Species-specific Spasmolytic Effect of Aspalathus linearis Aqueous Crude Extract

Objectives: Aspalathus linearis (Burm. f.) R. Dahlgren, or rooibos as it is commonly known, is a local plant of South Africa. The plant is used tradi tionally in gastrointestinal (GI) conditions like diarrhoea, colic, and cramps. It is also used to help in respiratory disorders like asthma. This endeavour aimed to provide scientific justification for the traditional uses of this herb. Methods: An aqueous extract (Al.Cr) of the fermented variety of rooibos tea (dried leaves and stems) was prepared. This extract was tested for pharmacological activity on guinea-pig ileum and rabbit trachea tissue preparations. Results: Rooibos tea extract, in previous studies conducted in isolated rabbit jejunum tissues, had shown a GI relaxant effect predomi nantly mediated via a K+ channel opening (KCO) mechanism. When Al.Cr extract was administered on K+ 80 mM and 25 mM sustained contractions in guinea-pig ileum, it was unable to exhibit a blocking activity up to 10 mg/ml. This indicated that the extract does not possess any Ca2+ channel blocking (CCB) or K+ channel opening (KCO) activity. The extract, from 1-5 mg/ml, was able to displace and suppress acetylcholine (ACh) concentration- response curves (CRC) in the ileal tissues. ACh mediated the GI stimulant effect from 0.01-3 μM. When investigated for a potential bronchodilator activity in rabbit trachea, Al.Cr, from 1-10 mg/ml, completely suppressed the carbachol (1 μM)-induced spasmogenicity. Conclusion: Findings from this study demonstrate a GI antispasmodic effect of Al.Cr in ileal tissues that came about through a non-CCB and non-KCO mechanism. Al.Cr also showed a bronchodilator effect in isolated rabbit trachea tissue preparations.  These results point to the value of this herb in GI and respiratory disorders.