Vasorelaxant and hypotensive effects of Sclerocarya birrea (A Rich) Hochst (Anacardiaceae) stem bark aqueous extract in rats.

The vasorelaxant and hypotensive effects of Sclerocarya birrea stem bark aqueous extract have been examined in rat experimental paradigms. Cumulative additions of S birrea stem bark aqueous extract (SBE 12.5-200 mg/ml) to the bath fluid induced concentration-dependent relaxations of endothelium- containing normotensive Wistar rat isolated aortic rings pre-contracted with noradrenaline (NA). The vasorelaxant effect of SBE on endothelium-containing isolated aortic rings was annulled by removal of the functional endothelium (in endothelium-denuded normotensive Wistar rat isolated aortic rings), or by pretreatment of the endothelium-containing isolated aortic rings with NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS). Bolus intravenous administrations of the plant extract (SBE 25-400 mg/kg iv) caused transient, dose-dependent and significant (p < 0.05-0.001) reductions in systemic arterial blood pressure and heart rates of anaesthetised normotensive and hypertensive Dahl salt-sensitive rats. The findings of this experimental animal study suggest that S birrea stem bark aqueous extract relaxes normotensive Wistar rat aortic vascular smooth muscle via endothelium-dependent nitric oxide (NO); and that the hypotensive effect of the plant extract is likely to be mediated, at least in part, through nitric oxide synthase activation and subsequent nitric oxide release.