Endothelium mediated aortic relaxation and blood pressure lowering effect of a procyanidin rich fraction of the stembark extracts of Erythrophleum suaveolens

A procyanidin-rich fraction of the stembark extracts of Erythrophleum suaveolens induced significant dose-dependent (0.1-100 μg/ml) relaxation of the guinea pig and rat aortic ring segments precontracted with noradrenaline (10μM) and potassium chloride (KCl, 30mM). However, the extract produced more significant relaxation in aortic rings with endothelium intact (+E) than in those without endothelium (-E). The plant extract produced a relaxation effect of 54.35 ± 3.53% in rat aortic rings in the presence of endothelium. The relaxation was 10.18 ± 1.64% in the rat endothelium-denudated aortic rings. The procyanidin fraction (30μg/ml) also prevented NA-induced contraction of aortic rings while 10 mg/kg provoked a fall in blood pressure of over 30 mm Hg a few seconds after extract administration with gradual return to the initial level. A 0.33mg/ml procyanidin fraction also produced over 86.6% inhibitory effect on angiotensin converting enzyme (ACE) activity, indicating a possible blood pressure lowering effect through vasodilation. These results indicate vasodilating properties on aortic rings which are endothelium mediated due to the liberation of nitric oxide leading to the lowering of blood pressure.