Oxidative stress accompanies angiotensin (ANG) II infusion, but the role of ANG type 1 vs. type 2 receptors (AT 1-R and AT2-R, respectively) is unknown. We infused ANG II subcutaneously in rats for 1 wk. Excretion of 8-isoprostaglandin F 2␣ (8-Iso) and malonyldialdehyde (MDA) were related to renal cortical mRNA abundance for subunits of NADPH oxidase and superoxide dismutases (SODs) using real-time PCR. Subsets of ANG II-infused rats were given the AT 1-R antagonist candesartan cilexetil (Cand) or the AT 2-R antagonist PD-123,319 (PD). Compared to vehicle (Veh), ANG II increased 8-Iso excretion by 41% (Veh, 5.4 Ϯ 0.8 vs. ANG II, 7.6 Ϯ 0.5 pg/24 h; P Ͻ 0.05). This was prevented by Cand (5.6 Ϯ 0.5 pg/24 h; P Ͻ 0.05) and increased by PD (15.8 Ϯ 2.0 pg/24 h; P Ͻ 0.005). There were similar changes in MDA excretion. Compared to Veh, ANG II significantly (P Ͻ 0.005) increased the renal cortical mRNA expression of p22 phox (twofold), Nox-1 (2.6-fold), and Mn-SOD (1.5-fold) and decreased expression of Nox-4 (2.1-fold) and extracellular (EC)-SOD (2.1-fold). Cand prevented all of these changes except for the increase in Mn-SOD. PD accentuated changes in p22 phox and Nox-1 and increased p67 phox . We conclude that ANG II infusion stimulates oxidative stress via AT 1-R, which increases the renal cortical mRNA expression of p22 phox and Nox-1 and reduces abundance of Nox-4 and EC-SOD. This is offset by strong protective effects of AT 2-R, which are accompanied by decreased expression of p22 phox , Nox-1, and p67 phox . O 2 Ϫ ⅐ interacts with esterified or free arachidonate to yield a family of isoprostanes that includes 8-isoprostane prostaglandin F 2␣ (8-Iso). The steady-state excretion of 8-Iso reflects oxidative stress (38). There is evidence of enhanced oxidative stress during prolonged infusion of ANG II (36) and in models of ANG IIdependent hypertension (2,8,22,24,48). However, the roles of AT 1 -R vs. AT 2 -R in the generation of oxidative stress and the expression of NADPH oxidase and SOD in kidneys has not been established.The first aim of this study was to determine the effects of AT 1 -and AT 2 -R blockade on the excretion of 8-Iso during a "slow-pressor" dose of ANG II. Because isoprostanes also can be generated by metabolism of arachidonate via cyclooxygenase (19,33), additional studies assessed the excretion of an arachidonate-independent marker of lipid peroxidation, malonyldialdehyde (MDA). The second aim was to investigate the effects of these perturbations on the renal expression of the mRNAs for the components of NADPH oxidase and SOD isoforms.

Abstract. The hypothesis that a high salt (HS) intake increases oxidative stress was investigated and was related to renal cortical expression of NAD(P)H oxidase and superoxide dismutase (SOD). 8-Isoprostane PGF 2␣ and malonyldialdehyde were measured in groups (n ϭ 6 to 8) of conscious rats during low-salt, normal-salt, or HS diets. NADPH-and NADH-stimulated superoxide anion (O 2 ·Ϫ ) generation was assessed by chemiluminescence, and expression of NAD(P)H oxidase and SOD were assessed with real-time PCR. Excretion of 8-isoprostane and malonyldialdehyde increased incrementally twoto threefold with salt intake (P Ͻ 0.001), whereas prostaglandin E 2 was unchanged. Renal cortical NADH-and NADPHstimulable O 2 ·Ϫ generation increased (P Ͻ 0.05) 30 to 40% with salt intake. Compared with low-salt diet, HS significantly (P Ͻ 0.005) increased renal cortical mRNA expression of gp91 phox and p47 phox and decreased expression of intracellular CuZn (IC)-SOD and mitochondrial (Mn)-SOD. Despite suppression of the renin-angiotensin system, salt loading enhances oxidative stress. This is accompanied by increased renal cortical NADH and NADPH oxidase activity and increased expression of gp91 phox and p47 phox and decreased IC-and Mn-SOD. Thus, salt intake enhances generation of O 2 ·Ϫ accompanied by enhanced renal expression and activity of NAD(P)H oxidase with diminished renal expression of IC-and Mn-SOD.

We tested the hypothesis that superoxide anion (O(2)(-).) generated in the kidney by prolonged angiotensin II (ANG II) reduces renal cortical Po(2) and the use of O(2) for tubular sodium transport (T(Na):Q(O(2))). Groups (n = 8-11) of rats received angiotensin II (ANG II, 200 ng.kg(-1).min(-1) sc) or vehicle for 2 wk with concurrent infusions of a permeant nitroxide SOD mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol, 200 nmol.kg(-1).min(-1)) or vehicle. Rats were studied under anesthesia with measurements of renal oxygen usage and Po(2) in the cortex and tubules with a glass electrode. Compared with vehicle, ANG II increased mean arterial pressure (107 +/- 4 vs. 146 +/- 6 mmHg; P < 0.001), renal vascular resistance (42 +/- 3 vs. 65 +/- 7 mmHg.ml(-1).min(-1).100 g(-1); P < 0.001), renal cortical NADPH oxidase activity (2.3 +/- 0.2 vs. 3.6 +/- 0.4 nmol O(2)(-)..min(-1).mg(-1) protein; P < 0.05), mRNA and protein expression for p22(phox) (2.1- and 1.8-fold respectively; P < 0.05) and reduced the mRNA for extracellular (EC)-SOD (-1.8 fold; P < 0.05). ANG II reduced the Po(2) in the proximal tubule (39 +/- 1 vs. 34 +/- 2 mmHg; P < 0.05) and throughout the cortex and reduced the T(Na):Q(O(2)) (17 +/- 1 vs. 9 +/- 2 mumol/mumol; P < 0.001). Tempol blunted or prevented all these effects of ANG II. The effects of prolonged ANG II to cause hypertension, renal vasoconstriction, renal cortical hypoxia, and reduced efficiency of O(2) usage for Na(+) transport, activation of NADPH oxidase, increased expression of p22(phox), and reduced expression of EC-SOD can be ascribed to O(2)(-). generation because they are prevented by an SOD mimetic.

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Tempol corrects hypertension without a compensatory sympathoadrenal activation or salt retention. The response is independent of nitric oxide, endothelin, or catecholamines and occurs despite increased PRA. It is accompanied by a reduction in oxidative stress and is maintained during increased salt intake.