Aim of the study: The stem bark of Terminalia superba (Combretaceae) (TS) is used in traditional Cameroonian medicine as antihypertensive remedy. In the present study, we investigated the vasorelaxant properties of different extracts of TS and their underlying mechanisms.
Materials and methods: Activities of aqueous (AQU), methanolic (MET), methylene chloride (MC), and methylene chloride-methanol (MCM) extracts of TS were evaluated on isolated rat aortic rings precontracted with phenylephrine (PE) or high KCl.
Results: All extracts induced a vasodilating effect both on KCl- and PE-induced contractions. The effects of MC and MCM extracts were greater than those of AQU or MET extracts (P<0.05). MC had an endothelium-independent effect and reduced Ca(++)-induced contraction following PE or KCl challenge (P<0.05). After incubation with verapamil, MC induced a relaxation in rings precontracted by PE (P<0.001). By contrast, the effect of MCM was endothelium-dependent and decreased by the nitric oxide synthase inhibitor N(W)-nitro-L-arginine methyl ester (P<0.05).
Conclusions: These data demonstrate that the MC extract exhibits vasorelaxant effects that are partly due to inhibition of extracellular Ca(++) influx and/or inhibition of intracellular Ca(++) release in vascular smooth muscle cells. By contrast, the effect of the MCM extract was found to be endothelium- and nitric oxide dependent.
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