Description:
<jats:p> 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<jats:sub>E</jats:sub>), 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<jats:sub>E</jats:sub> and DCMR, but not to CARDAN, were depressed by propranolol. In isolated rat aorta, DCMR produced a transient increase in contractile tension while A<jats:sub>E</jats:sub> and CARDAN induced a sustained constriction. A<jats:sub>E</jats:sub> vasoconstrictor effect was abolished by phentolamine, while contraction evoked by CARDAN was antagonized by verapamil. In aortic rings contracted in low K<jats:sup>+</jats:sup> media, the addition of K<jats:sup>+</jats:sup> evoked a relaxation, which was abolished by ouabain, depressed by DCMR but not affected by either A<jats:sub>E</jats:sub> 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<jats:sup>+</jats:sup> pump while the mechanism of action of A<jats:sub>E</jats:sub> and CARDAN was distinct from the inhibition of the Na<jats:sup>+</jats:sup>,K<jats:sup>+</jats:sup>-ATPase pump, but could involve adrenergic receptors, or either direct or indirect activation of L-type calcium channels. </jats:p>