Abstract:
The leaf of nelumbo nucifera Gertn. (N. nucifera), an oriental herbal medicine, has been shown to improve health well-being and posses antihypertensive effects. Its vascular effect has not yet been studied. The purpose of this study is to investigate the potential vasorelaxant activity and mechanisms of leaf extract of N. nucifera (NN) in isolated aortic rings from normotensive and hypertensive rats induced by constriction of left renal artery. Thoracic aortic rings isolated from both groups of rats were placed in organ baths and constricted with a sub-maximal dose of phenylephrine (α1 adrenergic receptor agonist). Then, the relaxant responses to cumulative concentration of NN (10-100 up/ml) were examined. NN-induced concentration-dependent relaxation was observed in aortic rings of normotensive and hypertensive rats in a similar degree (85.39 ± 4.5% and 83.8 ± 5.8% respectively). In the presence of L-NAME (nitric oxide synthase inhibitor, 100 uM), the vasorelaxant effects of NN in normotensive and hypertensive aorta were significantly attenuated to 28.46 ± 7.25% and to 51.52 ± 23.29% respectively, suggesting that the relaxation is partially mediated via nitric oxide (NO). The inhibition effect of L-NAME was significantly greater in normotensive rings than in hypertensive ones (p < 0.05), thereby indicating an endothelium impairment in hypertensive state. Both propranolol (β-adrenergic receptor antagonist, 50 uM), and atropine (muscarinic receptor antagonist, 1 uM) showed no significant effect on NN-induced relaxation in both groups. In comparison to the intact endothelium ones. The denuded endothelium rings from normotensive rats showed significantly smaller vasorelaxant responses to NN (16.45 ± 3.24% vs 45.33 ± 11.53%, P< 0.05). In conclusion, these results show that NN can produce vasorelaxation, which may account for its antihypertensive action. The effects of NN are both endothelium-dependent and endothelium-independent mechanisms, and the former may be mediated through NO.