Angiotensin converting enzyme-independent angiotensin ii production by chymase is up-regulated in the ischemic kidney in renovascular hypertension

Angiotensin II control of regional haemodynamics in rats with aortocaval fistula

NEW FINDINGS

What is the central question of this study? Hyperdynamic circulation because of arteriovenous fistula results in reduction of blood flow to organs but is a model of low circulatory resistance with activated renin-angiotensin system. The aim was to determine contributions of different subtypes of angiotensin II receptors to regional blood flow and vascular conductance in a hyperdynamic circulatory state. What is the main finding and its importance? The renin-angiotensin system plays a pivotal role in control of regional blood flow in animals with arteriovenous fistula and makes a major contribution to the maintenance of normal arterial blood pressure. In this hyperdynamic circulatory state model, angiotensin II type 1 receptors predominated in regulating regional haemodynamics. Regional perfusion is reduced and the renin-angiotensin system activated in rats with aortocaval fistula. The effects of captopril (angiotensin-converting enzyme inhibitor), losartan (angiotensin II type 1 receptor antagonist) and PD 123319 (angiotensin II type 2 receptor antagonist) on regional blood flow and vascular conductance were assessed in rats with aortocaval fistula and sham-operated rats. Control of blood flow and vascular conductance by angiotensin II was evaluated by serial bolus injections of captopril, losartan and PD 123319 in anaesthetized rats. In rats with fistula, PD 123319 significantly decreased, whereas captopril and losartan increased, mesenteric blood flow. The decrease in mesenteric blood flow induced by PD 123319 was significantly greater in rats with fistula compared with sham operation. Captopril and PD 123319 significantly decreased renal blood flow compared with losartan, which increased it. In sham-operated rats, captopril and losartan significantly increased, whereas PD 123319 decreased, mesenteric and renal conductance. In rats with fistula, captopril and losartan significantly increased, whereas PD 123319 decreased, mesenteric conductance. The significant increase produced by losartan on mesenteric conductance was greater in rats with fistula compared with sham operation. PD 123319 produced a significantly greater decrease in renal conductance of rats with aortocaval fistula compared with sham-operated rats. Captopril, losartan and PD 123319 did not significantly affect perfusion in the hindquarter in rats with fistula or sham-operated. The renin-angiotensin system is more active in the control of regional haemodynamics in rats with aortocaval fistula and acts as a mechanism of maintaining normal arterial blood pressure in these animals. In rats with fistula, angiotensin II type 1 receptors predominate in regulating regional haemodynamics.

Effects of chymostatin, a chymase inhibitor, on blood pressure, plasma and tissue angiotensin II, renal haemodynamics and renal excretion in two models of hypertension in the rat

NEW FINDINGS

What is the central question of this study? We examined, in hypertensive rats, whether the angiotensin-converting enzyme-independent enzymes generating angiotensin II in the tissues modulate blood pressure, peripheral circulation and renal function. What is the main finding and its importance? The results suggest that chymostatin-sensitive enzymes diminish vascular tone in renal and extrarenal vascular beds. Chymase or similar chymostatin-sensitive enzymes have a significant role in the synthesis of angiotensin II in different tissues but do not control blood pressure in the short term, similarly in salt-dependent or Goldblatt-type rat hypertension. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing the angiotensin II content in the kidney. Chymase is presumed to be a crucial enzyme of the non-angiotensin-converting enzyme pathway of angiotensin II (Ang II) generation in tissues, a process involved in vascular remodelling and development of hypertension. We examined the role of chymase in hypertension induced by exposure of uninephrectomized rats to high dietary salt intake (UNX HS) and in the Goldblatt renal artery stenosis (two-kidney, one-clip) model. In acute experiments with anaesthetized rats of either model, chymostatin at 2 mg kg(-1) h(-1) or 0.05% DMSO solvent was infused i.v. Mean arterial blood pressure, heart rate, iliac blood flow (a measure of hindlimb perfusion), total renal blood flow and intrarenal regional perfusion (laser-Doppler technique) were measured continuously, along with the glomerular filtration rate and renal excretion. In both models, chymase blockade distinctly decreased plasma and tissue Ang II without lowering mean blood pressure or consistently altering the other functional parameters measured. Unexpectedly, in Goldblatt hypertensive rats the blockade increased the renal and hindlimb vascular resistances by 51 and 33%, respectively (P < 0.05). In UNX HS hypertensive rats, chymase blockade abolished the solvent-induced decrease in outer medullary blood flow. We conclude that chymase or similar chymostatin-sensitive enzyme(s) has a significant role in the synthesis of Ang II in different tissues but does not participate in short-term control of blood pressure in salt-dependent or Goldblatt-type rat hypertension. In the Goldblatt model, chymase appeared to reduce the renal and hindlimb vascular resistances by an unknown mechanism. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing Ang II content in the kidney.

Angiotensin AT2 receptor agonist prevents salt-sensitive hypertension in obese Zucker rats

High-sodium intake is a risk factor for the pathogenesis of hypertension, especially in obesity. The present study is designed to investigate whether angiotensin type 2 receptor (AT2R) activation with selective agonist C21 prevents high-sodium diet (HSD)-induced hypertension in obese animals. Male obese rats were treated with AT2R agonist C21 (1 mg·kg(-1)·day(-1), oral) while maintained on either normal-sodium diet (NSD; 0.4%) or HSD (4%) for 2 wk. Radiotelemetric recording showed a time-dependent increase in systolic blood pressure in HSD-fed obese rats, being maximal increase (∼27 mmHg) at day 12 of the HSD regimen. C21 treatment completely prevented the increase in blood pressure of HSD-fed rats. Compared with NSD controls, HSD-fed obese rats had greater natriuresis/diuresis and urinary levels of nitrates, and these parameters were further increased by C21 treatment. Also, C21 treatment improved glomerular filtration rate in HSD-fed rats. HSD-fed rats expressed higher level of cortical ANG II, which was reduced to 50% by C21 treatment. HSD feeding and/or C21 treatment had no effects on cortical renin activity and the expression of angiotensin-converting enzyme (ACE) and chymase, which are ANG II-producing enzymes. However, ANG(1-7) concentration and ACE2 activity in the renal cortex were reduced by HSD feeding, and C21 treatment rescued both the parameters. Also, C21 treatment reduced the cortical expression of AT1R in HSD-fed rats, but had no effect of AT2R expression. We conclude that chronic treatment with the AT2R agonist C21 prevents salt-sensitive hypertension in obese rats, and a reduction in the renal ANG II/AT1R and enhanced ACE2/ANG(1-7) levels may play a potential role in this phenomenon.

Diabetic Nephropathy Induced by Increased Ace Gene Dosage Is Associated with High Renal Levels of Angiotensin (1-7) and Bradykinin

Population studies have shown an association between diabetic nephropathy (DN) and insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene (ACE in humans, Ace in mice). The aim was to evaluate the modulation of Ace copies number and diabetes mellitus (DM) on renal RAS and correlate it with indicators of kidney function. Increased number of copies of the Ace gene, associated with DM, induces renal dysfunction. The susceptibility to the development of DN in 3 copies of animals is associated with an imbalance in activity of RAS enzymes leading to increased synthesis of Ang II and Ang-(1-7). Increased concentration of renal Ang-(1-7) appears to potentiate the deleterious effects triggered by Ang II on kidney structure and function. Results also show increased bradykinin concentration in 3 copies diabetic group. Taken together, results indicate that the deleterious effects described in 3 copies diabetic group are, at least in part, due to a combination of factors not usually described in the literature. Thus, the data presented here show up innovative and contribute to understanding the complex mechanisms involved in the development of DN, in order to optimize the treatment of patients with this complication.

Inhibition of phosphodiesterase 5 restores endothelial function in renovascular hypertension

Background

The clipping of an artery supplying one of the two kidneys (2K1C) activates the renin-angiotensin (Ang) system (RAS), resulting in hypertension and endothelial dysfunction. Recently, we demonstrated the intrarenal beneficial effects of sildenafil on the high levels of Ang II and reactive oxygen species (ROS) and on high blood pressure (BP) in 2K1C mice. Thus, in the present study, we tested the hypothesis that sildenafil improves endothelial function in hypertensive 2K1C mice by improving the NO/ROS balance.

Methods

2K1C hypertension was induced in C57BL/6 mice. Two weeks later, they were treated with sildenafil (40 mg/kg/day, via oral) or vehicle for 2 weeks and compared with sham mice. At the end of the treatment, the levels of plasma and intrarenal Ang peptides were measured. Endothelial function and ROS production were assessed in mesenteric arterial bed (MAB).

Results

The 2K1C mice exhibited normal plasma levels of Ang I, II and 1–7, whereas the intrarenal Ang I and II were increased (~35% and ~140%) compared with the Sham mice. Sildenafil normalized the intrarenal Ang I and II and increased the plasma (~45%) and intrarenal (+15%) Ang 1–7. The 2K1C mice exhibited endothelial dysfunction, primarily due to increased ROS and decreased NO productions by endothelial cells, which were ameliorated by treatment with sildenafil.

Conclusion

These data suggest that the effects of sildenafil on endothelial dysfunction in 2K1C mice may be due to interaction with RAS and restoring NO/ROS balance in the endothelial cells from MAB. Thus, sildenafil is a promising candidate drug for the treatment of hypertension accompanied by endothelial dysfunction and kidney disease.

Evidence for an angiotensin-(1-7) neuropeptidase expressed in the brain medulla and CSF of sheep

Angiotensin-(1-7) [Ang-(1-7)] is an alternative product of the brain renin-angiotensin system that exhibits central actions to lower blood pressure and improve baroreflex sensitivity. We previously identified a peptidase that metabolizes Ang-(1-7) to the inactive metabolite product Ang-(1-4) in CSF of adult sheep. This study purified the peptidase 1445-fold from sheep brain medulla and characterized this activity. The peptidase was sensitive to the chelating agents o-phenanthroline and EDTA, as well as the mercury compound p-chloromercuribenzoic acid (PCMB). Selective inhibitors to angiotensin-converting enzyme, neprilysin, neurolysin, and thimet oligopeptidase did not attenuate activity; however, the metallopeptidase agent JMV-390 was a potent inhibitor of Ang-(1-7) hydrolysis (Ki = 0.8 nM). Kinetic studies using (125) I-labeled Ang-(1-7), Ang II, and Ang I revealed comparable apparent Km values (2.6, 2.8, and 4.3 μM, respectively), but a higher apparent Vmax for Ang-(1-7) (72 vs. 30 and 6 nmol/min/mg, respectively; p < 0.01). HPLC analysis of the activity confirmed the processing of unlabeled Ang-(1-7) to Ang-(1-4) by the peptidase, but revealed < 5% hydrolysis of Ang II or Ang I, and no hydrolysis of neurotensin, bradykinin or apelin-13. The unique characteristics of the purified neuropeptidase may portend a novel pathway to influence actions of Ang-(1-7) within the brain. Angiotensin-(1-7) actions are mediated by the AT7 /Mas receptor and include reduced blood pressure, decreased oxidative stress, enhanced baroreflex sensitivity, and increased nitric oxide (NO). Ang-(1-7) is directly formed from Ang I by neprilysin (NEP). We identify a new pathway for Ang-(1-7) metabolism in the brain distinct from angiotensin-converting enzyme-dependent hydrolysis. The Ang-(1-7) endopeptidase (A7-EP) degrades the peptide to Ang-(1-4) and may influence central Ang-(1-7) tone.

Nonclassical renin-angiotensin system and renal function

The renin-angiotensin system (RAS) constitutes one of the most important hormonal systems in the physiological regulation of blood pressure through renal and nonrenal mechanisms. Indeed, dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, including kidney injury, and blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or blockade of the angiotensin type 1 receptor (AT1R) by selective antagonists constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS within the kidney and other tissues that the system is actually composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, water intake, sodium retention, and other mechanisms to maintain blood pressure, as well as increase oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the nonclassical RAS composed primarily of the AngII/Ang III-AT2R pathway and the ACE2-Ang-(1-7)-AT7R axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and reduced oxidative stress. Moreover, increasing evidence suggests that these non-classical RAS components contribute to the therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury, as well as contribute to normal renal function.

Impact of Mast Cell Chymase on Renal Disease Progression

Chymase, a serine protease found in mast cell granules, is released into the interstitium following injury or inflammation. Chymase is the primary ACE-independent pathway of angiotensin II formation, and also functions to activate TGF-beta and other promoters of extracellular matrix degradation, thereby playing a role in tissue remodeling. In the diseased kidney, chymase-containing mast cells markedly increase and their density correlates with tubulointerstitial fibrosis severity. Studies in humans support the pathologic role of chymase in diabetic nephropathy, while animal studies form the basis for the importance of increased chymase-dependent angiotensin II formation in progressive hypertensive, diabetic and inflammatory nephropathies. Moreover, humans with kidney disease express chymase in diseased blood vessels in concordance with significantly elevated plasma chymase levels. Conversely, specific chymase inhibitors attenuate angiotensin II production and renal fibrosis in animal models, suggesting their potential therapeutic benefit in human nephropathy, where chymase-containing mast cells accumulate and contribute to progressive disease.

Antihypertensive effect of long-term oral administration of jellyfish (Rhopilema esculentum) collagen peptides on renovascular hypertension

Antihypertensive effect of long-term oral administration of jellyfish (Rhopilema esculentum) collagen peptides (JCP) on renovascular hypertension rats (RVHs) was evaluated. The systolic blood pressure and diastolic blood pressure of the RVHs were significantly reduced with administration of JCP (p < 0.05), compared with model control group. However, the arterial blood pressure of normal rats showed no significant changes during long-term oral treatment with high dose JCP (p > 0.05). Furthermore, effect of JCP on angiotensin II (Ang II) concentration of plasma had no significance (p > 0.05), but JCP significantly inhibited the Ang II concentration in RVHs’ kidney (p < 0.05). The kidney should be the target site of JCP.

Reciprocal changes in renal ACE/ANG II and ACE2/ANG 1-7 are associated with enhanced collecting duct renin in Goldblatt hypertensive rats

Alterations in the balance between ANG II/ACE and ANG 1-7/ACE2 in ANG II-dependent hypertension could reduce the generation of ANG 1-7 and contribute further to increased intrarenal ANG II. Upregulation of collecting duct (CD) renin may lead to increased ANG II formation during ANG II-dependent hypertension, thus contributing to this imbalance. We measured ANG I, ANG II, and ANG 1-7 contents, angiotensin-converting enzyme (ACE) and ACE2 gene expression, and renin activity in the renal cortex and medulla in the clipped kidneys (CK) and nonclipped kidneys (NCK) of 2K1C rats. After 3 wk of unilateral renal clipping, systolic blood pressure and plasma renin activity increased in 2K1C rats (n = 11) compared with sham rats (n = 9). Renal medullary angiotensin peptide levels were increased in 2K1C rats [ANG I: (CK = 171 ± 4; NCK = 251 ± 8 vs. sham = 55 ± 3 pg/g protein; P < 0.05); ANG II: (CK = 558 ± 79; NCK = 328 ± 18 vs. sham = 94 ± 7 pg/g protein; P < 0.001)]; and ANG 1-7 levels decreased (CK = 18 ± 2; NCK = 19 ± 2 pg/g vs. sham = 63 ± 10 pg/g; P < 0.001). In renal medullas of both kidneys of 2K1C rats, ACE mRNA levels and activity increased but ACE2 decreased. In further studies, we compared renal ACE and ACE2 mRNA levels and their activities from chronic ANG II-infused (n = 6) and sham-operated rats (n = 5). Although the ACE mRNA levels did not differ between ANG II rats and sham rats, the ANG II rats exhibited greater ACE activity and reduced ACE2 mRNA levels and activity. Renal medullary renin activity was similar in the CK and NCK of 2K1C rats but higher compared with sham. Thus, the differential regulation of ACE and ACE2 along with the upregulation of CD renin in both the CK and NCK in 2K1C hypertensive rats indicates that they are independent of perfusion pressure and contribute to the altered content of intrarenal ANG II and ANG 1-7.

Major role for ACE-independent intrarenal ANG II formation in type II diabetes

Combination therapy of angiotensin-converting enzyme (ACE) inhibition and AT(1) receptor blockade has been shown to provide greater renoprotection than ACE inhibitor alone in human diabetic nephropathy, suggesting that ACE-independent pathways for ANG II formation are of major significance in disease progression. Studies were performed to determine the magnitude of intrarenal ACE-independent formation of ANG II in type II diabetes. Although renal cortical ACE protein activity [2.1 +/- 0.8 vs. 9.2 +/- 2.1 arbitrary fluorescence units (AFU) x mg(-1) x min(-1)] and intensity of immunohistochemical staining were significantly reduced and ACE2 protein activity (16.7 +/- 3.2 vs. 7.2 +/- 2.4 AFU x mg(-1) x min(-1)) and intensity elevated, kidney ANG I (113 +/- 24 vs. 110 +/- 45 fmol/g) and ANG II (1,017 +/- 165 vs. 788 +/- 99 fmol/g) levels were not different between diabetic and control mice. Afferent arteriole vasoconstriction due to conversion of ANG I to ANG II was similar in magnitude in kidneys of diabetic (-28 +/- 3% at 1 microM) and control (-23 +/- 3% at 1 microM) mice; a response completely inhibited by AT(1) receptor blockade. In control kidneys, afferent arteriole vasoconstriction produced by ANG I was significantly attenuated by ACE inhibition, but not by serine protease inhibition. In contrast, afferent arteriole vasoconstriction produced by intrarenal conversion of ANG I to ANG II was significantly attenuated by serine protease inhibition, but not by ACE inhibition in diabetic kidneys. In conclusion, there is a switch from ACE-dependent to serine protease-dependent ANG II formation in the type II diabetic kidney. Pharmacological targeting of these serine protease-dependent pathways may provide further protection from diabetic renal vascular disease.

Angiotensin I is largely converted to angiotensin (1-7) and angiotensin (2-10) by isolated rat glomeruli

Intraglomerular renin-angiotensin system enzyme activities have been examined previously using glomerular lysates and immune-based assays. However, preparation of glomerular extracts compromises the integrity of their anatomic architecture. In addition, antibody-based assays focus on angiotensin (Ang) II detection, ignoring the generation of other Ang I-derived metabolites, some of which may cross-react with Ang II. Therefore, our aim was to examine the metabolism of Ang I in freshly isolated intact glomeruli using matrix-assisted laser desorption ionization time of flight mass spectrometry as an analytic method. Glomeruli from male Sprague-Dawley rats were isolated by sieving and incubated in Krebs buffer in the presence of 1 micromol/L of Ang I for 15 to 90 minutes, with or without various peptidase inhibitors. Peptide sequences were confirmed by matrix-assisted laser desorption ionization time of flight tandem mass spectrometry or linear-trap-quadrupole mass spectrometry. Peaks were quantified using customized valine-(13)C(.15)N-labeled peptides as standards. The most prominent peaks resulting from Ang I cleavage were 899 and 1181 m/z, corresponding with Ang (1-7) and Ang (2-10), respectively. Smaller peaks for Ang II, Ang (1-9), and Ang (3-10) also were detected. The disappearance of Ang I was significantly reduced during inhibition of aminopeptidase A or neprilysin. In contrast, captopril did not alter Ang I degradation. Furthermore, during simultaneous inhibition of aminopeptidase A and neprilysin, the disappearance of Ang I was markedly attenuated compared with all of the other conditions. These results suggest that there is prominent intraglomerular conversion of Ang I to Ang (2-10) and Ang (1-7), mediated by aminopeptidase A and neprilysin, respectively. Formation of these alternative Ang peptides may be critical to counterbalance the local actions of Ang II. Enhancement of these enzymatic activities may constitute potential therapeutic targets for Ang II-mediated glomerular diseases.

The importance of the intrarenal renin-angiotensin system

Evidence suggests that virtually every organ system in the human body possesses a local renin-angiotensin system (RAS). These local systems seem to be independently regulated and compartmentalized from the plasma circulation, perhaps with the exception of the vascular endothelial system, which is responsible for maintaining physiological plasma levels of RAS components. Among these local RASs, the kidney RAS--the focus of this Review--seems to be of critical importance for the regulation of blood pressure and salt balance. Indeed, overactivation of the intrarenal RAS in certain disease states constitutes a pathogenic mechanism that leads to tissue injury, proliferation, fibrosis and ultimately, end-organ damage. Intrarenal levels of angiotensin peptides are considerably higher than those in plasma or any other organ tissue. Moreover, the kidney has a unique capacity to degrade angiotensin peptides, perhaps to maintain its intrinsic homeostasis. Interestingly, each local RAS has a distinct enzymatic profile resulting in different patterns of angiotensin fragment generation in different tissues. A better understanding of the autocrine and paracrine mechanisms involved in the renal RAS and other local RASs might direct future organ-specific therapy.

Effects of maternal undernutrition on renal angiotensin II and chymase in hypertensive offspring

Intrauterine growth restriction (IUGR) can program the future development of hypertension in adulthood. The renin-angiotensin system has been reported to play a role in IUGR-induced hypertension. The aims of this study were to investigate the effects of IUGR on renal angiotensin-converting enzyme (ACE), angiotensin II (Ang II) and chymase in IUGR-induced hypertension. Timed pregnant Sprague-Dawley rats received 50% rations of control food intakes from days 15 to 21 of gestation. Control rats received regular food throughout the pregnancies. Arterial blood pressure and glomerular number were measured and immunohistochemical studies were performed on kidney tissues in adult male offspring at 16 weeks of age. IUGR rats exhibited significantly lower body and kidney weights and reduced number of glomeruli when compared with control rats. IUGR rats had significantly higher systolic blood pressure than control rats. Immunoreactivity of ACE was comparable between control and IUGR rats whereas immunoreactivities of chymase and Ang II were significantly higher in IUGR rats than in control rats. In conclusion, immunohistochemical studies document up-regulation of ACE-independent Ang II and chymase in IUGR kidney and indicate that overactivity of chymase may result in increased intrarenal Ang II production, which could contribute to the development of hypertension in intrauterine undernourished rats.

Renin-Angiotensin system - considerations for hypertension and kidney

The kidneys play a fundamental role in the long-term control of arterial pressure by regulating sodium balance and extracellular fluid volume. The renin-angiotensin system (RAS) is at the center of the regulation of hypertension and progressive renal injury. It has gradually become clear that not only systemic RAS, but also intrarenal RAS has specific effects in the pathogenesis and progression of hypertension and renal damage. All of the RAS components are exhibited in the kidney and intrarenal angiotensin II (Ang II) is formed by multiple mechanisms. The demonstration of much enhanced levels of Ang II within specific renal compartments points out selective local regulation of Ang II in the kidney, showing that intrarenal Ang II levels are regulated in a way different from circulating Ang II. The importance of the RAS in involving proper nephrogenesis is also well known, and suppression of the RAS during fetal development may play a key role in mediating the structural and physiological changes observed in models of fetal programming of hypertension.

Activation of a local renin angiotensin system in podocytes by glucose

ANG II is a critical mediator of diabetic nephropathy. Pharmacologic inhibition of ANG II slows disease progression beyond what could be predicted by the blood pressure lowering effects alone, suggesting the importance of nonhemodynamic pathways of ANG II in mediating disease. Podocyte injury and loss are cardinal features of diabetic nephropathy. Mounting evidence suggests that the podocyte is a direct target of ANG II-mediated signaling in diabetic renal disease. We have tested the hypothesis that high glucose leads to the activation of a local angiotensin system in podocytes and delineated the underlying pathways involved. Cultured podocytes were exposed to standard glucose (5 mM), high glucose (40 mM), or mannitol as an osmotic control. ANG II levels in cell lysates were measured in the presence or absence of inhibitors of angiotensin-converting enzyme (captopril), chymase (chymostatin), and renin (aliskiren) activity. The effects of glucose on renin and angiotensin subtype 1 receptor expression and protein levels were determined. Exposure to high glucose resulted in a 2.1-fold increase ANG II levels mediated through increased renin activity, as exposure to high glucose increased renin levels and preincubation with Aliskiren abrogated glucose-induced ANG II production. Relevance to the in vivo setting was demonstrated by showing glomerular upregulation of the prorenin receptor in a podocyte distribution early in the course of experimental diabetic nephropathy. Furthermore, high glucose increased angiotensin subtype 1 receptor levels by immunofluorescence and Western blot. Taken together, the resultant activation of a local renin angiotensin system by high glucose may promote progressive podocyte injury and loss in diabetic nephropathy.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Intratubular Renin-Angiotensin System in Hypertension

It is well recognized that the renin-angiotensin system plays an important role in the regulation of arterial pressure and sodium homeostasis. Recent years, many studies have shown that local tissue angiotensin II levels are differentially regulated and cannot be explained on the basis of circulating concentrations. All of the components needed for angiotensin II generation are present within the various compartments in the kidney including the renal interstitium and the tubular network. The cascade of the renin-angiotensin system demonstrates three major possible sites for the pharmacological interruption of the renin-angiotensin system: the interaction of renin with its substrate, angiotensinogen, the angiotensin converting enzyme, and angiotensin II type 1 receptors. This brief article will focus on the role of the intratubular renin-angiotensin system in the pathophysiology of hypertension and the responses to the renin-angiotensin system blockade by renin inhibitors, angiotensin converting enzyme inhibitors and angiotensin II type 1 receptor blockers.