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Information on the regional concentrations of angiotensin (Ang) II and its type-1 and -2 receptors (AT(1)R, AT(2)R) in the kidney is still incomplete. Published data on the levels of arterially delivered Ang I and II (Ang Ia, Ang IIa) and intrarenally produced Ang I and II (Ang Ii, Ang IIi) in the renal vein and in whole tissue were analyzed by using a kinetic model of Ang production and distribution in the glomerular and peritubular cortical tissue regions (Glom, Pt). (1) 90% of Ang II is cell-associated, due to its binding to AT(1)R and AT(2)R; (2) most Ang II in the renal cortex is Ang IIi; (3) Ang IIa is mainly localized in Glom; (4) Ang Ii rather than Ang Ia is a substrate of renal angiotensin-converting enzyme; (5) Ang IIi is localized in Pt and its concentration in interstitial fluid is 5-15 times the Ang II concentration in arterial plasma; and (6) in Glom the interstitial concentration of cell surface-bound AT(1)R is above 200K(d), and in Pt the AT(1)R and AT(2)R concentrations are above 10K(d). In conclusion, endocrine Ang II mainly acts in Glom, whereas Pt is exposed to paracrine Ang II generated by the conversion of intrarenally produced Ang I. High AT(1)R concentrations in Glom and Pt favor diffusion-limited binding, so that the apparent binding rate constant at sites closest to the source of Ang II delivery is greatly increased. Results may explain why the kidney is responsive to low levels of endocrine Ang II, despite its high content of paracrine Ang II.

Information on the levels of angiotensin II (Ang II) and its receptors in the various renal tissue compartments is still incomplete. A model is presented describing the kinetics of Ang II production, distribution, and disposal in the renal cortex. Basic features are: (1) the model is designed to derive, from Ang II measurements in blood and in whole tissue, estimates of the local densities of the Ang II type 1 (AT(1)) and type 2 (AT(2)) receptors, and to calculate the concentrations of endocrine and paracrine Ang II they actually 'see'; (2) glomerular and peritubular tissue are conceived as separate regions (glomerular region (Glom), peritubular region (Pt)); (3) in Glom and in Pt, Ang II is homogeneously distributed in capillary blood and in interstitial fluid; (4) the model allows for local Ang II concentration gradients between interstitium and blood; (5) Ang II from the circulation diffuses into the interstitium of Glom after convective transcapillary transport; (6) Ang II produced in tubules or Pt enters the microcirculation through diffusive overflow from interstitium; (7) the presence of cell-surface-bound Ang II depends on the reaction with AT(1) and AT(2) receptors, and the presence of intracellular Ang II depends on the internalization of Ang II - AT(1) receptor complex; and (8) the model provides for glomerular filtration, vasopeptidase-mediated degradation, and intracellular degradation as mechanisms of elimination. This model can serve as a framework for detailed quantitative studies of the renin-angiotensin system in the kidney.

Background: Increasing evidence suggests that angiotensin-(1-7) [Ang-(1-7)] acts as an endogenous antagonist of Ang II when the renin-angiotensin system (RAS) is activated. In the present study, we therefore compared the effects of acute intrarenal (i.r.) Ang-(1-7) receptor blockade on renal function under conditions of normal and increased intrarenal Ang II concentration., Methods: Salt-replete Hannover-Sprague Dawley rats (HanSD) served as control animals. As models with enhanced action of Ang II we first used transgenic rats harboring the Ren-2 renin gene (TGR), second, Ang II-infused rats, third, 2-kidney, 1-clip (2K1C) hypertensive rats on normal salt intake, and fourth, salt-depleted TGR and HanSD., Results: I.r. Ang-(1-7) receptor blockade elicited significant decreases in glomerular filtration rate (GFR), renal plasma flow (RPF), and sodium excretion in 2K1C rats, and in salt-depleted TGR and HanSD. In contrast, i.r. Ang-(1-7) receptor blockade did not significantly change GFR, RPF, and sodium excretion in salt-replete TGR and HanSD, or in Ang II-infused rats., Conclusion: These findings suggest that under conditions of normal intrarenal RAS activity and increased intrarenal Ang II action by infusion of Ang II or by insertion of a renin gene in salt-replete conditions, Ang-(1-7) is not an important factor in the regulation of renal function. In contrast, under conditions of endogenous RAS activation due to clipping of the renal artery or to sodium restriction, Ang-(1-7) serves as opponent of the vasoconstrictor actions of Ang II.

In experiments designed to analyze cardiovascular structure in response to antihypertensive therapy with an ACE inhibitor, we decided to start very early in life with the aim to prevent blood pressure increases and the development of vascular structural changes. In these treated groups of rats we unexpectedly observed that after they were weaned, their water consumption and urine volume, respectively, increased substantially. The present study was designed to determine if inhibition of the renin-angiotensin system produced similar effects in different strains of rats, and focused on characterizing the abnormal fluid balance occurring as a consequence to neonatal treatment with ACE inhibitors or angiotensin II blockers. Three-day-old Wistar Kyoto (WKY), Wistar (WR) and spontaneously hypertensive rats (SHR) were given either saline, enalapril, captopril, losartan and the AT2 blocker, PD123319, in the same amount of volume for 20 days. Treatment was stopped and rats were examined with regard to renal morphology at 4, 14 and 30 weeks of age. In addition, water consumption, urine volume, urine electrolytes and osmolality were analyzed at 14 weeks of age, that is, 10 weeks off treatment. Early treatment with the ACE inhibitors, enalapril and captopril, and the AT1 blocker, losartan, but not the AT2 blocker, PD 123319, in the SHR and in the normotensive strains WKY and WR produced persistent, irreversible histopathological renal abnormalities in adult life, long after the rats had been taken off treatment. These abnormalities consisted of mainly cortical tubulointerstitial inflammation, various degrees of papillary atrophy and pelvic dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

The non-osmotic release of arginine vasopressin (AVP) is associated with the concomitant activation of the renin-angiotensin and sympathetic nervous systems. In vivo studies suggest that a positive interaction may occur between AVP and angiotensin II (Ang II), and other Ca2+ mobilizing hormones. In the present study, the cellular mechanisms of this interaction between AVP and Ang II in vascular smooth muscle cell (VSMC) were examined. These results support the existence of a positive interaction between AVP and Ang II on Ca2+ mobilization in VSMC. In fact, the challenge of VSMC with combined AVP and Ang II, in a range from 5 x 10(-11) to 10(-8) M, enhanced cytosolic free Ca2+ ([Ca2+]i) and 45Ca2+ efflux in a more than additive manner. This potentiation, which was not dependent of the presence of extracellular calcium, correlated with an increased VSMC shape change. Moreover, the combination of subthreshold doses of AVP and Ang II (5 x 10(-11) M), which do not release Ca2+ alone, evoked a Ca2+ mobilizing response. A subthreshold dose of Ang II also shifted to the left the concentration-response curve of the AVP-mediated 45Ca2+ efflux. Since there were no changes in receptor binding of either hormone by the other hormone and the interaction of the two hormones on the production of inositol phosphatides was additive, the AVP and AII positive interaction on Ca2+ mobilization on VSMC may occur at the level of the intracellular Ca2(+)-releasing mechanism itself. Such an interaction can occur at hormone concentrations below the Ca2+ release threshold and may explain an increased functional response to the combination of pressor hormones compared to that of each hormone alone.

To evaluate the effects of angiotensin converting enzyme inhibition (SQ 20881, CEI) on superficial nephron function of the non-clipped kidney in Goldblatt hypertensive rats in the absence of alterations in renal arterial pressure, control renal arterial pressure (RAP) was reduced first to the range generally obtained during CEI (124 +/- 4 mm Hg). RAP was maintained during the CEI period by adjustment of a suprarenal aortic clamp. At the reduced RAP, whole kidney and single nephron glomerular filtration rates (GFR) were reduced from the hypertensive levels and were lower than the measurements in normotensive control rats. During CEI, whole kidney GFR and single nephron GFR increased by 55 and 42%, respectively. There were decreases in absolute as well as fractional proximal reabsorption rates. In the intermediate nephron segment, fractional reabsorption was decreased, but absolute fluid reabsorption increased in proportion to the increased delivery rate. Proximal tubule and peritubular capillary hydrostatic pressures increased significantly during CEI also. These results indicate that an increased activity of the renin-angiotensin system occurring in Goldblatt hypertensive rats subjected to aortic constriction exerts effects to lower GFR and increase proximal reabsorption rate. The concomitant superficial nephron and whole kidney GFR responses to CEI when arterial pressure was maintained suggests that the pre-existing levels of angiotensin exerted similar influences on the total nephron population.

The current investigation was performed to determine whether there are changes in the renin-angiotensin system with increasing age in rats. Experiments were performed on male Sprague-Dawley rats (50 to 165 days old). There were no changes in plasma renin activity or angiotensin II concentrations, but the number of angiotensin II binding sites in isolated glomeruli increased with increasing age (r = 0.87, P less than 0.01). Since rat weight varies directly with age, we studied the possibility that the increase in receptor number was due to changes in glomerular morphometrics. In a separate group of experiments the diameter of isolated glomeruli was measured, and assuming spherical shape, glomerular volume and surface area were calculated. Glomerular diameter increased with age and weight of the rats (r = 0.99, P less than 0.001). There was a strong linear correlation between the changes in angiotensin II receptor number and glomerular surface area (r = 0.99, P less than 0.001). The number of receptors per unit surface area was independent of rat weight or age (1224 receptors/micron 2). To test the hypothesis that the apparent increase in glomerular angiotensin II receptor sites with increasing age was due to the shape of the glomerulus, additional binding studies were performed on membranes prepared from isolated glomeruli. There were no differences in the number of angiotensin II receptors in membranes from 63 and 112 day-old rats (888 +/- 115 vs. 925 +/- 128 fmol/mg). In additional experiments the effects of increasing age on angiotensin modulation of renal function were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of rats to elevated dietary salt following recovery from acute kidney injury (AKI) accelerates the transition to chronic kidney disease (CKD), and is dependent on lymphocyte activity. Here we tested whether high salt diet triggers lymphocyte activation in postischemic kidneys to worsen renal inflammation and fibrosis. Male Sprague-Dawley rats on a 0.4% salt diet were subjected to left unilateral ischemia-reperfusion and allowed to recover for 5 weeks. This resulted in a mild elevation of CD4(+) T cells relative to sham animals. Contralateral unilateral nephrectomy and elevated dietary salt (4%) for 4 extra weeks hastened CKD and interstitial fibrosis. Activated T cells were increased in the kidney threefold after 4 weeks of elevated dietary salt exposure relative to post-AKI rats before salt feeding. The T cell subset was largely positive for IL-17, indicative of Th-17 cells. Because angiotensin II activity may influence lymphocyte activation, injured rats were given the AT1R antagonist, losartan, along with high salt diet. This significantly reduced the number of renal Th-17 cells to levels of sham rats, and significantly reduced the salt-induced increase in fibrosis to about half. In vitro studies in AKI-primed CD4(+) T cells indicated that angiotensin II and extracellular sodium enhanced, and losartan inhibited, IL-17 expression. Thus, dietary salt modulates immune cell activity in postischemic recovering kidneys because of the activity of local RAS, suggesting the participation of these cells in CKD progression post-AKI. [ABSTRACT FROM AUTHOR]

Proteinuria is a central component of chronic kidney disease and an independent risk factor for cardiovascular disease. Kidney podocytes have an essential role as a filtration barrier against proteinuria. Kruppel-like Factor 4 (KLF4) is expressed in podocytes and decreased in glomerular diseases leading to methylation of the nephrin promoter, decreased nephrin expression and proteinuria. Treatment with an angiotensin receptor blocker (ARB) reduced methylation of the nephrin promoter in murine glomeruli of an adriamycin nephropathy model with recovery of KLF4 expression and a decrease in albuminuria. In podocyte-specific KLF4 knockout mice, the effect of ARB on albuminuria and the nephrin promoter methylation was attenuated. In cultured human podocytes, angiotensin II reduced KLF4 expression and caused methylation of the nephrin promoter with decreased nephrin expression. In patients, nephrin promoter methylation was increased in proteinuric kidney diseases with decreased KLF4 and nephrin expression. KLF4 expression in ARB-treated patients was higher in patients with than without ARB treatment. Thus, angiotensin II can modulate epigenetic regulation in podocytes and ARB inhibits these actions in part via KLF4 in proteinuric kidney diseases. This study provides a new concept that renin-angiotensin system blockade can exert therapeutic effects through epigenetic modulation of the kidney gene expression. [ABSTRACT FROM AUTHOR]

Agents blocking the renin-angiotensin-aldosterone system are frequently used in patients with end-stage renal disease, but whether they exert beneficial cardiovascular effects is unclear. Here the long-term effects of the angiotensin II receptor blocker, irbesartan, were studied in hemodialysis patients in a double-blind randomized placebo-controlled 1-year intervention trial using a predefined systolic blood pressure target of 140 mm Hg (SAFIR study). Each group of 41 patients did not differ in terms of age, blood pressure, comorbidity, antihypertensive treatment, dialysis parameters, and residual renal function. Brachial blood pressure decreased significantly in both groups, but there was no significant difference between placebo and irbesartan. Use of additional antihypertensive medication, ultrafiltration volume, and dialysis dosage were not different. Intermediate cardiovascular end points such as central aortic blood pressure, carotid-femoral pulse wave velocity, left ventricular mass index, N-terminal brain natriuretic prohormone, heart rate variability, and plasma catecholamines were not significantly affected by irbesartan treatment. Changes in systolic blood pressure during the study period significantly correlated with changes in both left ventricular mass and arterial stiffness. Thus, significant effects of irbesartan on intermediate cardiovascular end points beyond blood pressure reduction were absent in hemodialysis patients. [ABSTRACT FROM AUTHOR]

Angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP) promotes AT1R internalization along with suppression of pathological activation of tissue AT1R signaling. However, the functional significance of ATRAP in renal sodium handling and blood pressure regulation under pathological stimuli is not fully resolved. Here we show the blood pressure of mice with a gene-targeted disruption of ATRAP was comparable to that of wild-type mice at baseline. However, in ATRAP-knockout mice, angiotensin II-induced hypertension was exacerbated and the extent of positive sodium balance was increased by angiotensin II. Renal expression of the sodium-proton antiporter 3, a major sodium transporter in the proximal tubules, urinary pH, renal angiotensinogen production, and angiotensin II content was unaffected. Stimulation of the renal expression and activity of the epithelial sodium channel (ENaC), a major sodium transporter in the distal tubules, was significantly enhanced by chronic angiotensin II infusion. The circulating and urinary aldosterone levels were comparable. The blood pressure response and renal ENaC expression by aldosterone were not affected. Thus, ATRAP deficiency exacerbated angiotensin II-mediated hypertension by pathological activation of renal tubular AT1R by angiotensin II. This directly stimulates ENaC in the distal tubules and enhances sodium retention in an aldosterone-independent manner. [ABSTRACT FROM AUTHOR]

Chan et al. report increased mortality with angiotensin-converting enzyme inhibitors and angiotensin type 1 receptor blockers in hemodialysis patients, supporting emerging evidence that such dual therapy may be detrimental. We speculate that effects of reactive renin and prorenin release on the (pro)renin receptor may explain this apparent paradox, either through membrane-bound generation of angiotensin II or via stimulation of signal transduction pathways. Potential benefits of direct renin inhibitors and yet-to-be-developed (pro)renin receptor blockers are discussed. [ABSTRACT FROM AUTHOR]

Intrarenally synthesized angiotensin II (Ang II) may be involved in the progression of glomerulonephritis, leading to irreversible glomerulosclerosis. There is increasing evidence that systemic angiotensin receptor blocker (ARB) treatment has beneficial effect on the prognosis of progressive glomerulonephritis and diabetic nephropathy. However, the cellular and molecular mechanisms behind this therapeutic effect of ARB remain unclear. In this study, we used a novel strategy of local ARB delivery via type-1 collagen sponge, to treat progressive glomerulonephritis that would result in irreversible glomerulosclerosis in our previously established rat model. At days 9 and 14 after disease induction, mild proteinuria, 20.7±4.7 and 10±1.3 mg/day, was found. Local ARB treatment reduced proteinuria significantly to 3.19±3.2 and 5.25±0.95 mg/day (P<0.01), respectively. Scoring of glomerular matrix expansion and sclerotic index revealed that local ARB treatment significantly ameliorated glomerular pathology. Ang II type 1 receptor mRNA expression was remarkably enhanced in the Ang II group and ARB treatment reversed this effect at 14 days. Local delivery of ARB significantly improved glomerular blood flow levels, compared to the untreated disease control group, from 710±18.25 to 859.44±22.86 μm/s, respectively. Local delivery of ARB into the kidney affected local RAS and thus improved the renal injury and function in the potentially progressive glomerulosclerosis of rat model.Kidney International (2006) 70, 1591–1598. doi:10.1038/sj.ki.5001872; published online 20 September 2006 [ABSTRACT FROM AUTHOR]

Type 2 diabetes is becoming the leading cause of end-stage renal disease (ESRD) worldwide. Prevalence of ESRD and the antihypertensive response to renin–angiotensin system intervention are suggested to vary among different ethnicities. The Reduction in Endpoints in Non-insulin dependent diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) study, which included different ethnic groups, demonstrated a renoprotective effect of losartan. A post hoc analysis from RENAAL was performed where we examined in each ethnic group the ESRD risk, identified independent predictors for ESRD, effect of degree of baseline albuminuria, effect of 6-month antiproteinuric response to therapy on ESRD, and renoprotective effect of losartan assessed by albuminuria reduction and ESRD. Baseline albuminuria was the strongest predictor for ESRD in every ethnic group. Albuminuria reduction was associated with reduced risk of ESRD while losartan reduced albuminuria in every ethnic group. When accounting for independent predictors of ESRD, losartan exhibited renoprotection in all ethnic groups. In this type 2 diabetic population with nephropathy, baseline albuminuria is the predominant risk parameter for ESRD; early antiproteinuric effect of losartan predicts long-term renoprotection; and losartan appears to be renoprotective in all ethnic groups. Since the RENAAL study was not powered to determine ethnic responses, these results underline the need for prospective trials where the aim is renal protection among different ethnic groups.Kidney International (2006) 69, 1675–1682. doi:10.1038/sj.ki.5000326; published online 29 March 2006 [ABSTRACT FROM AUTHOR]

Progression of diabetic nephropathy appears directly related to renal tubulointerstitial injury, but the involved genes are incompletely delineated. To identify such genes, DNA microarray analysis was performed with RNA from renal proximal tubules (RPTs) of streptozotocin-induced diabetic Wistar rats, spontaneously diabetic BioBreeding rats, and rat immortalized renal proximal tubular cells (IRPTCs) exposed to high glucose (25 mM) medium for 2 weeks. Osteopontin (OPN) mRNA expression was quantified by real time-quantitative polymerase chain reaction (RT-qPCR) or conventional reverse transcriptase-polymerase chain reaction (RT-PCR). OPN mRNA expression was upregulated (5–70-fold increase) in diabetic rat RPTs and in IRPTCs chronically exposed to high glucose compared to control RPTs and IRPTCs. High glucose, angiotensin II, phorbol 12-myristate 13-acetate and transforming growth factor-beta 1 (TGF-β1) stimulated OPN mRNA expression in IRPTCs in a dose- and time-dependent manner. This effect was inhibited by tiron, taurine, diphenylene iodinium, losartan, perindopril, calphostin C, or LY 379196 but not PD123319. IRPTCs overexpressing dominant-negative protein kinase C-beta 1 (PKC-β1) cDNA or antisense TGF-β1 cDNA prevented the high glucose effect on OPN mRNA expression. We concluded that high glucose-mediated increases in OPN gene expression in diabetic rat RPTs and IRPTCs are mediated, at least in part, via reactive oxygen species generation, intrarenal rennin–angiotensin system activation, TGF-β1 expression, and PKC-β1 signaling.Kidney International (2006) 69, 1005–1015. doi:10.1038/sj.ki.5000206; published online 1 February 2006 [ABSTRACT FROM AUTHOR]

Background: Angiotensin-converting enzyme (ACE)2, a homologue of ACE, which is insensitive to ACE inhibitors and forms angiotensin-(1-7) [Ang-(1-7)] from angiotensin II (Ang II) with high efficiency was investigated in response to chronic blockade with lisinopril, losartan, and both drugs combined.Methods: Thirty-six adult Lewis rats were assigned to receive these medications in their drinking water for 2 weeks while their arterial pressure, water intake, and urine volume were recorded throughout the study. Measures of renal excretory variables included assessing excretion rates of angiotensin I (Ang I), Ang II and Ang-(1-7) while blood collected at the completion of the study was used for measures of plasma angiotensin concentrations. Samples from renal cortex were assayed for renin, angiotensinogen (Aogen), neprilysin, angiotensin types 1 and 2 (AT(1) and AT(2)) and mas receptor mRNAs by semiquantitative reverse transcriptase (RT) real-time polymerase chain reaction (PCR). ACE2 activity was determined as the rate of Ang II conversion into Ang-(1-7).Results: Comparable blood pressure reductions were obtained in rats medicated with either lisinopril or losartan, whereas both drugs produced a greater decrease in arterial pressure. Polyuria was recorded in all three forms of treatment associated with reduced osmolality but no changes in creatinine excretion. Lisinopril augmented plasma levels and urinary excretion rates of Ang I and Ang-(1-7), while plasma Ang II was reduced with no effect on urinary Ang II. Losartan produced similar changes in plasma and urinary Ang-(1-7) but increased plasma Ang II without changing urinary Ang II excretion. Combination therapy mimicked the effects obtained with lisinopril on plasma and urinary Ang I and Ang-(1-7) levels. Renal cortex Aogen mRNA increased in rats medicated with either lisinopril or the combination, whereas all three treatments produced a robust increase in renal renin mRNA. In contrast, ACE, ACE2, neprilysin, AT(1), and mas receptor mRNAs remained unchanged with all three treatments. Renal cortex ACE2 activity was significantly augmented in rats medicated with lisinopril or losartan but not changed in those given the combination.Conclusion: Our data revealed a role for ACE2 in Ang-(1-7) formation from Ang II in the kidney of normotensive rats as primarily reflected by the increased ACE2 activity measured in renal membranes from the kidney of rats given either lisinopril or losartan. The data further indicate that increased levels of Ang-(1-7) in the urine of animals after ACE inhibition or AT(1) receptor blockade reflect an intrarenal formation of the heptapeptide. [ABSTRACT FROM AUTHOR]

AGEs activate mesangial TGF-β–Smad signaling via an angiotensin II type I receptor interaction.Background.The renin-angiotensin system (RAS) and the accumulation of advanced glycation end products (AGEs) have been implicated in the pathogenesis of diabetic nephropathy. Whether there is a functional interaction between the RAS and AGEs in diabetic nephropathy is not known. In this study, we investigated whether AGEs could activate autocrine angiotensin II (Ang II) signaling and subsequently induce transforming growth factor-β (TGF-β)–Smad signaling in cultured rat mesangial cells.Methods.The intracellular formation of reactive oxygen species (ROS) was detected using the fluorescent probe CM-H2DCFDA. Ang II was measured by radioimmunoassay. TGF-β released into media was quantitatively analyzed in an enzyme-linked immunosorbent assay (ELISA). Smad2, p27Kip1 (p27), fibronectin, and receptor for AGEs (RAGE) protein expression were determined by Western blot analysis. TGF-β–inducible promoter activity was analyzed by a luciferase assay. DNA synthesis was evaluated by 5-bomo-2′-deoxyuridine (BrdU) incorporation and de novo protein synthesis was determined by[3H]leucine incorporation.Results.AGEs increased intracellular ROS generation in mesangial cells, and this effect was significantly inhibited by an antiserum against RAGE. AGEs also were found to stimulate Ang II production in a time- and dose-dependent manner, which was completely prevented by an antioxidant,N-acetylcysteine (NAC). AGE-induced TGF-β overproduction was completely blocked by candesartan, an Ang II type 1 receptor (AT1R) antagonist. Both candesartan and neutralizing antibody against TGF-β completely prevented AGEs-induced Smad2 phosphorylation and TGF-β–inducible promoter activity. Furthermore, AGEs were found to inhibit DNA synthesis and to stimulate de novo protein synthesis and fibronectin production in association with up-regulation of p27. All of these phenomena were completely prevented by candesartan or a polyclonal antibody against TGF-β.Conclusion.The present study suggests that AGE-RAGE–mediated ROS generation activates TGF-β–Smad signaling and subsequently induces mesangial cell hypertrophy and fibronectin synthesis by autocrine production of Ang II. This pathway may provide an important link between metabolic and haemodynamic factors in promoting the development and progression of diabetic nephropathy. [ABSTRACT FROM AUTHOR]

Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis. Background. The renin-angiotensin system (RAS) seems to play a pivotal role in progression of immunoglobulin A (IgA) nephropathy (IgAN). Accordingly, in patients with IgAN a relationship between the RAS and the fibrogenic cascade triggered by transforming growth factor-β1 (TGF-β1) should be observed. This study was carried out to obtain deeper insight into the regulation of RAS and the interaction with TGF-β1 in the diseased kidney. Methods. Twenty renal biopsies from IgAN patients and five from renal cancer patients (controls) were analyzed in both microdissected glomerular and tubulointerstitial compartments by reverse transcription-polymerase chain reaction (RT-PCR). All patients had normal renal function. The expression of the following genes was determined: angiotensinogen (Agtg ), renin, angiotensin-converting enzyme (ACE ), angiotensin II (Ang II) type 1 and type II (AT1 and AT2 receptors ), TGF-β1 , collagen IV (Coll IV ), α-smooth muscle actin (α-SMA ). Quantitative data were confirmed for TGF-β1 and ACE genes by real-time PCR. Results. RAS genes were overexpressed in IgAN patients vs. control subjects. There was no difference between glomerular and tubulointerstitial RAS gene expression levels. On the contrary, the overactivation of fibrogenic cascade genes (TGF-β1 , Coll IV , α-SMA ) in the tubulointerstitium was observed (TGF-β1 , glomerular 0.14 ± 0.10 SD; tubulointerstial 0.34 ± 0.20; P = 0.000) (α-SMA , glomerular 0.08 ± 0.07; tubulointerstitial 0.35 ± 0.19; P = 0.000) (Coll IV , glomerular 0.12 ± 0.11; tubulointerstitial 0.22 ± 0.10; P = 0.03). This fibrogenic cascade seems to be triggered by RAS as indicated by statistically significant correlations between the expression of their respective genes. A direct relationship between the putative Ang II... [ABSTRACT FROM AUTHOR]

Angiotensin II infusion ameliorates the early phase of a mesangioproliferative glomerulonephritis. Background. Inhibition of the renin-angiotensin system slows the progression of chronic renal disease. Methods. To test whether angiotensin II (Ang II) infusion aggravates or ameliorates an acute glomerulonephritis, the peptide was infused (200 ng/min by osmotic minipump) in rats with an anti-thymocyte antibody-induced glomerulonephritis (ATS). Results. Ang II significantly increased blood pressure. Following injection of the antibody, similar glomerular binding of rabbit IgG and rat complement C3 was detected in ATS and Ang II+ATS rats, indicating no differences in delivery and binding of the antibody. Ang II infusion, however, induced a significant reduction in glomerular monocyte infiltration, cell proliferation and matrix expansion in nephritic rats compared to rats with nephritis without Ang II. The antiproliferative effect of Ang II was inhibited by the Ang II type 1 (AT1) receptor blocker irbesartan, but not by the AT2 receptor blocker PD 123319, indicating that this effect was likely transduced by AT1 receptors. Norepinephrine infusion (600 ng/min) produced a similar degree of hypertension, but did not affect glomerular proliferation in nephritic rats. Ang II induced the glomerular expression of the cell cycle inhibitor p27KIP1 and of transforming growth factor-β (TGF-β) and inhibited expression of monocyte chemotactic protein 1 (MCP-1). Conclusion. Ang II surprisingly ameliorates glomerular monocyte infiltration, proliferation and matrix expansion in ATS nephritis. Ang II-mediated induction of cyclin kinase inhibitors and TGF-β may contribute to the protection of the glomerulus from inflammatory injury by inducing cell cycle arrest and attenuating activation of local and recruited cells. Alternatively, Ang II might protect the kidney at least in part by less inflow of disease activators due to reduction of renal blood flow.... [ABSTRACT FROM AUTHOR]

Background: In rats maintained on a high salt diet (H/S) to suppress basal renal angiotensinogen levels, angiotensin II (Ang II) infusion for 13 days increased renal angiotensinogen mRNA and protein, thus providing a mechanism for further augmentation of intrarenal Ang II levels. The present study tested the hypothesis that enhanced intrarenal angiotensinogen formation during Ang II infusion is reflected by secretion into the tubular fluid leading to increased urinary excretion of angiotensinogen (UAGT).Methods: The effects of chronic Ang II infusion were examined on kidney and plasma Ang II levels and UAGT in male Sprague-Dawley rats maintained on an 8% salt diet for three weeks (N=10). Following one week on the H/S diet, Ang II (40 ng/min) was administered for two weeks via an osmotic minipump to one group (H/S + Ang II, N=5), while the remaining rats were sham-operated (H/S + Sham, N=5). Additionally, a control group was prepared with normal salt diet and sham-operation (N/S + Sham, N=5).Results: H/S alone did not alter systolic blood pressure (BP) (103 +/- 2 vs. 104 +/- 2 mm Hg), while Ang II infusion to H/S rats significantly increased systolic BP from 103 +/- 2 to 154 +/- 2 after two weeks. Intrarenal Ang II content in H/S + Ang II was significantly greater than H/S + Sham (435 +/- 153 vs. 65 +/- 14 fmol/g). Ang II infusion significantly increased UAGT (4.0 +/- 0.5 vs. 1.0 +/- 0.2 nmol Ang I/day by radioimmunoassay of generated Ang I; 57 +/- 15 vs. 14 +/- 2 densitometric units by Western blotting analysis) compared to Sham. UAGT by radioimmunoassay was highly correlated with kidney Ang II content (r=0.79); but not with plasma Ang II concentration (r=0.20).Conclusions: These data demonstrate that chronic Ang II infusion increases urinary excretion rate of angiotensinogen, and suggest that UAGT provides a specific index of intrarenal angiotensinogen production in Ang II-dependent hypertension. [ABSTRACT FROM AUTHOR]

Early diabetes mellitus stimulates proximal tubule renin mRNA expression in the rat. Background. Enhanced intrarenal angiotensin II (Ang II) activity may contribute to diabetic nephropathy. The proximal tubule is a proposed site of significant intrarenal Ang II production. We determined the effect of early diabetes on mRNA expression of components of the proximal tubule renin-angiotensin system. Methods. Three groups of male Sprague-Dawley rats were studied after two weeks: (1 ) control (C), (2 ) streptozotocin-induced diabetes (STZ), and (3 ) STZ-induced diabetes, with normoglycemia maintained by insulin implants (STZ-I). Competitive reverse transcription-polymerase chain reaction was used to assay mRNA for renin, angiotensinogen, and angiotensin-converting enzyme in suspensions of proximal tubules; plasma and kidney levels of Ang II were measured by radioimmunoassay, and Western analysis of Ang II subtype 1 (AT1 ) receptors was performed. Results. STZ rats tended to have increased plasma and intrarenal levels of Ang II compared with C and STZ-I rats. In proximal tubules, mRNA for renin was significantly increased in STZ rats, with reversal to control values in STZ-I rats (C, 2432 ± 437 vs. STZ, 5688 ± 890 fg/0.25 μg RNA, P < 0.05 vs. C, N = 9, vs. STZ-I, 1676 ± 376 fg/0.25 μg RNA, P = NS vs. C). In STZ rats, the AT1 receptor antagonist losartan caused a further fivefold increase in proximal tubule renin mRNA, associated with proximal tubular renin immunostaining. STZ had no significant effect on mRNA expression for angiotensinogen or angiotensin-converting enzyme in proximal tubules. By Western blot analysis, cortical and proximal tubule AT1 receptor protein expression was significantly decreased in STZ rats. Conclusions. These data suggest activation of the proximal tubule renin-angiotensin system in early STZ diabetes, mediated at least partly by enhanced expression of renin mRNA. Increased local... [ABSTRACT FROM AUTHOR]

Plasminogen activator inhibitor-1 expression is regulated by the angiotensin type 1 receptor in vivo. Background. The fibrinolytic system plays an important role in degrading fibrin-rich thrombi and in vascular and tissue remodeling. Elevated levels of plasminogen activator inhibitor-1 (PAI-1) can reduce the efficiency of the endogenous fibrinolytic system. Angiotensin (Ang) has been shown to regulate PAI-1 expression via the Ang type 1 (AT1) receptor in some tissues and via the AT4 receptor in cultured endothelium. The purpose of this study was to examine the tissue-specific pattern of PAI-1 expression in response to infusion of Ang II in vivo. Methods. Adult male Sprague-Dawley rats (N = 5 in each group) were treated with four hours of intravenous infusions of Ang II or vehicle control while mean arterial pressure (MAP) was monitored: group 1, 600 ng/kg/min Ang II; group 2, Ang II + 10 mg/kg of the AT1 receptor antagonist (AT1RA) L158-809 q2 hour; group 3, Ang II + 0.01 to 0.1 mg/kg hydralazine as required to maintain normal blood pressure; and group 4, saline-infused controls. After infusion, tissue was harvested for Northern blotting, immunohistochemical analysis, and in situ hybridization. Results. In group 1, Ang II infusion increased MAP from 105 ± 8 to 160 ± 9 mm Hg (mean ± SE, P < 0.01). Ang II induced increased expression of PAI-1 mRNA in all tissues examined from 5.1-fold in the heart, 9.7-fold in the kidney, 10.0-fold in the aorta, and up to 30.0-fold in the liver (all P < 0.01 vs. control). While both AT1RA (group 3) and hydralazine (group 4) prevented Ang II-induced elevation in blood pressure, the Ang II-dependent expression of PAI-1 mRNA was reduced by only AT1 receptor blockade. Conclusions. We conclude that in the rat, PAI-1 is induced in a variety of tissues by Ang II directly through the AT1 receptor, independent of its effects on blood pressure. [ABSTRACT FROM AUTHOR]

Renoprotective effects of angiotensin II receptor blockade in type 1 diabetic patients with diabetic nephropathy. Background. Angiotensin I-converting enzyme (ACE) inhibitors reduce angiotensin II formation and induce bradykinin accumulation. Animal studies suggest that bradykinin may play a role for the effects of ACE inhibition on blood pressure and kidney function. Therefore, we compared the renal and hemodynamic effects of specific intervention in the renin-angiotensin system by blockade of the angiotensin II subtype-1 receptor to the effect of ACE inhibition. Methods. A randomized, double-blind, cross-over trial was performed in 16 type 1 diabetic patients (10 men), age 42 ± 2 years (mean ± sem). The study consisted of five periods, each lasting two months. The patients received losartan 50 mg, losartan 100 mg, enalapril 10 mg, enalapril 20 mg, and placebo in random order. At the end of each period, albuminuria, 24-hour blood pressure, and glomerular filtration rate (GFR) were determined. Results. Both doses of losartan and enalapril reduced albuminuria (P < 0.05) and mean arterial blood pressure (MABP; P < 0.05), whereas GFR remained stable. Albuminuria was reduced by 33% (95% CI, 12 to 51) on losartan 50 mg, 44% (95% CI, 26 to 57) on losartan 100 mg, 45% (95% CI, 23 to 61) on enalapril 10 mg, and 59% (95% CI, 39 to 72) on enalapril 20 mg, and MABP fell by 9 ± 2, 8 ± 2, 6 ± 3, and 11 ± 3 mm Hg (mean ± sem), respectively. No significant differences were found between the effects of losartan 100 mg and enalapril 20 mg. HbA1C and sodium intake remained unchanged throughout the study, whereas a significant rise in serum potassium occurred during ACE inhibition. Conclusion. The angiotensin II subtype 1 receptor antagonist, losartan, reduces albuminuria and MABP similar to the effect of ACE inhibition. These results indicate that the reduction in albuminuria and blood pressure during ACE inhibition is primarily... [ABSTRACT FROM AUTHOR]

Renal function in the AT1A receptor knockout mouse during normal and volume-expanded conditions. Background. Genetically altered mice lacking the AT1A angiotensin II (Ang II) receptor were used to examine the role of AT1A receptors in regulating renal hemodynamics, sodium excretion, glomerulotubular balance, and Ang II levels in plasma and kidney during normal and volume-expanded conditions. Methods. AT1A receptor-deficient mice and their wild-type controls were anesthetized with inactin and ketamine, and were prepared to allow intravenous infusions of solutions and measurements of aortic pressure and urine collections. Inulin and para-aminohippurate (PAH) solutions were infused intravenously for clearance determinations under conditions of euvolemia (2.5 μl/min infusion of isotonic saline) or volume-expansion conditions (12.5 μl/min). After three 30-minute urine collections, blood samples were collected, and kidneys were harvested. Plasma and kidney Ang II measurements were made by radioimmunoassay. Results. In the euvolemic state, mean arterial pressures (MAPs) were significantly lower in the AT1A receptor-deficient mice (68 ± 4 mm Hg) compared with wild-type controls (89 ± 3 mm Hg). Despite the lower MAP, the glomerular filtration rate (GFR), renal plasma flow (RPF), absolute sodium excretion, and fractional sodium excretion were not significantly different between wild-type and AT1A -/- mice. Volume expansion did not alter MAP in wild-type mice, but significantly increased MAP in the AT1A -/- mice (68 ± 4 to 83 ± 5 mm Hg). Similar increases in GFR, RPF, absolute sodium excretion, and fractional sodium excretion in AT1A +/+ and AT1A -/- mice were observed. Glomerulotubular balance was not disrupted by the absence of AT1A receptors. During euvolemia, plasma Ang II concentrations were significantly higher in the... [ABSTRACT FROM AUTHOR]

Induction of albuminuria in mice: Synergistic effect of two monoclonal antibodies directed to different domains of aminopeptidase A. Background. Aminopeptidase A is an enzyme that is present on podocytes and is involved in the degradation of angiotensin II. In previous studies in mice, we administered single monoclonal antibodies directed against aminopeptidase A. We observed that only monoclonal antibodies that inhibited aminopeptidase A enzyme activity caused albuminuria. Methods. In this study, the effects of the combined injections of two monoclonal anti-aminopeptidase A antibodies (mAbs) were studied, using a combination of anti-aminopeptidase A mAbs that were directed against two different domains involved in the aminopeptidase A enzyme activity (ASD-3 or ASD-37) and an anti-aminopeptidase A mAb not related to the enzyme active site (ASD-41). Results. An injection of the combinations ASD-3/37 (total 4 mg, 1:1 ratio) and ASD-37/41 (total 4 mg, 1:1 ratio) in doses that do not cause albuminuria when given alone (4 mg) induced massive albuminuria at day 1 after injection. The combination ASD-3/41 had no effect. This albuminuria was not dependent on systemic immune mediators of inflammation and could not merely be related to a blockade of aminopeptidase A enzyme activity. However, a correlation was observed between the induction of albuminuria and the aggregation of the mAbs injected and aminopeptidase A on the podocytes. An injection of the combinations ASD-3/37 or ASD-37/41 did not cause an increase in systemic blood pressure. The treatment with a combination of enalapril and losartan lowered blood pressure (53 ± 10 vs. 90 ± 3 mm Hg in untreated mice) and reduced the acute albuminuria by 55% (11,145 ± 864 vs. 24,517 ± 2448 μg albumin/18 hr in untreated mice). However, similar effects were observed using triple therapy. Therefore, the reduction of albuminuria by the combined treatment of enalapril/losartan seems to be the consequence... [ABSTRACT FROM AUTHOR]

Impact of gender on the renal response to angiotensin II. Background. It is clear that women with renal disease progress to end stage at a slower rate than do men. We hypothesized that this protection may result from gender-mediated differences in responses to angiotensin II (Ang II), which has known hemodynamic effects that are thought to promote renal disease progression. We examined sex differences in renin-angiotensin system (RAS) function by measuring renal hemodynamic function and circulating plasma components of the RAS at baseline and in response to graded infusions of Ang II. Methods. We studied two groups of normal healthy subjects, 24 men and 24 women, mean age 28 ± 1 years, ingesting a controlled sodium and protein diet. We examined baseline concentrations of angiotensin converting enzyme, plasma renin activity, Ang II, and aldosterone. Inulin and paraaminohippurate clearance techniques were used to estimate effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) at baseline and in response to graded Ang II infusion (0.5, 1.5, and 2.5 ng/kg/min). Results. Mean baseline values for mean arterial pressure and aldosterone were lower in women, whereas values for plasma Ang II, GFR, ERPF, and filtration fraction (FF) did not differ. In response to Ang II, both groups exhibited a similar increase in mean arterial pressure and a decline in ERPF. GFR was maintained during Ang II infusion only in men, resulting in an augmentation of FF. In women, GFR declined in parallel with ERPF, and the FF response was significantly blunted. 17β-Estradiol plasma concentrations influenced the ERPF response to Ang II infusion, with higher levels predicting a blunting of the decrease. The GFR response was not affected. Conclusions. The renal microcirculation in sodium-replete women may respond differently to Ang II than that of men, with the female sex predicting a lesser augmentation of FF and possibly a blunted increase in intraglomerular pressure.... [ABSTRACT FROM AUTHOR]

Regulation of human renin gene promoter activity: A new negative regulatory region determines the responsiveness to TNFα. Background . The renin-angiotensin system has been known to regulate blood pressure and body fluid homeostasis. Several lines of evidence have shown that renin gene expression and release are up-regulated by β-adrenergic stimulation, sodium depletion, and angiotensin converting enzyme inhibition, but down-regulated by cytokines. To further characterize the human renin gene (hREN) promoter structure, its regulation, and to identify an appropriate cell system for study, we examined five cell lines and investigated drug effects on the hREN promoter expression. Methods. Using the hREN-luciferase reporter gene constructs in the DNA transfection assays, approximately 5 kb of the hREN 5′ flanking region was assessed for promoter activity in five different cell lines. Regulation of the hREN promoter activity was investigated using Y-1 adrenal cells that were transfected with the hREN-luciferase DNA and were treated with forskolin, calcium ionophore A23187, phorbol ester, angiotensin II (Ang II), or cytokines. Results. Transient transfection analysis showed that the 5 kb hREN 5′ flanking DNA alone was able to confer significant promoter activity in Y-1 adrenal cells. In transfected Y-1 cells, luciferase reporter expression was induced by forskolin, suppressed by the calcium ionophore A23187, and phorbol ester in a dose-dependent manner, but was unaffected by angiotensin II (Ang II). However, when Y-1 reporter cells were transfected with human angiotensin II receptor type 1 (AT1) cDNA, hREN promoter activity was dose-dependently down-regulated by Ang II, which was blockable by losartan, an AT1-selective antagonist. Further studies also showed that hREN promoter activity in Y-1 cells was selectively down-regulated by TNFα. Deletion of the hREN promoter sequences between position -3916 and -2822 not only enhanced hREN... [ABSTRACT FROM AUTHOR]

Abnormal regulation of proximal tubule renin mRNA in the Dahl/Rapp salt-sensitive rat. Background. The precise pathogenesis of salt-sensitive hypertension in the Dahl rat is unknown. Abnormalities in renal hemodynamics and NaCl handling have been implicated, and may relate to changes in the activity of the intrarenal renin-angiotensin system. Methods. Circulating, juxtaglomerular and intrarenal (glomerular and proximal tubular) renin were studied in Dahl/Rapp salt-sensitive and salt-resistant rats fed with a normal (0.5%) or high (4%) NaCl diet. Circulating and juxtaglomerular renin were assessed by measurement of plasma renin activity and renin secretory rates. Glomerular and proximal tubular renin mRNA were assessed by microdissection and quantitative competitive RT-PCR. Results . Circulating and juxtaglomerular renin were suppressed by high dietary NaCl in salt-sensitive rats (plasma renin activity, 0.5%, 10.9 ± 0.7 vs. 4%, 7.9 ± 0.3 ng/ml/hr, P < 0.05; renin secretory rate, 0.5% 220 ± 32 vs. 4%, 58 ± 5 ng/mg/hr, P < 0.05). Glomerular renin mRNA was also suppressed by the higher salt diet in salt-sensitive animals (0.5%, 411 ± 84 vs. 4%, 67 ± 22 × 103 copies/glomerulus, P < 0.05). In contrast, proximal tubular renin was not suppressed by a high NaCl diet in salt-sensitive animals (0.5%, 13.9 ± 2.7 vs. 4%, 12.1 ± 3.6 × 103 copies/mm tubule, P = NS), but was suppressed in salt-resistant rats (0.5%, 9.5 ± 2.8 vs. 4%, 3.2 ± 1.2 × 103 copies/mm, P < 0.05). Conclusions. Failure to suppress proximal tubular renin in response to high dietary NaCl may result in increased local generation of angiotensin II and enhanced proximal tubular NaCl absorption, and thereby contribute to the generation of salt sensitive hypertension. [ABSTRACT FROM AUTHOR]

A new model of progressive diabetic renal disease in the transgenic (mRen-2)27 rat (TGR). Background. The tissue renin-angiotensin system (RAS) may modulate the structural and functional changes that occur in the diabetic kidney. Methods. Hypertensive transgenic (mREN-2)27 rat (TGR) that exhibit increased tissue renin expression were administered streptozotocin (STZ, diabetic) or citrate buffer (non-diabetic) at six weeks of age, and sacrificed 4 and 12 weeks later. Further groups were treated for 12 weeks post-STZ or vehicle with the angiotensin converting enzyme inhibitor, perindopril. Comparisons were made with 18-week-old non-diabetic and diabetic spontaneously hypertensive rats (SHR). Results. In diabetic TGR, the most florid lesion was seen after 12 weeks of STZ, with kidneys exhibiting vacuolated tubules, hylanized arterioles, medullary fibrosis and necrosis and severe glomerulosclerosis. In contrast, only mild glomerulosclerosis was seen in non-diabetic TGR and diabetic SHR. Glomerular filtration rate was increased after four weeks of diabetes in TGR and 12 weeks of diabetes in SHR, but declined by greater than 50% after 12 weeks of diabetes in TGR. In both TGR and SHR, diabetes increased albuminuria but did not modify systolic blood pressure. Renal renin content increased progressively in diabetic TGR, and this was associated with increased renin immunolabeling in the juxtaglomerular apparatus (JGA) and the appearance of renin in proximal convoluted tubules. In contrast, renal renin content and JGA renin immunolabeling were unchanged in diabetic SHR. Perindopril attenuated renal pathology, improved renal function and abolished proximal tubular renin immunolabeling in diabetic TGR. Conclusions. This is the first report of a diabetic rodent model developing rapid onset renal impairment. Furthermore, this study suggests a role for an activated renal RAS in the acceleration of diabetic renal disease and confirms the benefit of drugs that inhibit this system. [ABSTRACT FROM AUTHOR]

The role of the circulating renin-angiotensin system (RAS) in regulating systemic blood pressure and sodium balance is well established. More recently, researchers have turned their focus to the local generation of angiotensin II (Ang II) in specific tissues. Matsusaka et al. revisit the renal RAS and provide evidence that liver-derived angiotensinogen (AGT) is a major determinant of renal Ang II levels in a model of podocyte injury. [ABSTRACT FROM AUTHOR]

Lai et al. provide important new information regarding the interaction between the sympathetic and renin–angiotensin systems in the regulation of glomerular afferent arteriolar contractility. Their study demonstrates a calcium-independent enhanced contractile response to angiotensin II following norepinephrine administration. The interplay between the norepinephrine- and angiotensin II–stimulated pathways could potentially be important in physiological as well as pathophysiological situations with increased sympathetic nervous system activity, such as hypertension. [ABSTRACT FROM AUTHOR]

Vitamin D receptor (VDR) activation has a beneficial influence on the progression of experimental renal insufficiency, and reduced renal tissue renin expression may play a role in this process. Freundlich and co-workers now report that VDR activation also suppresses the expression of angiotensinogen, angiotensin II type 1 receptor, and renin receptor in the kidneys of 5/6 nephrectomized rats, effects associated with reduced blood pressure and urinary protein excretion and with alleviated renal tissue damage.Kidney International (2008) 74, 1371–1373. doi:10.1038/ki.2008.424 [ABSTRACT FROM AUTHOR]