We have used peptide-directed antibodies to each major renal Na transporter and channel proteins to screen renal homogenates for changes in Na transporter protein expression after initiation of dietary NaCl restriction. After equilibration on a NaCl-replete diet (2.0 meq · 200 g body wt−1 · day−1), rats were switched to a NaCl-deficient diet (0.02 meq · 200 g body wt−1 · day−1). Na excretion fell to 25% of baseline levels on day 1, followed by a further decrease <4% of baseline levels on day 3, of NaCl restriction. The decreased Na excretion at day 1 occurred despite the absence of a significant increase in plasma aldosterone level or in the abundance of any of the major renal Na transporters. However, after a 1-day lag, plasma aldosterone levels increased in association with increases in abundances of three aldosterone-regulated Na transporter proteins: the thiazide-sensitive Na-Cl cotransporter (NCC), the α-subunit of the amiloride-sensitive epithelial Na channel (α-ENaC), and the 70-kDa form of γ-ENaC. RNase protection assays of transporter mRNA levels revealed an increase in renal α-ENaC mRNA coincident with the increase in α-ENaC protein abundance. However, there was no change in NCC mRNA abundance, suggesting that the increase in NCC protein in response to dietary NaCl restriction was not a result of altered gene transcription. These results point to early regulatory processes that decrease renal Na excretion without an increase in the abundance of any Na transporter, followed by a late aldosterone-dependent response associated with upregulation of NCC and ENaC.

Dopamine is important in the pathogenesis of hypertension because of abnormalities in receptor-mediated regulation of renal sodium transport. Dopamine receptors are classified into D1-like (D1, D5) and D2-like (D2, D3, D4) subtypes, all of which are expressed in the kidney. Mice deficient in specific dopamine receptors have been generated to provide holistic assessment on the varying physiological roles of each receptor subtype. This review examines recent studies on these mutant mouse models and evaluates the impact of individual dopamine receptor subtypes on blood pressure regulation.

Abstract-Abnormalities in D 1 dopamine receptor function in the kidney are present in some types of human essential and rodent genetic hypertension. We hypothesize that increased activity of G protein-coupled receptor kinase type 4 (GRK4) causes the impaired renal D 1 receptor function in hypertension. We measured renal GRK4 and D 1 and serine-phosphorylated D 1 receptors and determined the effect of decreasing renal GRK4 protein by the chronic renal cortical interstitial infusion (4 weeks) of GRK4 antisense oligodeoxynucleotides (As-Odns) in conscious-uninephrectomized spontaneously hypertensive rats (SHRs) and their normotensive controls, Wistar-Kyoto (WKY) rats. Basal GRK4 expression and serine-phosphorylated D 1 receptors were Ϸ90% higher in SHRs than in WKY rats and were decreased to a greater extent in SHRs than in WKY rats with GRK4 As-Odns treatment. Basal renal D 1 receptor protein was similar in both rat strains. GRK4 As-Odns, but not scrambled oligodeoxynucleotides, increased sodium excretion and urine volume, attenuated the increase in arterial blood pressure with age, and decreased protein excretion in SHRs, effects that were not observed in WKY rats. These studies provide direct evidence of a crucial role of renal GRK4 in the D 1 receptor control of sodium excretion and blood pressure in genetic hypertension. The uncoupling of the D 1 -like receptor from its effector proteins in the kidney in hypertension is associated with increased phosphorylation of the D 1 receptor. 4,5 In human essential hypertension, single nucleotide polymorphisms of the G protein-coupled receptor (GPCR) kinase 4 (GRK4) are associated with constitutive phosphorylation and desensitization of the D 1 receptor in renal proximal tubules. 4 -6 These lead to sodium retention and hypertension. Indeed, transgenic mice expressing the GRK4 variant, GRK4␥A142V, develop hypertension that is associated with an impaired D 1 receptormediated natriuresis. 5 To determine whether aberrant GRK4 function contributes to the impaired renal D 1 receptor function in SHRs, we studied the renal expression of GRK4 and the effects of decreasing its expression in the kidney by a chronic renal cortical interstitial infusion of GRK4 antisense (As) oligodeoxynucleotides (Odns) in conscious SHRs and their normotensive controls, Wistar-Kyoto (WKY) rats. If an increased GRK4 activity in the kidney is responsible for the increased blood pressure in SHRs, this maneuver should improve D 1 receptor-mediated renal tubular handling of sodium and ameliorate the high blood pressure in SHRs without affecting these variables in WKY rats.

Abstract-Low rates of angiotensin II (Ang II) infusion raise blood pressure, renal vascular resistance (RVR), NADPH oxidase activity, and superoxide. We tested the hypothesis that these effects are ameliorated by extracellular superoxide dismutase (EC-SOD). EC-SOD knockout (Ϫ/Ϫ) and wild type (ϩ/ϩ) mice were equipped with blood pressure telemeters and infused subcutaneously with Ang II (400 ng/kg per minute) or vehicle for 2 weeks. During vehicle infusion, EC-SOD Ϫ/Ϫ mice had significantly (PϽ0.05) higher MAP (ϩ/ϩ: 107Ϯ3 mm Hg versus Ϫ/Ϫ: 114Ϯ2 mm Hg; nϭ11 to 14), RVR, lipid peroxidation, renal cortical p22 phox expression, and NADPH oxidase activity. Ang II infusion in EC-SOD ϩ/ϩ mice significantly (PϽ0.05) increased MAP, RVR, p22 phox , NADPH oxidase activity, and lipid peroxidation. Ang II reduced SOD activity in plasma, aorta, and kidney accompanied by reduced renal EC-SOD expression. During Ang II infusion, both groups had similar values for MAP (ϩ/ϩ Ang II: 125Ϯ3 versus Ϫ/Ϫ Ang II: 124Ϯ3 mmHg; P value not significant), RVR, NADPH oxidase activity, and lipid peroxidation. SOD activity in the kidneys of Ang II-infused mice was paradoxically higher in EC-SOD Ϫ/Ϫ mice (ϩ/ϩ: 8.8Ϯ1.2 U/mg protein Ϫ1 versus Ϫ/Ϫ: 13.7Ϯ1.6 U/mg protein Ϫ1 ; PϽ0.05) accompanied by a significant upregulation of mRNA and protein for Cu/Zn-SOD. In conclusion, EC-SOD protects normal mice against oxidative stress by attenuating renal p22 phox expression, NADPH oxidase activation, and the accompanying renal vasoconstriction and hypertension. However, during an Ang II slow pressor response, renal EC-SOD expression is reduced and, in its absence, renal Cu/Zn-SOD is upregulated and may prevent excessive Ang II-induced renal oxidative stress, renal vasoconstriction, and hypertension. Key Words: oxidative stress Ⅲ hypertension Ⅲ renal Ⅲ kidney Ⅲ renal circulation Ⅲ nitric oxide Ⅲ endothelium A n increase in reactive oxygen species (ROS) in the blood vessels and kidneys is reported in several experimental animal models of hypertension and in human essential and renovascular hypertension. 1 Infusions of angiotensin II (Ang II) increase blood pressure (BP), markers of oxidative stress, and renal expression of the p22 phox and Nox-1 components of renal NADPH oxidase. 2 These effects seem specific for Ang II, because similar pressor infusions of norepinephrine into rats do not induce oxidative stress in blood vessels. 3 An increased production of superoxide (O 2 ⅐Ϫ ) reduces bioactive NO 4 and contributes to vascular and renal injury in chronic hypertension. 5,6 O 2 ⅐Ϫ dismutase (SOD) metabolizes O 2 ⅐Ϫ to H 2 O 2 , which is further metabolized to inactive products by peroxidases. Hypertension can be moderated or prevented by gene transfer of extracellular (EC)-SOD 7 or by administration of tempol, 8 which is a nitroxide SOD mimetic.The 3 isoforms of SOD are localized to the kidney. 9 EC-SOD is located on cell membranes of endothelial cells and vascular smooth muscle cells. 10 EC-SOD Ϫ/Ϫ mice have endothelial dysfunction in conduit blood vessels th...

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Key Words: dopamine Ⅲ receptors, angiotensin II Ⅲ mice Ⅲ hypertension Ⅲ angiotensin II Ⅲ endothelin Ⅲ vasopressins E ssential hypertension is a major risk factor for the development of cardiovascular disease. 1 It is a heterogeneous disease in which both genetics and environment influence blood pressure. 2 Dopamine affects cardiovascular regulatory mechanisms by its actions on renal hemodynamics and ion and water transport and by its regulation of hormones and humoral agents, such as aldosterone, catecholamines, endothelin, prolactin, proopiomelanocortin, renin, and vasopressin. In addition, dopamine can control blood pressure by acting on neuronal cardiovascular centers, heart, and arterial and venous vessels. Methods Generation of D 4 Dopamine-Receptor Mutant MiceThe original F 2 hybrid strain (129/SvϫC57BL/6) carrying a mutant form of the D 4 dopamine receptor was initially generated and backcrossed to C57BL/6 mice. Heterozygous (D 4 ϩ/Ϫ ) mice were mated to obtain D 4 Ϫ/Ϫ and D 4 ϩ/ϩ littermates, and the D 4 Ϫ/Ϫ mice were backcrossed with C57BL/6 mice to obtain sixth-and tenthgeneration mice in the Department of Physiology and Pharmacology, Oregon Health and Science University. 21 We used sixth-generation mice for acute studies and tenth-generation mice for chronic and immunoblotting studies. All of the animals were genotyped 21 and treated in accordance with National Institutes of Health guidelines for ethical treatment and handling of animals in research.

Abstract-Dysfunction of D 2 -like receptors has been reported in essential hypertension. Disruption of D 2 R in mice (D 2 Ϫ/Ϫ ) results in high blood pressure, and several D 2 R polymorphisms are associated with decreased D 2 R expression. Because D 2 R agonists have antioxidant activity, we hypothesized that increased blood pressure in D 2 Ϫ/Ϫ is related to increased oxidative stress. D 2 Ϫ/Ϫ mice had increased urinary excretion of 8-isoprostane, a parameter of oxidative stress; increased activity of reduced nicotinamide-adenine dinucleotide phosphate oxidase in renal cortex; increased expression of the reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits Nox1, Nox2, and Nox4; and decreased expression of the antioxidant enzyme heme-oxygenase-2 in the kidneys, suggesting that regulation of reactive oxygen species (ROS) production by D 2 R involves both pro-oxidant and antioxidant systems. Apocynin, a reduced nicotinamide-adenine dinucleotide phosphate oxidase inhibitor, or hemin, an inducer of heme oxigenase-1, normalized the blood pressure in D 2 Ϫ/Ϫ mice. Because D 2 Rs in the adrenal gland are implicated in aldosterone regulation, we evaluated whether alterations in aldosterone secretion contribute to ROS production in this model. Urinary aldosterone was increased in D 2 Ϫ/Ϫ mice and its response to a high-sodium diet was impaired. Spirolactone normalized the blood pressure in D 2 Ϫ/Ϫ mice and the renal expression of Nox1 and Nox4, indicating that the increased blood pressure and ROS production are, in part, mediated by impaired aldosterone regulation. However, spironolactone did not normalize the excretion of 8-isoprostane and had no effect on expression of Nox2 or heme-oxygenase-2. Our results show that the D 2 R is involved in the regulation of ROS production and that, by direct and indirect mechanisms, altered D 2 R function may result in ROS-dependent hypertension. [1][2][3] There is abundant evidence that an intact dopaminergic system is necessary to maintain normal blood pressure and that genetic hypertension is associated with alterations in dopamine production and receptor function. [1][2][3][4] In humans and rodents, some dopamine receptor genes and their regulators are in loci linked to hypertension. 3,5 The natriuretic effect of D 1 -like agonists is impaired in genetically hypertensive rats 3,4 and in human essential hypertension. 3,4 Alterations in D 2 -like receptor function have also been reported in hypertension. 1,2 Loci in chromosome 11, where the D 2 R gene is located, are linked to hypertension. 5,6 A polymorphism in exon 6 of the D 2 R gene is associated with elevated blood pressure, 7 and a TaqI polymorphism is associated with human essential hypertension. 8 Several D 2 R polymorphisms are associated with decreased D 2 R expression 9,10 and affect D 2 R mRNA stability and synthesis of the receptor. 11 The disruption of any of the dopamine receptor genes in mice produces dopamine receptor subtype-specific hypertension. 3,[12][13][14] Specifically, disruption of the D 2 R...

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