NADPH Oxidase–Derived Superoxide Augments Endothelin-1–Induced Venoconstriction in Mineralocorticoid Hypertension

Abstract

Abstract-Deoxycorticosterone acetate (DOCA)-salt hypertension is characterized by low renin/angiotensin but increased arterial superoxide levels. We have recently reported that the arterial endothelin-1 (ET-1) level is increased, resulting in NADPH oxidase activation and superoxide generation. However, the effect of ET-1 on venous superoxide production and its relation to venoconstriction are unknown. The present study tested the hypotheses that ET-1 stimulates venous NADPH oxidase and superoxide via its ET A receptors, resulting in enhanced venoconstriction in DOCA-salt hypertensive rats. Treatment with ET-1 (0.01 to 1 nmol/L), but not the selective ET B receptor agonist sarafotoxin s6c, of vena cavas of normal rats concentration-dependently increased superoxide levels, an effect that was abolished by the selective ET A receptor antagonist ABT-627. Although the ET-1 level was not increased in the vena cava and plasma, both venous NADPH oxidase activity and superoxide levels were significantly higher in DOCA-salt compared with sham rats. Moreover, ET-1 treatment (10 Ϫ9 mol/L, 10 minutes) of isolated vena cavas further elevated superoxide levels in DOCA-salt rats only but not sham rats, an effect that was abrogated by the superoxide scavenger tempol. Similarly, ET-1-induced contractions of isolated vena cavas of DOCA-salt but not sham rats were significantly inhibited by tempol. The NADPH oxidase inhibitor apocynin significantly reduced superoxide levels in vena cavas of DOCA-salt rats and in ET-1-treated vena cavas of normal rats. Finally, in vivo ET A receptor blockade by ABT-627 significantly lowered venous superoxide levels and blood pressure in DOCA-salt but not sham rats. These results suggest that superoxide contributes to ET-1-induced venoconstriction through an elevated venous NADPH oxidase activity in mineralocorticoid hypertension. Ϫ ) contributes to hypertension development in both animals and humans by inactivating nitric oxide (NO) and impairing arterial endothelium-dependent relaxation. 1-3 An increase in venous O 2 Ϫ might also inactivate NO and alter venous functions (eg, impaired relaxation or augmented constriction). However, the role of venous O 2 Ϫ production in hypertension and its effect on venoconstriction are unknown. Because hypertension involves multifactorial hemodynamic alterations, venoconstriction augmented by O 2 Ϫ might contribute to increased blood pressure by enhancing cardiac output and shifting blood from the veins to arteries. 4 -6 Consistent with this notion, endothelin-1 (ET-1) stimulates venous constriction, resulting in significant changes in blood volume distribution, cardiac output, and blood pressure. 5,6 The factors controlling venoconstriction are complex and include both neural and humoral mechanisms. The increased sympathetic nerve activity results in augmented venoconstriction, which predominates in the development of spontaneous hypertension. 4 Various humoral factors, such as angiotensin II (Ang II) and ET-1, also induce venoconstriction. 7 Ang II causes impair...

Characteristics and actions of NAD(P)H oxidase on the sarcoplasmic reticulum of coronary artery smooth muscle

“…It has been demonstrated that, in addition to the interactions of O 2 Ϫ ⅐ and NO in endothelium-dependent vasodilation, the redox signaling mechanism is involved in the constrictor response of arterial smooth muscle to a variety of agonists such as angiotensin II (12,15,17), arginine vasopressin (25), norepinephrine (44), thromboxane A 2 (46,58), and endothelin (6,25). Moreover, endogenous O 2 Ϫ ⅐ has been reported to participate in the vascular myogenic response and the vascular reaction to electrical stimulation (14,19,36,41).…”

Endothelin, Angiotensin, and Oxidative Stress in Hypertension

“…51 Similarly, chronic ET-1 infusion is associated with Despite mixed results using the antioxidant tempol, there is clear evidence that ET stimulates superoxide production through an NADPH oxidase-dependent manner in DOCA-salt hypertensive rats. 55,56 Because ET A receptor blockade and superoxide scavenging can attenuate the hypertension associated with DOCA-salt treatment, it is reasonable to hypothesize that ETdependent hypertension could be inhibited by disruption of NADPH oxidase subunit assembly with the inhibitor, apocynin. Elmarakby et al have recently demonstrated that apocynin inhibits the increase in oxidative stress associated with chronic ET-1 infusion, yet the resulting hypertension was unaffected.…”

“…55,56 Because ET A receptor blockade and superoxide scavenging can attenuate the hypertension associated with DOCA-salt treatment, it is reasonable to hypothesize that ETdependent hypertension could be inhibited by disruption of NADPH oxidase subunit assembly with the inhibitor, apocynin. Elmarakby et al have recently demonstrated that apocynin inhibits the increase in oxidative stress associated with chronic ET-1 infusion, yet the resulting hypertension was unaffected.…”

Endothelin-1, superoxide and adeninediphosphate ribose cyclase in shark vascular smooth muscle

“…) and reactive oxygen species (ROS) in VSM (Sedeek et al, 2003;Touyz et al, 2004;Li et al, 2003;Galle et al, 2000;Wedgwood et al, 2001). In cultured rat aortic VSM cells, ET-1 dose dependently (10 -8 to 10 -6 mol·l -1 ) increased the formation of O 2 .- (Sedeek et al, 2003) and, in human gluteal VSM cells, similar results were noted (Touyz et al, 2004).…”