Preglomerular Arterioles Research Articles

Abstract P247: Elastin Insufficiency Impairs Renal Hemodynamics And Accelerates Aging-associated Structural And Functional Remodeling Of Preglomerular Arterioles

Elastin degradation and fragmentation are hallmarks of arterial stiffness and renal dysfunction associated with aging. However, it is unclear whether elastin insufficiency contributes to the changes in the structure and function of the resistance vasculature of the kidney during aging. Here we determined how increased vascular stiffness due to elastin insufficiency alters renal hemodynamics and mechanical properties of preglomerular arterioles. We assessed renal hemodynamics under anesthesia in 14-16-month-old female wild type (WT) and elastin heterozygous ( Eln +/- ) mice. Renal autoregulation was assessed by a stepwise increase in renal perfusion pressure (RPP) by simultaneously occluding the superior mesenteric and celiac arteries. Myogenic constriction and arterial stiffness were assessed by pressure myography of isolated renal interlobar arteries. Baseline renal vascular resistance (RVR) was elevated in Eln +/- mice (13.8 ± 2.9 vs 11.2 ± 1.4 mmHg/μL/min/g left kidney weight), while systolic blood pressure (SBP; 75.1 ± 7.4 vs 91 ± 4.2mmHg), renal blood flow (RBF; 6.3 ± 1.2 vs 7.4 ± 1.7 μL/min/g left kidney weight), renal plasma flow (RPF; 3.4 ± 0.8 vs 5 ± 1.2 mL/min/g/ left kidney weight) and urine flow rate, all trended lower in Eln +/- mice compared to WT mice. Glomerular filtration rate (GFR) and filtration fraction (FF) were similar between the two groups. A stepwise increase in RPP caused a slower decline and rise in RBF and RVR, respectively, in Eln +/- relative to WT mice. The maximal changes in RBF (5 ± 1.1 vs 4.7 ± 0.8 μL/min/g left kidney weight), RVR (17.6 ± 7.3 vs 22.5 ± 2.1 mmHg/μL/min/g left kidney weight), urine flow rate,GFR, and FF were less robust in Eln +/- mice. RPF decreased in WT mice in response to raising RPP, whereas it remained unchanged in Eln +/- mice. Myogenic response and increases in elastic modulus and wall tension following stepwise changes in intraluminal pressure were all augmented in interlobar arteries from Eln +/- relative to WT mice. However, there was no difference in kidney weight/tibia length ratio between the two genotypes. We conclude that elastin insufficiency impairs renal hemodynamics by exacerbating age associated increase in vascular stiffness.

Impaired renal hemodynamics and glomerular hyperfiltration contribute to hypertension-induced renal injury

Recently, we reported a mutation in γ-adducin (ADD3) was associated with an impaired myogenic response of the afferent arteriole and hypertension-induced chronic kidney disease (CKD) in fawn hooded hypertensive (FHH) rats. However, the mechanisms by which altered renal blood flow (RBF) autoregulation promotes hypertension-induced renal injury remain to be determined. The present study compared the time course of changes in renal hemodynamics and the progression of CKD during the development of DOCA-salt hypertension in FHH 1BN congenic rats [wild-type (WT)] with an intact myogenic response versus FHH 1BN Add3KO (Add3KO) rats, which have impaired myogenic response. RBF was well autoregulated in WT rats but not in Add3KO rats. Glomerular capillary pressure rose by 6 versus 14 mmHg in WT versus Add3KO rats when blood pressure increased from 100 to 150 mmHg. After 1 wk of hypertension, glomerular filtration rate increased by 38% and glomerular nephrin expression decreased by 20% in Add3KO rats. Neither were altered in WT rats. Proteinuria doubled in WT rats versus a sixfold increase in Add3KO rats. The degree of renal injury was greater in Add3KO than WT rats after 3 wk of hypertension. RBF, glomerular filtration rate, and glomerular capillary pressure were lower by 20%, 28%, and 19% in Add3KO rats than in WT rats, which was associated with glomerular matrix expansion and loss of capillary filtration area. The results indicated that impaired RBF autoregulation and eutrophic remodeling of preglomerular arterioles increase the transmission of pressure to glomeruli, which induces podocyte loss and accelerates the progression of CKD in hypertensive Add3KO rats.

Involvement of proinflammatory cytokines in angiotensin�II‑induced hypertension in rat

Rightfully considered as essential for hydro-electrolytic homeostasis, angiotensin II (Ang II) is the main product of the renin-angiotensin system (RAS). Ang II is one of the most important factors that contribute to the regulation of systemic arterial blood pressure (ABP). This major role is based on the effects exerted by RAS: Upon the kidney (RAS involvement in the control of salt and water excretion), upon the brain (RAS involvement in the control of water intake), and upon the sympathetic nervous system. It is currently known that there is a tight bidirectional link between high ABP and chronic kidney disease (CKD). Ang II causes vasoconstriction in the renal microvasculature, predominantly in the preglomerular arterioles. High ABP affects the target organs (eyes, brain, heart, kidneys) and it is known both as a cause and as an effect of CKD. Thus, there is a positive feedback mechanism that contributes even more to the increase in ABP and the progression of CKD. Along with its main hemodynamic effects, Ang II has direct proinflammatory actions, that also affect the structure and function of the kidney and heart. This study investigated the role of RAS and Ang II in the inflammation that accompanies the hypertension experimentally induced by Ang II in rats. Our data support the hypothesis that anti-inflammatory medication might alleviate the morphological and/or functional changes of the kidneys and heart that are related to Ang II-induced hypertension.

Glucagon-like peptide-1 receptors in the kidney: impact on renal autoregulation.

Glucagon-like peptide-1 (GLP-1) and strategies based on this blood sugar-reducing and appetite-suppressing hormone are used to treat obesity and type 2 diabetes. However, the GLP-1 receptor (GLP-1R) is also present in the kidney, where it influences renal function. The effect of GLP-1 on the kidney varies between humans and rodents. The effect of GLP-1 on kidney function also seems to vary depending on its concentration and the physiological or pathological state of the kidney. In studies with rodents or humans, acute infusion of pharmacological doses of GLP-1 stimulates natriuresis and diuresis. However, the effect on the renal vasculature is less clear. In rodents, GLP-1 infusion increases renal plasma flow and glomerular filtration rate, suggesting renal vasodilation. In humans, only a subset of the study participants exhibits increased renal plasma flow and glomerular filtration rate. Differential status of kidney function and changes in renal vascular resistance of the preglomerular arterioles may account for the different responses of the human study participants. Because renal function in patients with type 2 diabetes is already at risk or compromised, understanding the effects of GLP-1R activation on kidney function in these patients is particularly important. This review examines the distribution of GLP-1R in the kidney and the effects elicited by GLP-1 or GLP-1R agonists. By integrating results from acute and chronic studies in healthy individuals and patients with type 2 diabetes along with those from rodent studies, we provide insight into how GLP-1R activation affects renal function and autoregulation.

Deletion of the 20‐HETE receptor (GPR75) impairs myogenic tone of renal preglomerular arteries

20‐Hydroxyeicosatetraenoic acid (20‐HETE), one of the principal cytochrome P450 (CYP)‐derived eicosanoids, is a potent vasoactive lipid whose vascular effects include stimulation of smooth muscle contractility, migration and proliferation, as well as endothelial cell dysfunction and inflammation. Increased levels of 20‐HETE in experimental animals and in humans are associated with hypertension, stroke, myocardial infarction and vascular diseases. We recently identified GPR75, an orphan G‐protein (Gaq/11) coupled receptor (GPCR), as a specific cellular target to which 20‐HETE binds and through which it activates a signaling cascade that culminates in many of the functional outcomes attributed to 20‐HETE in vitro and in vivo (Garcia et al, Circ. Res., 2017). To further establish the role of GPR75 as a 20‐HETE target for its bioactions, global GPR75 knockout (Gpr75−/−) mice were generated. A breeding colony of Gpr75+/−XGpr75+/− has been established and experiments were conducted to assert the genotype and assess whether a basic phenotype exists. Levels GPR75 mRNA were undetectable in brain, liver, heart, aorta and kidney from Gpr75−/− mice. Levels of Gpr75 mRNA in liver, heart and aorta tissues from Gpr75+/− (HET) was lower compared to littermate Gpr75+/+ (WT) mice. The initial phenotypic characterization showed no differences between WT and transgenic mice in body weight or systolic blood pressure (93±4, 89±5 and 88±6 mmHg in male and female WT, Gpr75+/− and Gpr75−/− mice, respectively). There were no significant gender differences in body weight or blood pressure. Since 20‐HETE has been shown to promote vasoconstriction, increase vascular reactivity and contribute to the myogenic response in renal and cerebral microvessels, we assessed whether deficiencies in GPR75 affects myogenic response in preglomerular arterioles (~50–80 μm). The myogenic response was markedly impaired in arteries from Gpr75−/− mice as internal diameter increased in response to increasing pressure and in response to 100 mmHg, internal diameter of arteries from Gpr75−/− and Gpr75+/− mice was 119.5±1.22 and 101.7±3.1 μm, respectively, as compared to 80.3±3.4 μm in arteries from WT (p<0.05). These results, together with our finding that in vascular smooth muscle cells 20‐HETE‐GPR75 pairing leads to inhibition of the BKca channels and increases in intracellular calcium concentration which contribute to vasoconstriction, suggest that deficiency in the expression of GPR75 mediates the impaired myogenic response because 20‐HETE is lacking its cellular target.Support or Funding InformationSupported by NIH grant HL139793 and Regeneron Pharmaceuticals Inc.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Impact of APOL1 on Chronic Kidney Disease and Hypertension.

Essential hypertension is a clinical diagnosis based on the presence of an elevated systemic blood pressure on physical examination without a clear inciting cause. It has multiple etiologies and is not a homogeneous disorder. Hypertension contributes to the development and progression of atherosclerotic cardiovascular diseases, and antihypertensive treatment reduces the risk of fatal and nonfatal myocardial infarction, stroke, and congestive heart failure. Although hypertension is frequently present in nondiabetic individuals with low levels of proteinuria and chronic kidney disease, reducing blood pressures in this population does not reliably slow nephropathy progression. Many of these patients with recent African ancestry have the primary kidney disease "solidified glomerulosclerosis" that is strongly associated with renal-risk variants in the apolipoprotein L1 gene (APOL1). This kidney disease contributes to secondarily elevated blood pressures. The APOL1-associated spectrum of nondiabetic nephropathy also includes proteinuric kidney diseases, idiopathic focal segmental glomerulosclerosis, collapsing glomerulopathy, severe lupus nephritis, and sickle cell nephropathy. This article reviews relationships between mild to moderate essential hypertension and chronic kidney disease with a focus on the role of APOL1 in development of hypertension. Available evidence strongly supports that APOL1 renal-risk variants associate with glomerulosclerosis in African Americans, which then causes secondary hypertension, not with essential hypertension per se.

Mathematical model of hemodynamic mechanisms and consequences of glomerular hypertension in diabetic mice

Many preclinically promising therapies for diabetic kidney disease fail to provide efficacy in humans, reflecting limited quantitative translational understanding between rodent models and human disease. To quantitatively bridge interspecies differences, we adapted a mathematical model of renal function from human to mice, and incorporated adaptive and pathological mechanisms of diabetes and nephrectomy to describe experimentally observed changes in glomerular filtration rate (GFR) and proteinuria in db/db and db/db UNX (uninephrectomy) mouse models. Changing a small number of parameters, the model reproduced interspecies differences in renal function. Accounting for glucose and Na+ reabsorption through sodium glucose cotransporter 2 (SGLT2), increasing blood glucose and Na+ intake from normal to db/db levels mathematically reproduced glomerular hyperfiltration observed experimentally in db/db mice. This resulted from increased proximal tubule sodium reabsorption, which elevated glomerular capillary hydrostatic pressure (Pgc) in order to restore sodium balance through increased GFR. Incorporating adaptive and injurious effects of elevated Pgc, we showed that preglomerular arteriole hypertrophy allowed more direct transmission of pressure to the glomerulus with a smaller mean arterial pressure rise; Glomerular hypertrophy allowed a higher GFR for a given Pgc; and Pgc-driven glomerulosclerosis and nephron loss reduced GFR over time, while further increasing Pgc and causing moderate proteinuria, in agreement with experimental data. UNX imposed on diabetes increased Pgc further, causing faster GFR decline and extensive proteinuria, also in agreement with experimental data. The model provides a mechanistic explanation for hyperfiltration and proteinuria progression that will facilitate translation of efficacy for novel therapies from mouse models to human.

PP.22.06] PLASMA D-DIMER LEVELS ARE RELATED TO INTRARENAL VASCULAR RESISTANCE IN NON-DIABETIC ESSENTIAL HYPERTENSIVE PATIENTS

Objective: Hypertensive nephroangiosclerosis is characterized by progressive narrowing of preglomerular arterioles that leads to increased intrarenal vascular resistance. This can be estimated by duplex ultrasound evaluation and measurement of the intrarenal resistance index (IR). In addition to high blood pressure, other factors can contribute to development and progression of nephroangiosclerosis. The aim of this study was to investigate the possible relationships between some emergent cardiovascular risk factors, such as a prothrombotic state, and presence and severity of nephroangiosclerosis, as evaluated by measurement of IR, in hypertension. Design and method: In 115 non-diabetic, essential hypertensive patients (age 46 ± 13 years; 63 males, 57 never treated with anti-hypertensive drugs, 58 studied after drug wash-out of at least 2 weeks) we measured anthropometric variables, fasting plasma glucose and insulin, HOMA-index, 24-h creatinine clearance (CrCl) and urinary protein excretion, plasma levels of fibrinogen, D-dimer, prothrombin fragment 1 + 2, plasminogen activator inhibitor-1, tissue-plasminogen activator, lipoproteina (a), and homocysteine. Patients with CrCl < 30 ml/min/1.73 m2 were excluded. In all patients, IR was calculated as the average of 4 to 6 separate measurements that were obtained in the interlobar arteries respectively in the upper, middle, and lower third of both kidneys and patients were subdivided according to tertiles of IR. Results: IR was greater in women than in men, and in patients previously treated with antihypertensive drugs. Patients in the highest tertile of IR were older and had greater body mass index, pulse pressure, D-dimer and fibrinogen levels, and lower CrCl than patients in lowest IR tertile. No differences in the other variables considered in the study were found across IR tertiles. At univariate analysis IR was significantly and directly related to age, systolic and pulse pressure, HOMA-index, urinary protein excretion, D-dimer, and inversely with CrCl. At multivariate analysis, IR was independently associated with pulse pressure, CrCl and D-dimer levels. Conclusions: In non-diabetic hypertensive patients subclinical damage of intrarenal vessels is related with an activation of the hemostatic system that could play a role in the early stages of hypertensive nephropathy.

Increased hydrogen peroxide impairs angiotensin II contractions of afferent arterioles in mice after renal ischaemia-reperfusion injury.

Renal ischaemia-reperfusion injury (IRI) increases angiotensin II (Ang II) and reactive oxygen species (ROS) that are potent modulators of vascular function. However, the roles of individual ROS and their interaction with Ang II are not clear. Here we tested the hypothesis that IRI modulates renal afferent arteriolar responses to Ang II via increasing superoxide (O2-) or hydrogen peroxide (H2 O2 ). Renal afferent arterioles were isolated and perfused from C57BL/6 mice 24h after IRI or sham surgery. Responses to Ang II or noradrenaline were assessed by measuring arteriolar diameter. Production of H2 O2 and O2- was assessed in afferent arterioles and renal cortex. Activity of SOD and catalase, and mRNA expressions of Ang II receptors were assessed in pre-glomerular arterioles and renal cortex. Afferent arterioles from mice after IRI had a reduced maximal contraction to Ang II (-27±2 vs. -42±1%, P<0.001), but retained a normal contraction to noradrenaline. Arterioles after IRI had a 38% increase in H2 O2 (P<0.001) and a 45% decrease in catalase activity (P<0.01). Contractions were reduced in normal arterioles after incubation with H2 O2 (-22±2 vs. -42±1%, P<0.05) similar to the effects of IRI. However, the impaired contractions were normalized by incubation with PEG catalase despite a reduced AT1 R expression. Renal IRI in mice selectively impairs afferent arteriolar responses to Ang II because of H2 O2 accumulation that is caused by a reduced catalase activity. This could serve to buffer the effect of Ang II after IRI and may be a protective mechanism.

P66Shc regulates renal vascular tone in hypertension-induced nephropathy.

Renal preglomerular arterioles regulate vascular tone to ensure a large pressure gradient over short distances, a function that is extremely important for maintaining renal microcirculation. Regulation of renal microvascular tone is impaired in salt-sensitive (SS) hypertension-induced nephropathy, but the molecular mechanisms contributing to this impairment remain elusive. Here, we assessed the contribution of the SH2 adaptor protein p66Shc (encoded by Shc1) in regulating renal vascular tone and the development of renal vascular dysfunction associated with hypertension-induced nephropathy. We generated a panel of mutant rat strains in which specific modifications of Shc1 were introduced into the Dahl SS rats. In SS rats, overexpression of p66Shc was linked to increased renal damage. Conversely, deletion of p66Shc from these rats restored the myogenic responsiveness of renal preglomerular arterioles ex vivo and promoted cellular contraction in primary vascular smooth muscle cells (SMCs) that were isolated from renal vessels. In primary SMCs, p66Shc restricted the activation of transient receptor potential cation channels to attenuate cytosolic Ca2+ influx, implicating a mechanism by which overexpression of p66Shc impairs renal vascular reactivity. These results establish the adaptor protein p66Shc as a regulator of renal vascular tone and a driver of impaired renal vascular function in hypertension-induced nephropathy.

Conduction of feedback-mediated signal in a computational model of coupled nephrons.

The nephron in the kidney regulates its fluid flow by several autoregulatory mechanisms. Two primary mechanisms are the myogenic response and the tubuloglomerular feedback (TGF). The myogenic response is a property of the pre-glomerular vasculature in which a rise in intravascular pressure elicits vasoconstriction that generates a compensatory increase in vascular resistance. TGF is a negative feedback response that balances glomerular filtration with tubular reabsorptive capacity. While each nephron has its own autoregulatory response, the responses of the kidney's many nephrons do not act autonomously but are instead coupled through the pre-glomerular vasculature. To better understand the conduction of these signals along the pre-glomerular arterioles and the impacts of internephron coupling on nephron flow dynamics, we developed a mathematical model of renal haemodynamics of two neighbouring nephrons that are coupled in that their afferent arterioles arise from a common cortical radial artery. Simulations were conducted to estimate internephron coupling strength, determine its dependence on vascular properties and to investigate the effect of coupling on TGF-mediated flow oscillations. Simulation results suggest that reduced gap-junctional conductances may yield stronger internephron TGF coupling and highly irregular TGF-mediated oscillations in nephron dynamics, both of which experimentally have been associated with hypertensive rats.

Expression of (pro)renin receptor and its upregulation by high salt intake in the rat nephron

A functional receptor for renin and prorenin ((P)RR) was identified as a new component of the renin–angiotensin system. The precise localization of (P)RR in the kidney has not been clarified. The present study was designed to determine the localization of (P)RR in the rat nephron and to investigate the regulation of renal (P)RR expression by high salt (HS) intake. (P)RR mRNA levels in the kidney sections and isolated nephron segments were examined using reverse transcription and polymerase chain reaction (RT-PCR), and (P)RR protein levels were examined by immunoblot and immunohistochemical analyses. Renal (P)RR mRNA and protein levels in rats fed a HS diet for 4 weeks were also compared with those fed a normal salt diet. (P)RR mRNA was expressed in various nephron segments of the cortex and medulla; glomeruli (Glm), proximal tubules (PT), thick ascending limbs (TAL) and collecting ducts (CD). (P)RR protein was highly expressed in the PT, medullary TAL (MTAL) and inner medullary CD (IMCD), and lowly in the preglomerular arterioles (Art) and Glm. HS intake increased (P)RR protein levels in the Glm, PT and tubules of medullary rays. These results indicated that (P)RR is expressed throughout various nephron segments and Art, and that (P)RR protein is expressed predominantly in the PT, MTAL and IMCD. HS intake appears to upregulate the (P)RR expression in the Glm, PT and tubules of medullary rays, suggesting that (P)RR may be involved in the regulation of renal function and HS-induced disorders.

Large Blood Pressure Variability Aggravates Arteriolosclerosis and Cortical Sclerotic Changes in the Kidney in Hypertensive Rats

It has been shown that increased short-term blood pressure (BP) variability (BPV) aggravates hypertensive cardiac remodeling in spontaneously hypertensive rats (SHRs) through a cardiac angiotensin II (angII) system. However, little was known about the renal damage induced by large BPV. Thus, histological changes in the kidney were investigated and candesartan, an angII type 1 receptor blocker (ARB), was also examined to see whether it would prevent renal damage in SHRs with large BPV. METHODS AND RESULTS: Bilateral sinoaortic denervation (SAD) was performed in SHRs to create a model of a combination of hypertension and large BPV. SAD increased BPV without changing mean BP. Seven weeks later, SAD induced patchy, wedge-shaped, focal sclerotic lesions accompanied by interstitial fibrosis and ischemic changes of glomeruli and tubules in the cortex. The pre-glomerular arterioles adjacent to the sclerotic lesions showed arteriolosclerotic changes associated with vascular smooth muscle cell proliferation and extracellular matrix deposition, leading to the luminal narrowing and occlusion. Chronic treatment with a subdepressor dose of candesartan prevented not only arteriolosclerotic changes but also cortical sclerotic lesions in SHRs with SAD without changing BPV. Large BPV aggravates pre-glomerular arteriolosclerosis, which results in the cortical sclerotic changes in SHRs through a local angII-mediated mechanism. This study raised the possibility that ARB is useful for renal protection in patients who have a combination of hypertension and increased BPV.

Role of cytochrome P450 epoxygenase in regulating renal membrane transport and hypertension

Cytochrome P450 (CYP)-epoxygenase is highly expressed in the kidney and its metabolism of arachidonic acid plays important roles in regulating renal Na transport and in modulating vasoactivity in the kidney. In the past several years, progress has been made not only in characterizing the specific CYP-epoxygenases responsible for the regulation of membrane transport and vasoactivity in the kidney but also in exploring the mechanism by which they regulate renal Na transport and vasodilation of preglomerular arterioles. This review summarizes and updates recent progress in this area of research. CYP-epoxygenase metabolites of arachidonic acid inhibit epithelial Na channel (ENaC) in the cortical collecting duct (CCD), and 11,12-epoxyeicosatrienoic acid (11,12-EET) is mainly responsible for mediating the inhibitory effect on ENaC. Downregulation of CYP2C44 abolishes arachidonic acid mediated inhibition of ENaC and increases ENaC activity. In addition, 11,12-EET stimulates Ca-activated big conductance K channels in the CCD and afferent arterioles smooth muscles. Activation of big conductance K channels by 11,12-EET is responsible for EET-induced vasodilation in preglomerular arterioles. 11,12-EET-induced vasodilation is absent in preglomerular arterioles pretreated with okadaic acid. CYP-epoxygenase mediated suppression of renal Na transport is partially achieved by inhibition of ENaC activity in the CCD and CYP2C44-derived EETs are responsible for inhibition of ENaC. Stimulation of serine/threonine protein phosphatase 2A (PP2A) contributes to 11,12-EET-induced activation of big conductance K channels and vasodilation in preglomerular arterioles.

Abstract 376: The Expression of (pro)renin Receptor is Upregulated in the Kidney by High Salt Diet and No Inhibition

The (pro)renin receptor ((P)RR)-bound (pro)renin not only causes the generation of angiotensin II via the increased enzymatic activity, it also activates the receptor’s own intracellular signaling pathways up-regulating the expression of the profibrotic proteins. To clarify the regulation of (P)RR expression, the present study examined the effects of high salt diet and nitric oxide synthase (NOS) inhibition on the (P)RR expression in the kidney. The nephron segments were isolated from male Sprague-Dawley (SD) rats by microdissection and bulk isolation technique, and the (P)RR mRNA and protein expressions were examined by using reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis. In adiition, 5 week-old, male SD rats were randomly divided into 3 groups: a control group, a high salt diet (HS) group and a Nω-Nitro-L-arginine (L-NAME) group, and each group was treated with vehicle, high salt diet (8%, NaCl), or L-NAME (600mg/ml in drinking water), respectively. After 4 weeks, the (P)RR expression in the kidney was compared among these groups. The (P)RR mRNA was expressed in the glomerulus (Glm), the proximal convoluted and straight tubule, the cortical and medullary thick ascending limb (TAL) and collecting duct. The (P)RR protein as well as mRNA was expressed widely in the nephron segments; the preglomerular arteriole, the Glm, the proximal tubules (PT), the medullary TAL (mTAL) and inner medullary collecting duct (IMCD). Compared with the control group, the (P)RR protein levels significantly increased in the kidney cortex of both HS group and L-NAME group by 96% (p&lt;0.01) and 506% (p&lt;0.01) and in the inner medulla of L-NAME group by 148% (p&lt;0.05), but did not significantly change in the outer medulla of HS group or L-NAME group. HS increased the (P)RR protein levels in the Glm and PT by 48% (p&lt;0.05) and 39% (p&lt;0.01), but did not affect them in other nephron segments. These results indicated that (P)RR is expressed widely in the nephron segments and that HS and NOS inhibition upregulate the (P)RR expression in the kidney, suggesting roles of (P)RR in hypertensive kidney disorder.

Chronic treatment with angiotensin‐(1‐7) improves renal endothelial dysfunction in apolipoproteinE‐deficient mice

ApolipoproteinE-deficient [apoE (-/-)] mice, a model of human atherosclerosis, develop endothelial dysfunction caused by decreased levels of nitric oxide (NO). The endogenous peptide, angiotensin-(1-7) [Ang-(1-7)], acting through its specific GPCR, the Mas receptor, has endothelium-dependent vasodilator properties. Here we have investigated if chronic treatment with Ang-(1-7) improved endothelial dysfunction in apoE (-/-) mice. ApoE (-/-) mice fed on a lipid-rich Western diet were divided into three groups and treated via osmotic minipumps with either saline, Ang-(1-7) (82 µg·kg(-1) ·h(-1) ) or the same dose of Ang-(1-7) together with D-Ala-Ang-(1-7) (125 µg·kg(-1) ·h(-1) ) for 6 weeks. Renal vascular function was assessed in isolated perfused kidneys. Ang-(1-7)-treated apoE (-/-) mice showed improved renal endothelium-dependent vasorelaxation induced by carbachol and increased renal basal cGMP production, compared with untreated apoE (-/-) mice. Tempol, a reactive oxygen species (ROS) scavenger, improved endothelium-dependent vasorelaxation in kidneys of saline-treated apoE (-/-) mice whereas no effect was observed in Ang-(1-7)-treated mice. Chronic treatment with D-Ala-Ang-(1-7), a specific Mas receptor antagonist, abolished the beneficial effects of Ang-(1-7) on endothelium-dependent vasorelaxation. Renal endothelium-independent vasorelaxation showed no differences between treated and untreated mice. ROS production and expression levels of the NAD(P)H oxidase subunits gp91phox and p47phox were reduced in isolated preglomerular arterioles of Ang-(1-7)-treated mice, compared with untreated mice, whereas eNOS expression was increased. Chronic infusion of Ang-(1-7) improved renal endothelial function via Mas receptors, in an experimental model of human cardiovascular disease, by increasing levels of endogenous NO.

The contribution of endogenous vasodilators to the control of glomerular hemodynamics

Preglomerular afferent (Af-) and postglomerular efferent arterioles (Ef-Arts) are crucial vascular segments in the control of glomerular hemodynamics. However, their vascular reactivity is not fully understood. We examined: 1) their responses to angiotensin II (AII) or norepinephrine (NE), and 2) the possible modulatory roles of nitric oxide (NO) and prostaglandins (PGs) in these responses. Rabbit Af- or Ef-Arts were microperfused in vitro. Ef-Arts were perfused in either the orthograde direction from the distal end of Af-Arts through the glomerulus (OP) or the retrograde direction from its distal end to eliminate the influence of the glomerulus (RP). Although AII and NE constricted both arterioles in a dose-dependent manner, sensitivity to AII was higher in Ef-Arts. AII began to cause significant (P < 0.01) constriction from 10(-9) M (11 +/- 3%, n = 11) in Af-Arts, and from 10(-11) M in Ef-Arts (OP; 11 +/- 4%, n = 9. RP; 10 +/- 2%, n = 5). In addition, both AII and NE produced stronger constriction of Ef-Arts in RP than OP; AII at 10(-8) M or NE at 10(-6) M decreased the diameter by 35 +/- 4% or 25 +/- 4% in OP and 74 +/- 4% or 62 +/- 7% in RP. NO synthesis inhibitor nitro-L-arginine (L-NAME; 10(-4) M) increased the sensitivity of Af-Art to AII without affecting the reactivity of Ef-Art; in L-NAME-pretreated Af-Arts, AII began to cause significant constriction from 10(-10) M (14 +/- 4%, n = 9, P < 0.01). Thus, L-NAME-pretreatment significantly decreased the differences in sensitivity to AII between Af- and Ef-Arts without affecting different vascular responses between OP and RP. Indomethacin (5 x 10(-5) M) significantly augmented the AII- or NE-induced Ef-Art constriction only in OP; AII at 10(-8) M or NE at 10(-6) M decreased the diameter by 72 +/- 5% (n = 8) or 48 +/- 3% (n = 7). Thus, indomethacin-pretreatment markedly diminished the differences in responses between OP and RP. These results suggest that 1) NO modulates AII action only in the Af-Art, contributing to the difference in sensitivity to AII between Af- and Ef-Art, and 2) the glomerulus controls vascular reactivity of the downstream Ef-Art by releasing PGs.

Angiotensin II Type 1A Receptors in Vascular Smooth Muscle Cells Do Not Influence Aortic Remodeling in Hypertension

Vascular injury and remodeling are common pathological sequelae of hypertension. Previous studies have suggested that the renin-angiotensin system acting through the type 1 angiotensin II (AT(1)) receptor promotes vascular pathology in hypertension. To study the role of AT(1) receptors in this process, we generated mice with cell-specific deletion of AT(1) receptors in vascular smooth muscle cells using Cre/Loxp technology. We crossed the SM22α-Cre transgenic mouse line expressing Cre recombinase in smooth muscle cells with a mouse line bearing a conditional allele of the Agtr1a gene (Agtr1a (flox)), encoding the major murine AT(1) receptor isoform (AT(1A)). In SM22α-Cre(+)Agtr1a (flox/flox) (SMKO) mice, AT(1A) receptors were efficiently deleted from vascular smooth muscle cells in larger vessels but not from resistance vessels such as preglomerular arterioles. Thus, vasoconstrictor responses to angiotensin II were preserved in SMKO mice. To induce hypertensive vascular remodeling, mice were continuously infused with angiotensin II for 4 weeks. During infusion of angiotensin II, blood pressures increased significantly and to a similar extent in SMKO and control mice. In control mice, there was evidence of vascular oxidative stress indicated by enhanced nitrated tyrosine residues in segments of aorta; this was significantly attenuated in SMKO mice. Despite these differences in oxidative stress, the extent of aortic medial expansion induced by angiotensin II infusion was virtually identical in both groups. Thus, vascular AT(1A) receptors promote oxidative stress in the aortic wall but are not required for remodeling in angiotensin II-dependent hypertension.

Connexin abundance in resistance vessels from the renal microcirculation in normo- and hypertensive rats

The expression of connexins in renal arterioles is believed to have a profound impact on conducted responses, regulation of arteriolar tonus and renal blood flow. We have previously shown that in renal preglomerular arterioles, conducted vasomotor responses are 40% greater in spontaneously hypertensive rats (SHR) than in normotensive Sprague–Dawley (SD) rats. Because conducted vasomotor responses depend on the cell–cell communication mediated through gap junctions, we hypothesized that the increased magnitude of conducted vasomotor response in SHR is associated with an increased amount of connexins in renal arterioles. To test this hypothesis, the amount of connexin 37 (Cx37), Cx40 and Cx43 was assessed in renal arterioles from normo- and hypertensive rats using quantitative immunofluorescence laser confocal miscroscopy. To account for differences in genetic background, we included both normotensive Wistar–Kyoto (WKY) and SD rats in the study. In all three strains of rats, and for all three isoforms, the expression of connexins was predominantly confined to the endothelial cells. We found a significantly increased abundance (240 ± 17.6%, p<0.05) of Cx37 in arterioles from WKY compared with SD and SHR. This high abundance of Cx37 was not related to blood pressure because normotensive SD demonstrated a level of Cx37 similar to that of SHR. Additionally, we found no evidence for an increased abundance of Cx40 and Cx43 in renal arterioles of SHR when compared with normotensive counterparts.

Calcium antagonists: current and future applications based on new evidence. Renal protective action of calcium channel blockers

Ca channel blockers have been widely prescribed as an antihypertensive agent in Japan, because the blood pressure (BP) lowering effect of it is strong among Japanese patients whose amount of salt intake is high and patients with chronic kidney disease (CKD) whose sodium sensitivity of BP is enhanced. In addition, it can maintain the perfusion pressure into important organs including kidneys despite lowered systemic BP, and can be used efficiently in combinations with many types of antihypertensive agents. On the other hand, most of Ca channel blockers dilate mainly preglomerular afferent arterioles, resulting in elevated glomerular capillary pressure. Therefore, renal protection by Ca channel blockers remains in debate. We will discuss the renal protective action of new Ca channel blockers, which can dilate postglomerular efferent arterioles.