NADPH oxidase-derived superoxide augments endothelin-1-induced venoconstriction in mineralocorticoid hypertension

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 ETA receptors, resulting in enhanced venoconstriction in DOCA-salt hypertensive rats. Treatment with ET-1 (0.01 to 1 nmol/L), but not the selective ETB receptor agonist sarafotoxin s6c, of vena cavas of normal rats concentration-dependently increased superoxide levels, an effect that was abolished by the selective ETA 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(-9) 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 ETA 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.