Angiotensin II-dependent Hypertension Research Articles

Inhibition of soluble epoxide hydrolase by cis-4-[4-(3-adamantan-1-ylureido)cyclohexyl-oxy]benzoic acid exhibits antihypertensive and cardioprotective actions in transgenic rats with angiotensin II-dependent hypertension

The present study was undertaken to evaluate the effects of chronic treatment with c-AUCB {cis-4-[4-(3-adamantan-1-ylureido)cyclohexyl-oxy]benzoic acid}, a novel inhibitor of sEH (soluble epoxide hydrolase), which is responsible for the conversion of biologically active EETs (epoxyeicosatrienoic acids) into biologically inactive DHETEs (dihydroxyeicosatrienoic acids), on BP (blood pressure) and myocardial infarct size in male heterozygous TGR (Ren-2 renin transgenic rats) with established hypertension. Normotensive HanSD (Hannover Sprague-Dawley) rats served as controls. Myocardial ischaemia was induced by coronary artery occlusion. Systolic BP was measured in conscious animals by tail plethysmography. c-AUCB was administrated in drinking water. Renal and myocardial concentrations of EETs and DHETEs served as markers of internal production of epoxygenase metabolites. Chronic treatment with c-AUCB, which resulted in significant increases in the availability of biologically active epoxygenase metabolites in TGR (assessed as the ratio of EETs to DHETEs), was accompanied by a significant reduction in BP and a significantly reduced infarct size in TGR as compared with untreated TGR. The cardioprotective action of c-AUCB treatment was completely prevented by acute administration of a selective EETs antagonist [14,15-epoxyeicosa-5(Z)-enoic acid], supporting the notion that the improved cardiac ischaemic tolerance conferred by sEH inhibition is mediated by EETs actions at the cellular level. These findings indicate that chronic inhibition of sEH exhibits antihypertensive and cardioprotective actions in this transgenic model of angiotensin II-dependent hypertension.

RhoA guanine exchange factor expression profile in arteries: evidence for a Rho kinase-dependent negative feedback in angiotensin II-dependent hypertension

Sustained overactivation of RhoA is a common component for the pathogenesis of several cardiovascular disorders, including hypertension. Although activity of Rho proteins depends on Rho exchange factors (Rho-GEFs), the identity of Rho-GEFs expressed in vascular smooth muscle cells (VSMC) and participating in the control of Rho protein activity and Rho-dependent functions remains unknown. To address this question, we analyzed by quantitative RT-PCR the expression profile of 28 RhoA-GEFs in arteries of normotensive (saline-treated) and hypertensive (ANG II-treated) rats. Sixteen RhoA-GEFs were downregulated in mesenteric arteries of hypertensive rats, among which nine are also downregulated in cultured VSMC stimulated by ANG II (100 nM, 48 h), suggesting a direct effect of ANG II. Inhibition of type 1 ANG II receptors (losartan, 1 μM) or Rho kinase (fasudil, 10 μM) prevented ANG II-induced RhoA-GEF downregulation. Functionally, ANG II-induced downregulation of RhoA-GEFs is associated with decreased Rho kinase activation in response to endothelin-1, norepinephrine, and U-46619. This work thus identifies a group of RhoA-GEFs that controls RhoA and RhoA-dependent functions in VSMC, and a negative feedback of RhoA/Rho kinase activity on the expression of these RhoA-GEFs that may play an adaptative role to limit RhoA/Rho kinase activation.

Cardiac-Autonomic Imbalance and Baroreflex Dysfunction in the Renovascular Angiotensin-Dependent Hypertensive Mouse

Mouse models provide powerful tools for studying the mechanisms underlying the dysfunction of the autonomic reflex control of cardiovascular function and those involved in cardiovascular diseases. The established murine model of two-kidney, one-clip (2K1C) angiotensin II-dependent hypertension represents a useful tool for studying the neural control of cardiovascular function. In this paper, we discuss the main contributions from our laboratory and others regarding cardiac-autonomic imbalance and baroreflex dysfunction. We show recent data from the angiotensin-dependent hypertensive mouse demonstrating DNA damage and oxidative stress using the comet assay and flow cytometry, respectively. Finally, we highlight the relationships between angiotensin and peripheral and central nervous system areas of cardiovascular control and oxidative stress in the 2K1C hypertensive mouse.

Renal functional responses to selective intrarenal renin inhibition in Cyp1a1-Ren2 transgenic rats with ANG II-dependent malignant hypertension

Angiotensin (ANG) II-dependent hypertension is characterized by increases in intrarenal ANG II levels, derangement in renal hemodynamics, and augmented tubular sodium reabsorptive capability. Increased nephron expression of renin-angiotensin system components, such as angiotensinogen by proximal tubule cells and renin by collecting duct principal cells, has been associated with an augmented ability of the kidney to form ANG II in hypertensive states. However, the contribution of de novo intrarenal ANG II production to the development and maintenance of ANG II-dependent hypertension remains unclear. The present study was performed to determine the effects of selective intrarenal renin inhibition on whole kidney hemodynamics and renal excretory function in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension in the absence of the confounding influence of associated reductions in mean arterial pressure (MAP). Male Cyp1a1-Ren2 transgenic rats were induced to develop malignant hypertension, anesthetized, and surgically prepared for intrarenal administration of the direct renin inhibitor aliskiren (0.01 mg/kg). Following acute aliskiren treatment, urine flow and sodium excretion increased (10.5 ± 1.1 to 15.9 ± 1.9 μl/min, P < 0.001; 550 ± 160 to 1,370 ± 320 neq/min, P < 0.001, respectively) and ANG II excretion decreased (120 ± 30 to 63 ± 17 fmol/h, P < 0.05). There were no significant changes in MAP, glomerular filtration rate, estimated renal plasma flow, plasma ANG II levels, or protein excretion. The present findings demonstrate that selective renal renin inhibition elicits diuretic and natriuretic responses in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension. Elevated intraluminal ANG II levels likely act to augment tubular reabsorptive function and, thereby, contribute to the elevated blood pressure in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension.

Direct Renin Inhibition With Aliskiren Normalizes Blood Pressure in Cyp1a1-Ren2 Transgenic Rats With Inducible Angiotensin II-Dependent Malignant Hypertension

IntroductionCyp1a1-Ren2 transgenic rats [strain name: TGR(Cyp1a1Ren2)], administered indole-3-carbinol (I3C) develop angiotensin (ANG) II-dependent hypertension due to hepatic expression of the Ren2 renin gene. Although AT1 receptor blockade prevents the development of hypertension and normalizes the elevated arterial blood pressure of Cyp1-Ren2 rats, little information is available regarding the blood pressure and renal functional responses to direct inhibition of renin in this high circulating renin model of ANG II-dependent hypertension. This study was performed to determine the effects of acute direct renin inhibition with aliskiren on blood pressure and renal hemodynamics in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension. MethodsMean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital- anesthetized male Cyp1a1-Ren2 rats during control conditions and after administration of the renin inhibitor, aliskiren (10 mg/kg, intravenous) ResultsRats induced with I3C had higher MAP (194 ± 7 versus 141 ± 2 mm Hg, P < 0.001), lower renal plasma flow (RPF; 2.47 ± 0.23 versus 4.17 ± 0.35 mL/min/g, P < 0.001) and lower glomerular filtration rate (GFR; 1.01 ± 0.07 versus 1.34 ± 0.06 mL/min/g, P = 0.01) than noninduced Cyp1a1-Ren2 rats (n = 5). Aliskiren administration decreased MAP (194 ± 7to136 ± 2 mm Hg, P < 0.001) and increased RPF (2.47 ±0.23 versus 4.31 ± 0.20 mL/min/g, P < 0.001) in hypertensive but not in normotensive rats, without altering GFR. ConclusionsAcute renin inhibition with aliskiren normalizes MAP and RPF in Cyp1a1-Ren2 rats with malignant hypertension. The normalization of MAP and RPF after acute renin inhibition indicates that renin generated by expression of the Ren2 gene is responsible for the maintenance of malignant hypertension and the associated reduction in renal hemodynamic function in Cyp1a1-Ren2 rats.

Endothelin-1 (ET-1) modulates epithelial-mesenchymal transition (EMT), which contributes to kidney tubulo-interstitial fibrosis in angiotensin II-dependent hypertension

The origin of myofibroblasts remains uncertain, but studies suggest that the epithelial cells may acquire a fibroblast-like phenotype via epithelial-mesenchymal transition (EMT). Objective of the study was to investigate whether EMT may contribute to the development of kidney fibrosis in a model of angiotensin II-dependent hypertension and to identify the role of ET-1 via ETA/ETB receptors. Transgenic rats TGRen2 (n=35) received for 4 weeks one of the following treatments a) irbesartan, b) bosentan, non selective ETA /ETB receptor antagonist, c) BMS-182874, selective ETA,antagonist, d) BMS+irbesartan, e) placebo. EMT was assessed by investigating coexpression of a marker of epithelial cell (E-cadherin) and one of myofibroblast (S100A4 or alfa-SMA) with double immunofluorescence. Specific immunoreactivity was measured using QWinStandard Leica ImageTMsoftware. A reduction in blood pressure was found only with irbesartan, whereas both bosentan and irbesartan significantly lowered tubulo-interstitial fibrosis. Coexpression of E-cadherin and S100A4, or E-cadherin and alfa-SMA, markedly decreased in the tubular cells of TGRen2 treated with irbesartan or bosentan. Alfa-SMA expression decreased after irbesartan, bosentan and BMS+irbesartan, but not after BMS. S100A4 expression was reduced after irbesartan, bosentan and BMS+irbesartan. E-cadherin increased only after irbesartan. Coexpression of the markers of myofibroblasts and kidney epithelial cells, by demonstrating the development of EMT during the onset of kidney hypertension-induced damage, suggests a crucial role of EMT in the pathogenesis of Ang II-mediated fibrosis. The reduction of myofibroblast markers not only after irbesartan, but also after blockade of ETA/ETB receptors, suggests an involvement of ET-1 in the development of Ang II-mediated EMT.

Renal mechanisms contributing to the antihypertensive action of soluble epoxide hydrolase inhibition in Ren-2 transgenic rats with inducible hypertension.

In the present study, we examined the effects of soluble epoxide hydrolase (sEH) inhibition on the development of angiotensin II-dependent hypertension and on renal function in transgenic rats with inducible expression of the mouse renin gene (strain name Cyp1a1-Ren-2). Hypertension was induced in these rats by indole-3-carbinol (I3C; 0.3% in the diet) for 12 days. The sEH inhibitor cis-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (c-AUCB) was given in two doses (13 or 26 mg l-1) in drinking water. Blood pressure (BP), body weight (BW) and renal excretory parameters were monitored in conscious animals during the experiment. Renal haemodynamics was assessed at the end of treatment in anaesthetized rats. I3C administration resulted in severe hypertension with a rise in systolic BP from 118 ± 2 to 202 ± 3 mmHg, a loss of BW from 266 ± 5 to 228 ± 4 g and a rise in proteinuria from 14 ± 2 to 34 ± 3 mg day-1. Both doses of c-AUCB significantly attenuated the development of hypertension (systolic BP of 181 ± 4 and 176 ± 4 mmHg, respectively), the loss in BW (256 ± 4 and 259 ± 3 g, respectively) and the degree of proteinuria (27 ± 2 and 25 ± 3 mg day-1, respectively) to a similar extent. Moreover, c-AUCB prevented the reduction in renal plasma flow (5.4 ± 0.4 vs. 4.6 ± 0.3 ml min-1 g-1) and significantly increased sodium excretion (0.84 ± 0.16 vs. 0.38 ± 0.08 μmol min-1 g-1) during I3C administration. These data suggest that the oral administration of c-AUCB displays antihypertensive effects in Ren-2 transgenic rats with inducible malignant hypertension via an improvement of renal function.

Counterpoint: Activation of the Intrarenal Renin-Angiotensin System is the Dominant Contributor to Systemic Hypertension

Our discussion regarding the dominant mechanism responsible for hypertension calls to mind the famous poem, “The Blind Men and the Elephant,” by John Godfrey Saxe based on an ancient fable from India. In essence, the blind men described the elephant based on their specific encounter, thus

Reactive Oxygen Species, NADPH Oxidases, and Hypertension

Reactive oxygen species (ROS) produced in the neuronal, renal, and vascular systems not only influence cardiovascular physiology but are also strongly implicated in pathological signaling leading to hypertension. Different sources of ROS have been identified, ranging from xanthine-xanthine oxidase and mitochondria to NADPH oxidase (Nox) enzymes. Of 7 Nox family members, Nox1, Nox2, and Nox4 (and Nox5 in humans) influence the cardiovascular system. Their activation processes and cell and tissue distribution vary widely, adding complexity to understanding their functional roles. Whether these systems act collectively or independently in disease conditions is unclear, but recently feed forward mechanisms have been established between ROS sources. Studies published in Hypertension over the last few years are the focus of this review, and they provide a framework with which to consider the roles of Nox enzymes in neuronal, renal, and vascular hypertensive mechanisms, as well as cardiac remodeling, and their relationships with other ROS-generating systems. ### Neuronal ROS in Hypertension Redox signaling in the central nervous system is well recognized in neuronal control of blood pressure (BP), as well as in response to angiotensin II (Ang II) and aldosterone, which are linked to ROS-dependent hypertension. Recently, new roles for ROS have been described in the hypothalamus and brain stem, nucleus tractus solitarius (NTS), subfornical organ (SFO), rostral ventrolateral medulla, and area postrema (Figure 1). Figure 1. Neuronal NADPH oxidase–dependent ROS involved in central regulation of hypertension. NADPH oxidase homologues, mainly Nox2 and Nox4, are found in different regions of the neuronal system and are reported to have a role in the neuropathogenesis of hypertension by enhancing the sympathetic nerve activity. Nox-induced ROS initiate a forward loop in cross-activation of different receptors and between Nox and mitochondrial ROS. OVLT indicates organum vasculosum of the lamina terminalis; PVN, paraventricular nucleus; PP, posterior pituitary; AP, area postrema; RVLM, rostral ventrolateral medulla. Several …

Angiotensin II Type 1a–Deficient Bone Marrow–Derived Dendritic Cells Produce Higher Levels of Monocyte Chemoattractant Protein 1

To the Editor: We read with interest the article from Crowley et al,1 who studied the role of angiotensin II type 1 (AT1) receptors (AT1aR) on immune cells in the pathogenesis of angiotensin II–induced hypertension by generating bone marrow chimeras with wild-type (WT) donors or donors lacking AT1aR. Interestingly, they found that the group of donors lacking AT1aR had more albuminuria and higher expression of a number of inflammatory mediators, including monocyte chemoattractant protein 1 (MCP-1), with persistent infiltration of macrophages in the kidney, concluding that AT1aR on bone marrow–derived cells had protective actions. The absence of a functional renin-angiotensin system, like in mice genetically lacking renin, angiotensinogen, angiotensin-converting enzyme, or AT1aR, is associated with microvascular disease and tubulointerstitial inflammation. Ouyang et al2 described that AT1a knockout (KO) mice spontaneously develop glomerular and tubulointerstitial diseases. They observed increased …

AT1 Receptor Blockade Prevents the Increase in Blood Pressure and the Augmentation of Intrarenal ANG II Levels in Hypertensive Cyp1a1-Ren2 Transgenic Rats Fed With a High-Salt Diet

IntroductionThis study was performed to determine the effects of high-salt diet on the magnitude of the increases in systolic blood pressure (SBP) and kidney tissue angiotensin (ANG) II levels that occur after induction of ANG II-dependent malignant hypertension in Cyp1a1-Ren2 transgenic rats with inducible expression of the mouse Ren2 renin gene [strain name: TGR(Cyp1a1Ren2)]. MethodsCyp1a1- Ren2 rats (n=6) were fed a normal diet containing 0.3% indole-3- carbinol (I3C) for 10days to induce ANG II-dependent malignant hypertension. ResultsRats induced with I3C exhibited increases in SBP and elevations of ANG II levels in kidney cortex and medulla. In a second group of rats (n=6), high-salt intake alone did not alter basal SBP; however, subsequent dietary administration of 0.3% I3C during continued high-salt intake elicited a substantially greater increase in SBP than observed in rats fed a normal salt diet. ANG II levels in kidney cortex and medulla of rats induced with I3C and fed a high-salt diet were elevated similarly to those in rats induced with I3C alone. Chronic administration of the AT1 receptor antagonist, losartan (100mg/L in drinking water, n=6), markedly attenuated the I3C-induced increase in SBP and prevented the augmentation of ANG II levels in kidney cortex and medulla in rats induced with I3C and maintained on a high-salt diet. ConclusionsActivation of AT1 receptors contributes to the augmented blood pressure and elevated kidney tissue ANG II levels that occur in Cyp1a1-Ren2 transgenic rats with malignant hypertension maintained on a high-salt diet.

Moderate Hyperbilirubinemia Improves Renal Hemodynamics in Angiotensin II‐Dependent Hypertension

We have previously demonstrated that moderate hyperbilirubinemia decreases blood pressure in Angiotensin (Ang) II‐dependent hypertension through mechanisms that decrease oxidative stress and increase nitric oxide levels. The goal of the present study was to examine the effect of moderate hyperbilirubinemia on glomerular filtration rate (GFR) and renal blood flow (RBF) in a mouse model of Ang II hypertension. Mice were made moderately hyperbilirubinemic by treatment with 1) indinavir or 2) morpholino antisense oligonucleotides directed against hepatic UGT1A1. Levels of unconjugated bilirubin averaged 0.57 ± 0.07, 0.92 ± 0.07, and 1.28 ± 0.1 mg/dL (n=4) in control, indinavir, and antisense treated mice, respectively. GFR and RBF were measured in mice after implantation of an osmotic minipump delivering Ang II at a rate of 1 μg/kg/min. GFR was measured by continuous infusion of I125‐iothalamate on days 7–11 of Ang II infusion in conscious mice. RBF was measured on day 10 of Ang II infusion in anesthetized mice. Treatment with either indinavir or UGT1A1 antisense significantly increased GFR in Ang II infused mice 1.2 ± 0.1, 1.9 ± 0.2, and 1.9 ± 0.1 ml/min/g kidney weight (n=4) in non‐treated, indinavir, and antisense treated mice, respectively. Next, we examined the effect of moderate hyperbilirubinemia on RBF in Ang II infused mice. Ang II infusion significantly decreased RBF and this decrease was normalized by moderate hyperbilirubinemia with RBF averaging 5.2 ± 0.5, 3.8 ± 0.2, and 4.8 ± 0.3 ml/min/g kw (n=4) in control, Ang II, and Ang II+indinavir treated mice, respectively. These results indicate that improvement of renal hemodynamics may be a mechanism by which blood pressure is lowered with moderate hyperbilirubinemia in this model. This study was supported by NIH grant HL‐088421.

The Rho exchange factor Arhgef1 mediates the effects of angiotensin II on vascular tone and blood pressure

Hypertension is one of the most frequent pathologies in the industrialized world. Although recognized to be dependent on a combination of genetic and environmental factors, its molecular basis remains elusive. Increased activity of the monomeric G protein RhoA in arteries is a common feature of hypertension. However, how RhoA is activated and whether it has a causative role in hypertension remains unclear. Here we provide evidence that Arhgef1 is the RhoA guanine exchange factor specifically responsible for angiotensin II-induced activation of RhoA signaling in arterial smooth muscle cells. We found that angiotensin II activates Arhgef1 through a previously undescribed mechanism in which Jak2 phosphorylates Tyr738 of Arhgef1. Arhgef1 inactivation in smooth muscle induced resistance to angiotensin II-dependent hypertension in mice, but did not affect normal blood pressure regulation. Our results show that control of RhoA signaling through Arhgef1 is central to the development of angiotensin II-dependent hypertension and identify Arhgef1 as a potential target for the treatment of hypertension.

A role for angiotensin II type 1 receptors on bone marrow-derived cells in the pathogenesis of angiotensin II-dependent hypertension.

Activation of type 1 angiotensin (AT(1)) receptors causes hypertension, leading to progressive kidney injury. AT(1) receptors are expressed on immune cells, and previous studies have identified a role for immune cells in angiotensin II-dependent hypertension. We, therefore, examined the role of AT(1) receptors on immune cells in the pathogenesis of hypertension by generating bone marrow chimeras with wild-type donors or donors lacking AT(1A) receptors (BMKO). The 2 groups had virtually identical blood pressures at baseline, suggesting that AT(1) receptors on immune cells do not make a unique contribution to the determination of baseline blood pressure. By contrast, in response to chronic angiotensin II infusion, the BMKOs had an augmented hypertensive response, suggesting a protective effect of AT(1) receptors on immune cells with respect to blood pressure elevation. The BMKOs had 50% more albuminuria after 4 weeks of angiotensin II-dependent hypertension. Angiotensin II-induced pathological injury to the kidney was similar in the experimental groups. However, there was exaggerated renal expression of the macrophage chemokine monocyte chemoattractant protein 1 in the BMKO group, leading to persistent accumulation of macrophages in the kidney. This enhanced mononuclear cell infiltration into the BMKO kidneys was associated with exaggerated renal expression of the vasoactive mediators interleukin-1beta and interleukin-6. Thus, in angiotensin II-induced hypertension, bone marrow-derived AT(1) receptors limited mononuclear cell accumulation in the kidney and mitigated the chronic hypertensive response, possibly through the regulation of vasoactive cytokines.

Melatonin improves cardiovascular function and ameliorates renal, cardiac and cerebral damage in rats with renovascular hypertension

The effect of melatonin was investigated in an angiotensin II-dependent renovascular hypertension model in Wistar albino rats by placing a renal artery clip (two-kidney, one-clip; 2K1C), while sham rats did not have clip placement. Starting either on the operation day or 3 wk after the operation, the rats received melatonin (10 mg/kg/day) or vehicle for the following 6 wk. At the end of the nineth week, after blood pressure (BP) and echocardiographic recordings were obtained, plasma samples were obtained to assay lactate dehydrogenase (LDH), creatine kinase (CK), antioxidant capacity (AOC), asymmetric dimethylarginine (ADMA), and nitric oxide (NOx) levels. In the kidney, heart and brain tissues, malondialdehyde (MDA) and glutathione (GSH) levels, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO) and Na(+)-K(+) ATPase activities were determined. 2K1C caused an increase in BP and left ventricular (LV) dysfunction. In hypertensive animals LDH, CK, ADMA levels were increased in plasma with a concomitant reduction in AOC and NOx. Moreover, hypertension caused a significant decrease in tissue SOD, CAT, and Na(+), K(+)-ATPase activities and glutathione content, while MDA levels and MPO activity were increased in all studied tissues. On the other hand, both melatonin regimens significantly reduced BP, alleviated oxidative injury and improved LV function. In conclusion, melatonin protected against renovascular hypertension-induced tissue damage and improved cardiac function presumably due to both its direct antioxidant and receptor-dependent actions, suggesting that melatonin may be of therapeutic use in preventing oxidative stress due to hypertension.

Reduction of oxidative stress does not attenuate the development of angiotensin II-dependent hypertension in Ren-2 transgenic rats

Results of our previous studies have suggested that enhanced generation of superoxide (O 2 −) may contribute to the pathophysiology of hypertension in Ren-2 transgenic rats (TGR). The present study was performed to evaluate in TGR the effects of chronic treatment with the O 2 − scavenger tempol and the antioxidant apocynin on the development of hypertension. Systolic blood pressure (SBP) was monitored from 30 to 99 days of age in TGR and in normotensive Hannover Sprague–Dawley (HanSD) rats. At the end of the experiment, urinary protein and 8-isoprostane excretion were determined and angiotensin II (ANG II) and malondialdehyde (MDA) levels were measured in kidney and cardiac tissues. Cardiac hypertrophy was assessed as the ratio of left heart ventricle weight to tibia length (LVW/TL). Although tempol and apocynin treatment in TGR significantly decreased 8-isoprostane excretion and MAD tissue concentrations as compared with untreated TGR, it did not alter the course of SBP, LVW/TL ratio, proteinuria or ANG II levels that were enhanced as compared with HanSD rats. Our data suggest that the development of hypertension in TGR is clearly ANG II-dependent but the contribution of oxidative stress to the development of hypertension in this model appears to be negligible.

Response to Method of Blood Collection May Explain the Suppression of Plasma Renin Concentration in Prorenin Transgenic Mice

HomeHypertensionVol. 54, No. 1Response to Method of Blood Collection May Explain the Suppression of Plasma Renin Concentration in Prorenin Transgenic Mice Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessLetterPDF/EPUBResponse to Method of Blood Collection May Explain the Suppression of Plasma Renin Concentration in Prorenin Transgenic Mice Timothy L. Reudelhuber Timothy L. ReudelhuberTimothy L. Reudelhuber Laboratory of Molecular Biochemistry of Hypertension, Clinical Research Institute of Montreal, and, Department of Medicine, University of Montreal, Montreal, Quebec, Canada Search for more papers by this author Originally published26 May 2009https://doi.org/10.1161/HYPERTENSIONAHA.109.134908Hypertension. 2009;54:e13Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: May 26, 2009: Previous Version 1 In responding to the letter by Campbell,1 it is important to point out that this issue has no bearing on the major finding of our article,2 that elevations in plasma prorenin alone do not result in cardiac or renal pathologies. Nevertheless, Campbell1 brings up an important issue, that measurement of plasma renin concentration (PRC) is fraught with potential artifacts. In addition to the ability of stress and anesthesia to cause an acute release of renin, the mouse is particularly sensitive to blood pressure decreases resulting from sampling too much blood because of its small blood volume compared with rats and humans. We are aware of all of these factors and have developed sampling and assay techniques that are reproducible and reflect the expected physiological modulation of PRC. We apologize for not including these details in our most recent article, and they are described below.Mice are lightly anesthetized with ether, and blood is collected from the retro-orbital sinus with a short heparinized microhematocrit capillary tube. No more than 3 drops of blood are collected into a microcentrifuge tube containing 10 μL of 100-mmol/L EDTA (pH 7.4). Every effort is made to perform the blood collection swiftly and without stress to the animal. Plasma is recovered and immediately frozen at −80°C until the assay is performed. On the day of the assay we thaw the sample on the bench and perform the angiotensin I generation assay in the presence of EDTA, PMSF (inactivates trypsin and other serine proteases), and 8-hydroxyquinoline (inhibits breakdown of angiotensin peptides).Although it is very difficult to prove that we have no artifact in our renin measurements, we have found that this method gives lower renin concentrations in control mice than other sampling methods that we have tried (saphenous vein, cheek pouch, etc). In addition, our TTR-mProren-7 mice develop an angiotensin II-dependent hypertension (Figure 5 of the article2), and their PRCs drop, as would be expected, because both pressure and angiotensin II are known to suppress renin release from the kidney. Moreover, when we place mice on pharmacological inhibitors of the renin-angiotensin system (eg, angiotensin-converting enzyme inhibitors) for as little as 5 days, their PRCs increase up to 15-fold (our unpublished results), as would be expected when removing angiotensin II feedback suppression. Thus, our assay reflects the expected physiological modulation of PRC.In conclusion, we agree with Campbell1 that animal handling, anesthesia, and assay methods can affect PRC measurements, but we remain convinced that the conditions that we use reflect the normal and expected regulation of kidney renin by blood pressure and angiotensin II, and the results do not justify the suspicion of an assay artifact.DisclosuresNone.1 Campbell DJ. Method of blood collection may explain the suppression of plasma renin concentration in prorenin transgenic mice. Hypertension. 2009; 54: e12.LinkGoogle Scholar2 Mercure C, Prescott G, Lacombe MJ, Silversides DW, Reudelhuber TL. Chronic increases in circulating prorenin are not associated with renal or cardiac pathologies. Hypertension. 2009; 53: 1062–1069.LinkGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetails July 2009Vol 54, Issue 1 Advertisement Article InformationMetrics https://doi.org/10.1161/HYPERTENSIONAHA.109.134908 Originally publishedMay 26, 2009 PDF download Advertisement SubjectsAnimal Models of Human DiseaseHypertensionHypertrophy

In hypertension, the kidney breaks your heart

The renin-angiotensin system (RAS) is a master regulator of blood pressure and fluid homeostasis. Because RAS components are expressed in several tissues that may influence blood pressure, studies using conventional gene targeting to globally interrupt the RAS have not determined the contributions of angiotensin II receptor type 1 (AT(1)) receptors in specific tissue pools to blood pressure regulation and tissue injury. Recent experiments using kidney cross-transplantation and mice lacking the dominant murine AT(1) receptor isoform, AT(1A), have demonstrated that 1) AT(1) receptors inside and outside the kidney make equivalent contributions to normal blood pressure homeostasis, 2) activation of renal AT(1) receptors is required for the development of angiotensin II-dependent hypertension, and 3) this blood pressure elevation rather than activation of AT(1) receptors in the heart drives angiotensin II-induced cardiac hypertrophy. These findings, together with previous experiments, confirm the kidney's critical role in the pathogenesis of hypertension and its complications.

Colfibrate attenuates blood pressure and sodium retention in DOCA-salt hypertension

Clofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR alpha) agonist, increases renal tubular cytochrome P450 4a (Cyp4a) expression thereby increasing 20-hydroxyeicosatetraenoic acid (20-HETE) production. To determine if clofibrate affects blood pressure regulation we studied mice with DOCA-salt induced hypertension in wild-type and PPAR alpha knockout mice. Wild-type mice treated with DOCA-salt had higher mean arterial pressures and higher cumulative sodium balance, but lower renal 20-HETE production than did vehicle-treated mice. Treating DOCA-salt mice with clofibrate attenuated the increase in mean arterial pressure and cumulative sodium balance while increasing 20-HETE production and renal Cyp4a expression. In contrast the PPAR alpha knockout mice treated with clofibrate and DOCA-salt showed no attenuation in the increase of blood pressure, cumulative sodium balance, renal 20-HETE production or Cyp4a protein expression. Expression of the PPAR alpha protein was greater in proximal tubules than in renal microvessels. Our results show that PPAR alpha pathway induces renal tubular 20-HETE production which affects sodium retention and blood pressure regulation in DOCA-salt-treated mice.

Pivotal role of angiotensin II receptor subtype 1A in the development of two-kidney, one-clip hypertension: study in angiotensin II receptor subtype 1A knockout mice

The present study was performed to examine in two-kidney, one-clip (2K1C) Goldblatt hypertensive mice: first, the relative contribution of angiotensin II receptor subtypes 1A (AT(1A)) and 1B (AT(1B)); second, the role of angiotensin II type 2 (AT(2)) receptors in the development of hypertension in wild-type (AT(1A)+/+) and AT(1A) receptor knockout (AT(1A)-/-) mice; and third, the role of increased nitric oxide synthase activity in counteracting the hypertensinogenic action of angiotensin II in this model. AT(1A)+/+ and AT(1A)-/- mice underwent clipping of one renal artery and were infused with either saline vehicle or selective AT(2) receptor agonist CGP-42112A (CGP). Blood pressure was monitored by radiotelemetry. Blood pressure responses to the nitric oxide synthase inhibitor nitro-L-arginine-methyl-ester were evaluated. AT(1A)+/+ mice responded to clipping by a rise in blood pressure that was not modified by CGP infusion. Clip placement caused a slight increase in blood pressure in AT(1A)-/- mice that remained significantly lower than in AT(1A)+/+ mice. Acute nitric oxide synthase inhibition caused greater increase in blood pressure in 2K1C/AT(1A)+/+ than in AT(1A)+/+ mice. The present data support the critical role of AT(1A) receptors in the development of 2K1C hypertension, whereas AT(1B) receptors play only a minor role in blood pressure regulation in this model of angiotensin II-dependent hypertension. Activation of AT(2) receptors does not play an antagonistic role in the AT(1) receptor-mediated hypertensinogenic actions of angiotensin II in this model. Finally, enhanced nitric oxide synthase activity plays a protective role by counteracting the vasoconstrictor influences of angiotensin II in 2K1C hypertensive mice.