Coleonema album: studies of the pharmacological action on smooth muscle in vitro and antimicrobial action of its essential oil.

The mode of action of the essential oil of Coleonema album, a South African species from the Cape region, was studied on smooth muscle in vitro using field-stimulated guinea-pig ileum. The oil produced an initial spasmogenic activity followed by spasmolysis, both actions being dose-dependent. The spasmolytic action was post-synaptic and not atropine-like and was unaffected by the adrenoceptor blockers phentolamine and propranolol. There was no evidence for the involvement of either cyclic guanosine monophosphate or cyclic adenosine monophosphate in the spasmolytic activity. The oil had some calcium channel blocking activity but this is not the primary explanation for its spasmolytic response. Antimicrobial activity against Pseudomonas aeruginosa, Escherichia coli, Staphyloccocus aureus and Saccharomyces cerevisiae was very low and totally absent against Enterococcus hirae, suggesting that the oil has no worthwhile potential in this area. However, as the oil has a very disagreeable odour in its undiluted form, it could be a powerful insect repellent, as its local usage suggests, and this remains to be investigated.