14.5 ± 5.3%, respectively). These effects were not diminished by hexamethonium or L-NAME, but this extract caused a rightward shift in the Ca²⁺ concentration-response curves like that of verapamil. Quercetin and rutin, two flavonoids present in this plant, also showed spasmolytic effects (95.7 ± 2.8 and 27.9 ± 7.1%, respectively). Interestingly, in tissues without spasmogens, the extract induced contractions superimposed on their spontaneous activity. These results support the traditional use of T. erecta as a spasmolytic in folk medicine and suggest mainly that quercetin could be partly responsible for this effect. The spasmolytic effect appears to involve voltage-gated calcium channels, but not the nitric oxide pathway or the release of neurotransmitters from enteric neurons. Nevertheless, this plant could produce colic or stomachache as adverse effects in clinical situations in which these symptoms are not originally present.