Endothelium-dependent and independent vasorelaxant effect of Terminalia superba (Combretaceae) on rat aorta

Abstract

Terminalia superba (Combretaceae) is a plant which is used in Cameroon for the treatment of many diseases including arterial hypertension. The vasorelaxant effect of the aqueous stem bark extract of T. superba was evaluated on the isolated aorta rings of the rat constricted with KCl (60 mM) or norepinephrine (10-5 M). Cumulative concentrations (20-100 µg/mL) of T. superba provoked a dose-dependent relaxation of the thoracic aorta precontracted by norepinephrine or KCl. The maximum vasorelaxant activity of T. superba was 107.24 ± 7.01% on the intact aorta and 102.48 ± 19.09% on the denuded aorta contracted by norepinephrine. The evaluation of the effects of the aqueous extract of T. superba on the intact aorta precontracted by KCl showed a maximum relaxation of 68.43 ± 2.51% at a final concentration of 100µg/mL. The vasorelaxation induced by T. superba (100 µg/mL) on the intact aorta precontracted by norepinephrine was significantly reduced in the presence of Nw-nitro-L-arginine methyl ester (54.98 ± 6.0%, p<0.01), tetraethylammonium (58.93 ± 5.30%, p<0.05) or propranolol (69.39 ± 4.03%, p<0.05). Indometacin (10-4 M), or glibenclamide (5 µM), did not modify significantly the vasorelaxant effect of the plant extract. These results suggest that the vasorelaxation elicited by T. superba was not mediated via endothelium-derived prostacyclin or ATP-sensitive K+ channels. The direct effects of T. superba seem to be mediated by beta-adrenergic receptors and potassium channels other than potassium ATP-dependent channels. The results of this study could explain, at least partly, the use of this plant in empirical treatment of arterial hypertension.