Antispasmodic effects of Rooibos tea (Aspalathus linearis) is mediated predominantly through K+ -channel activation.
Basic Clin Pharmacol Toxicol. 2006 Nov;99(5):365-73. PMID: 17076689
Rooibos tea has been widely used for abdominal spasm and diarrhoea. The aim of the present study was to explore the possible mechanism for its use in such ailments. Its aqueous extract (RT) at 0.3-10 mg/ml produced relaxation of spontaneous and low K(+) (25 mM)-induced contractions of rabbit jejunum, with weak effect on high K(+) (80 mM)-induced contractions. In the presence of glibenclamide, relaxation of low K(+)-induced contractions was prevented. Cromakalim inhibited contractions induced by low K(+), but not high K(+), while verapamil did not differentiate in its inhibitory effect on contractions produced by the two concentrations of K(+). RT also exhibited antidiarrhoeal and antisecretory activities in mice. The spasmolytic effect was concentrated in organic fractions. Its constituents, chrysoeriol, orientin and vitexin showed a similar pattern of spasmolytic effects to the extract, while rutin was more like verapamil. So Rooibos tea possesses a combination of dominant K(ATP) channel activation and weak Ca(++) antagonist mechanisms and hence justifies its use in hyperactive gastrointestinal disorders.