Endothelin-1 Increases Vascular Superoxide via Endothelin A –NADPH Oxidase Pathway in Low-Renin Hypertension

Abstract

Background— Angiotensin II–induced hypertension is associated with NAD(P)H oxidase–dependent superoxide production in the vessel wall. Vascular superoxide level is also increased in deoxycorticosterone acetate (DOCA)–salt hypertension, which is associated with a markedly depressed plasma renin activity because of sodium retention. However, the mechanisms underlying superoxide production in low-renin hypertension are undefined. Methods and Results— This study investigated (1) whether and how endothelin-1 (ET-1), which is increased in DOCA-salt hypertensive rats, contributes to arterial superoxide generation and (2) the effect of gene transfer of manganese superoxide dismutase and endothelial nitric oxide synthase. Both superoxide and ET-1 levels were significantly elevated in carotid arteries of DOCA-salt rats compared with that of the sham-operated controls. ET-1 concentration-dependently stimulated superoxide production in vitro in carotid arteries of normotensive rats. The increase in arterial superoxide in both ET-1–treated normotensive and DOCA-salt rats was reversed by a selective ET_A receptor antagonist, ABT-627, the flavoprotein inhibitor diphenyleneiodonium, and the NADPH oxidase inhibitor apocynin but not by the nitric oxide synthase inhibitor N^ω-l-arginine methyl ester or the xanthine oxidase inhibitor allopurinol. Furthermore, in vivo blockade of ET_A receptors significantly reduced arterial superoxide levels, with a concomitant decrease of systolic blood pressure in DOCA-salt rats. Ex vivo gene transfer of manganese superoxide dismutase or endothelial nitric oxide synthase also suppressed superoxide levels in carotid arteries of DOCA-salt rats. Conclusions— These findings suggest that ET-1 augments vascular superoxide production at least in part via an ET_A/NADPH oxidase pathway in low-renin mineralocorticoid hypertension.