Angiotensin II Infusion Alters Vascular Function in Mouse Resistance Vessels: Roles of O ^–·2 and Endothelium

Abstract

We hypothesized that prolonged angiotensin II (AngII) infusion would alter vascular reactivity by enhancing superoxide anion (O^–·2) generation. Male C57BL/6 mice were infused with AngII at 400 ng/kg/min (n = 16, AngII mice) or vehicle (n = 16, sham mice) for 2 weeks via subcutaneous osmotic minipumps. Contraction and relaxation of mesenteric resistance vessels (MRVs) were assessed using a Mulvany-Halpern myograph. AngII infusion increased systolic blood pressure, MRV NADPH oxidase activity and expression of p22^phox mRNA. Contraction to norepinephrine was unchanged, but AngII infusion increased contractile responses to AngII (41 ± 5 vs. 10 ± 4%, p < 0.001) and endothelin-1 (ET-1; 95 ± 10 vs. 70 ± 9%, p < 0.05), which was normalized by tempol (10^–4 M, a stable membrane-permeable superoxide dismutase mimetic) and ebselen [10^–5 M, a peroxynitrite (ONOO^–) scavenger]. Endothelium removal enhanced MRV contraction to AngII and ET-1 in sham mice but blunted these contractile responses in AngII mice. Relaxation to ACh was impaired in AngII mice (60.1 ± 8.8 vs. 83.2 ± 3.5%, p < 0.01), which normalized by tempol, whereas relaxation to sodium nitroprusside was similar in both groups. N-nitro- L-arginine (NNLA, a nitric oxide synthase inhibitor), partially inhibited acetylcholine relaxation of vessels from sham mice but not from AngII mice. The residual endothelium-dependent hyperpolarizing-factor-like relaxation was not different between groups. In conclusion,the AngII slow pressor response in mouse MRVs consisted of specific contractile hyperresponsiveness and impairment in the NO-mediated component of endothelium-dependent relaxation, which was mediated by O^–·2 and ONOO^– in the vascular smooth muscle cell.