Role of Oxidative Stress in Endothelial Dysfunction and Enhanced Responses to Angiotensin II of Afferent Arterioles from Rabbits Infused with Angiotensin II

Abstract

ABSTRACT. The hypothesis that O2·− enhances angiotensin II (AngII)-induced vasoconstriction and impairs acetylcholine-induced vasodilation of afferent arterioles (Aff) in AngII–induced hypertension was investigated. Rabbits (n = 6 per group) received 12 to 14 d of 0.154 M NaCl (Sham), subpressor AngII (60 ng/kg per min; AngII 60) or slow pressor AngII (200 ng/kg per min; AngII 200). Individual Aff were perfused in vitro at 60 mmHg. AngII 200 increased mean arterial pressure (mean ± SD; 103 ± 9 versus 73 ± 6 mmHg; P < 0.01), plasma lipid peroxides (2.6 ± 0.3 versus 2.0 ± 0.3 nM; P < 0.05), renal cortical NADPH- and NADH-dependent O2·− generation, and Aff mRNA for p22phox 5-fold (P < 0.001) but decreased that for AT1-receptor 2.4-fold (P < 0.01). AngII 60 increased only NADH-dependent O2·− generation by renal cortex. Aff from AngII 200 rabbits had diminished acetylcholine relaxations (+50 ± 4 versus +85 ± 6%; P < 0.001), but these became similar in the presence of nitro-l-arginine (10−4 M). Aff from AngII 60 and AngII 200 rabbits had unchanged norepinephrine contractions (10−7 M) but significantly (P < 0.05) enhanced AngII contractions (10−8 M: Sham −52 ± 5 versus AngII 60 to 77 ± 5 versus AngII 200 to 110 ± 10%). The superoxide dismutase mimetic tempol (10−4 M) moderated the AngII responses of Aff from AngII 200 rabbits to levels of AngII 60 rabbits (−64 ± 7%). The AngII slow pressor response enhances renal cortical O2·− and p22phox expression. Increased O2·− generation in Aff mediates an impaired nitric oxide synthase–dependent endothelium-derived relaxing factor response and paradoxically enhances contractions to AngII despite downregulation of the mRNA for AT1 receptors. A subpressor dose of AngII enhances Aff responses to AngII independent of O2·−. E-mail: wilcoxch@georgetown.edu