Objective: To investigate the action mechanism of Dihuang Yinzi on hypertension progress of spontaneously hypertensive rats (SHR)

and understand the role of endothelial function recovery by Dihuang Yinzi. Method: Fifty- four male SHR were divided into three groups: the control; Dihuang Yinzi treatment; and captoril treatment. Dihuang Yinzi (crude drug 15.9 g ·kg-1 ·d-1) and captoril (3.375 g ·kg-1 ·d-1) were treated from wk 7 to wk 24 (wk=week) through gavage. The drug effect was observed at wk 18 and wk 24 during the treatments and 8 wk (wk32) after treatment. Experiments including the blood pressure by arterial carotis cannula; the concentration of NO-2by Griess; the Ach-dependent relaxation of mesenteric rings by isometric tension change; and the mRNA expressions of IL-1

IL-6

TNF-α and iNOS of aorta tissue by real time PCR. Result: Dihuang Yinzi significantly reduced blood pressure at wk18

and increased Ach-dependent relaxation of mesenteric rings and the NO-2 concentration in serum at wk18 and wk24. The mRNA expression of IL-1

IL-6

TNF-α and iNOS was markedly inhibited by the herb formula. Although captopril showed stronger anti-hypertensive effect

which could not extended after drug withdraw. In addition

the beta blocker did not enhance Ach-dependent vasodilation. NO-2levels in serum and IL-1

IL-6 expression of aorta tissue were increased by captopril

while iNOS and TNF-α were inhibited at wk 24. Conclusion: Dihuang Yinzi showed anti-hypertensive effect with enhanced endothelium-dependent vasodilation in mesenteric artery and increased NO-2concentration in serum. Furthermore

the herb formula also exerted anti-inflammatory effect by decreasing IL-1

IL-6

TNF-α and iNOS expression.