Vasoconstrictor and Inotropic Effects Induced by the Root Bark Extracts of Anthocleista schweinfurthii

Abstract

The present study was undertaken to investigate the cardiovascular effect of three extracts from the root bark of Anthocleista schweinfurthii Gilg.: an aqueous extract (A_E), a dichloromethane extract (DCMR) and a fraction enriched in cardiac glycoside type compounds (CARDAN). In isolated perfused frog heart, bolus injection of the extracts produced a positive inotropic effect. The responses to A_E and DCMR, but not to CARDAN, were depressed by propranolol. In isolated rat aorta, DCMR produced a transient increase in contractile tension while A_E and CARDAN induced a sustained constriction. A_E vasoconstrictor effect was abolished by phentolamine, while contraction evoked by CARDAN was antagonized by verapamil. In aortic rings contracted in low K⁺ media, the addition of K⁺ evoked a relaxation, which was abolished by ouabain, depressed by DCMR but not affected by either A_E or CARDAN. These observations indicate that Anthocleista schweinfurthii contains substances that promote vasoconstriction and increase cardiac contraction. The effect of DCMR was only partially mediated by inhibition of the Na⁺ pump while the mechanism of action of A_E and CARDAN was distinct from the inhibition of the Na⁺,K⁺-ATPase pump, but could involve adrenergic receptors, or either direct or indirect activation of L-type calcium channels.