Regulation of intrarenal angiotensin II in hypertension

Translational studies on augmentation of intratubular renin-angiotensin system in hypertension

Various models of experimental hypertension and clinical examples of increased renin formation from a stenotic kidney or a juxtaglomerular cell tumor have shown that increased circulating angiotensin II (Ang II) stimulates the intrarenal/intratubular renin–angiotensin system (RAS) that elicits renal vasoconstriction, enhanced tubular sodium reabsorption, and progressive development of hypertension and renal injury. The enhanced intrarenal Ang II activity is due to both receptor-mediated Ang II uptake and Ang II type 1 (AT1) receptor–mediated stimulation of renal angiotensinogen (AGT) mRNA and protein by proximal tubule cells. The increased AGT secretion leads to local formation of Ang II and spillover of AGT into the distal nephron segments as reflected by increased AGT excretion in the urine, which provides an index of intrarenal RAS activity. In clinical studies, increased urinary excretion of AGT has been demonstrated in hypertension, type 1 and type 2 diabetes mellitus, and several types of chronic kidney diseases. In addition, renin secretion from principal cells of the collecting ducts is increased by AT1 receptor activation and acts on AGT from the proximal tubule to form more Ang I. Renin and/or (pro)renin activity is enhanced by binding to the (pro)renin receptor (PRR) on intercalated cells or secreted as soluble PRR contributing further to AGT cleavage, thus making more substrate available for Ang II conversion by local angiotensin-converting enzyme. The augmented intratubular Ang II concentrations together with elevated renal interstitial Ang II concentrations contribute to sustained stimulation of sodium reabsorption, vasoconstriction, development of hypertension, and progressive renal injury and fibrosis.

Oxidative stress/angiotensinogen/renin-angiotensin system axis in patients with diabetic nephropathy

Although recent studies have proven that renin-angiotensin system (RAS) blockades retard the progression of diabetic nephropathy, the detailed mechanisms of their reno-protective effects on the development of diabetic nephropathy remain uncertain. In rodent models, it has been reported that reactive oxygen species (ROS) are important for intrarenal angiotensinogen (AGT) augmentation in the progression of diabetic nephropathy. However, no direct evidence is available to demonstrate that AGT expression is enhanced in the kidneys of patients with diabetes. To examine whether the expression levels of ROS- and RAS-related factors in kidneys are increased with the progression of diabetic nephropathy, biopsied samples from 8 controls and 27 patients with type 2 diabetes were used. After the biopsy, these patients were diagnosed with minor glomerular abnormality or diabetes mellitus by clinical and pathological findings. The intensities of AGT, angiotensin II (Ang II), 4-hydroxy-2-nonenal (4-HNE), and heme oxygenase-1 (HO-1) were examined by fluorescence in situ hybridization and/or immunohistochemistry. Expression levels were greater in patients with diabetes than in control subjects. Moreover, the augmented intrarenal AGT mRNA expression paralleled renal dysfunction in patients with diabetes. These data suggest the importance of the activated oxidative stress/AGT/RAS axis in the pathogenesis of diabetic nephropathy.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

Glomerular angiotensin-converting enzyme 2 in pediatric IgA nephropathy

BACKGROUND

Angiotensin-converting enzyme (ACE) 2 is a homolog of ACE and is thought to be a potent counter-regulator against ACE activity. However, the role of ACE2 has not been investigated in pediatric patients with IgA nephropathy (IgAN). This study was performed to examine the relationship between ACE2 expression and the development of pediatric IgAN.

METHODS

We performed immunohistochemical analysis of ACE2 and ACE in 39 patients with pediatric IgAN and 14 patients with minor glomerular abnormalities, and elucidated the effects of various cytokines on ACE2 expression in cultured human mesangial cells.

RESULTS

ACE2 expression levels in glomeruli and tubules were positively correlated with the mesangial hypercellularity score, while ACE expression levels in glomeruli and tubules are not. Multiple regression analysis showed that the mesangial hypercellularity score correlated with the ACE2 expression level in glomeruli and the urinary protein-creatinine ratio. In IgAN patients not treated with a renin-angiotensin system blocker, ACE2 expression levels in glomeruli were significantly increased compared to patients with minor glomerular abnormalities. IgAN patients treated with a renin-angiotensin system blocker did not show this increase in ACE2 expression. Furthermore, cultured human MC showed increased ACE2 mRNA and protein after treatment with IL-1β, a pro-inflammatory cytokine in IgAN. In fact, glomerular expressions of IL-1β were remarkably increased in patients with IgAN.

CONCLUSION

These data indicate that ACE2 expression in glomeruli is associated with mesangial hypercellularity in early lesions of pediatric IgAN.

A link between the intrarenal renin angiotensin system and hypertension in autosomal dominant polycystic kidney disease

BACKGROUND/AIMS

Early onset of hypertension and its consequences account for the great majority of deaths in patients with autosomal dominant polycystic kidney disease (ADPKD). Renin-angiotensin system (RAS) components have been shown in ADPKD kidneys independent of systemic RAS. Thus, we examined the urinary angiotensinogen (UAGT) levels as a biomarker of intrarenal RAS status in ADPKD patients with/without hypertension and healthy subjects.

METHODS

Eighty-four ADPKD patients (43 with hypertension and 41 without hypertension) and 40 healthy controls were studied cross-sectionally. Patients with glomerular filtration rate <60 ml/min were excluded from the study. Hypertension was diagnosed with ambulatory blood pressure monitoring. Urinary and plasma concentration of angiotensinogen, spot urine microprotein and creatinine (UCre) levels were recorded for each participant.

RESULTS

UAGT/UCre levels were higher in hypertensive ADPKD patients (23.7 ± 8.4) compared with normotensive ADPKD patients (16.6 ± 5.2) and healthy controls (6.9 ± 3.3; p < 0.001). In univariate analysis, UAGT correlated with systolic blood pressure, diastolic blood pressure (DBP) and proteinuria. The independence of these correlations was analyzed in a regression model, and UAGT was shown to be significantly predicted by proteinuria and DBP.

CONCLUSION

Intrarenal RAS activation which is monitored by UAGT levels clinically may be a harbinger of hypertension and kidney disease in ADPKD patients.

Urinary angiotensinogen as a potential biomarker of severity of chronic kidney diseases

We previously reported that urinary excretion rates of angiotensinogen (AGT) provide a specific index of the activity of the intrarenal renin-angiotensin system in angiotensin II-dependent hypertensive rats. Meanwhile, we have recently developed direct enzyme-linked immunosorbent assays (ELISAs) to measure plasma and urinary AGT in humans. This study was performed to test a hypothesis that urinary AGT levels are enhanced in chronic kidney disease (CKD) patients and correlated with some clinical parameters. Eighty patients with CKD (37 women and 43 men, from 18 to 94 years old) and seven healthy volunteers (two women and five men, from 27 to 43 years old) were included. Plasma AGT levels showed a normal distribution; however, urinary AGT-creatinine ratios (UAGT/UCre) deviated from the normal distribution. When a logarithmic transformation was executed, Log(UAGT/UCre) levels showed a normal distribution. Therefore, Log(UAGT/UCre) levels were used for further analyses. Log(UAGT/UCre) levels were not correlated with age, gender, height, body weight, body mass index, systolic blood pressure, diastolic blood pressure, serum sodium levels, serum potassium levels, urinary sodium-creatinine ratios, plasma renin activity, or plasma AGT levels. However, Log(UAGT/UCre) levels were significantly correlated positively with urinary albumin-creatinine ratios, fractional excretion of sodium, urinary protein-creatinine ratios, and serum creatinine, and correlated negatively with estimated glomerular filtration rate. Log(UAGT/UCre) levels were significantly increased in CKD patients compared with control subjects (1.8801 +/- 0.0885 vs. 0.9417 +/- 0.1048; P = .0024). These data confirmed our earlier report and showed that a new ELISA assay is a valid approach for measuring urinary AGT.

Divergent localization of angiotensinogen mRNA and protein in proximal tubule segments of normal rat kidney

OBJECTIVES

Angiotensinogen in the kidneys is formed primarily in the proximal tubule cells and is secreted into the tubular fluid. Structurally, proximal tubules can be divided into three segments. The first segment, segment 1 (S1) is mainly confined to the pars convoluta, the second segment, segment 2 (S2) comprises the end of pars convoluta, and the third segment, segment 3 (S3) includes the major part of the pars recta. There are some reports describing angiotensinogen localization in kidneys; however, it remains uncertain which proximal tubule segments express angiotensinogen. To determine the detailed localization of angiotensinogen in the three proximal tubule segments, we established multistaining methods using segment-specific protein markers.

METHODS

Using kidneys from Wistar-Kyoto rats, we performed immunohistochemistry and double or triple staining by fluorescence in-situ hybridization and/or immunofluorescence.

RESULTS

Our results show that angiotensinogen mRNA and protein are expressed in the cortex and outer medulla of the normal rat kidney. Angiotensinogen mRNA was hardly detected in S1, detected weakly in S2 and strongly in S3 segments. In contrast, angiotensinogen protein was detected in S1 at high levels and less in S2 and S3 segments.

CONCLUSION

These data indicate divergence of angiotensinogen mRNA transcription and angiotensinogen protein synthesis and metabolism in different segments of the normal rat proximal tubules.

Direct activation of ENaC by angiotensin II: recent advances and new insights

Angiotensin II (Ang II) is the principal effector of the renin-angiotensin-aldosterone system (RAAS). It initiates myriad processes in multiple organs integrated to increase circulating volume and elevate systemic blood pressure. In the kidney, Ang II stimulates renal tubular water and salt reabsorption causing antinatriuresis and antidiuresis. Activation of the RAAS is known to enhance activity of the epithelial Na(+) channel (ENaC) in the aldosterone-sensitive distal nephron. In addition to its well described stimulatory actions on aldosterone secretion, Ang II is also capable of directly increasing ENaC activity. In this brief review, we discuss recent findings about non-classical Ang II actions on ENaC and speculate about its relevance for renal sodium handling.

Real-time electrochemical detection of ATP and H₂O₂ release in freshly isolated kidneys

Extracellular nucleotides such as adenosine-5'-triphosphate (ATP) and reactive oxygen species are essential local signaling molecules in the kidney. However, measurements of changes in the interstitial concentrations of these substances in response to various stimuli remain hindered due to limitations of existing experimental techniques. The goal of this study was to develop a novel approach suitable for real-time measurements of ATP and H₂O₂ levels in freshly isolated rat kidney. Rats were anesthetized and the kidneys were flushed to clear blood before isolation for consequent perfusion. The perfused kidneys were placed into a bath solution and dual simultaneous amperometric recordings were made with the enzymatic microelectrode biosensors detecting ATP and H₂O₂. It was found that basal levels of H₂O₂ were increased in Dahl salt-sensitive (SS) rats fed a high-salt diet compared with SS and Sprague-Dawley rats fed a low-salt diet and that medulla contained higher levels of H₂O₂ compared with cortex in both strains. In contrast, ATP levels did not change in SS rats when animals were fed a high-salt diet. Importantly, angiotensin II via AT₁ receptor induced rapid release of both ATP and H₂O₂ and this effect was enhanced in SS rats. These results demonstrate that ATP and H₂O₂ are critical in the development of salt-sensitive hypertension and that the current method represents a unique powerful approach for the real-time monitoring of the changes in endogenous substance levels in whole organs.

Important aspects of urine sampling for angiotensinogen measurement: time and preservation conditions in healthy individuals

Intrarenal renin-angiotensin system (RAS) plays an important role for the pathogenesis of renal injuries. Experimental studies have demonstrated that angiotensinogen levels in renal tissues reflect the activity of intrarenal RAS. However, dynamics of urinary angiotensinogen have not been investigated in detail. Therefore, we examined the preservation conditions of the measured values of urinary angiotensinogen concentrations and an ultradian rhythm of urinary angiotensinogen excretion in humans. Urine samples were collected from 24 healthy volunteers. The urinary concentrations of angiotensinogen were measured by using ELISA. Two different urine preservation conditions were examined. One cycle of freeze-and-thaw did not change the measured values of urinary angiotensinogen concentrations. Moreover, to keep urine samples at room temperature for 12 hours did not change the measured values of urinary angiotensinogen concentrations. Thus, preservation conditions do not change the measured values of urinary angiotensinogen concentrations. Regarding an ultradian rhythm, blood pressure and the urinary concentrations of angiotensinogen were measured at 09:00, 13:00, and 16:00. The averaged levels of blood pressure were similar over the time. The average of urinary angiotensinogen/creatinine (Cr) ratios was 8.73 ± 1.15 ng/mg Cr at 09:00, 9.53 ± 1.58 ng/mg Cr at 13:00, and 8.58 ± 1.26 ng/mg Cr at 16:00. The urinary angiotensinogen excretion in healthy volunteers does not have an ultradian change during the daytime (P = 0.482). This may be another indication that the intrarenal RAS is independent of the systemic RAS. We have to pay attention to these findings in handling urine samples for measurements of angiotensinogen.

Cardinal Role of the Intrarenal Renin-Angiotensin System in the Pathogenesis of Diabetic Nephropathy

Diabetes mellitus is one of the most prevalent diseases and is associated with increased incidence of structural and functional derangements in the kidneys, eventually leading to end-stage renal disease in a significant fraction of afflicted individuals. The renoprotective effects of renin-angiotensin system (RAS) blockade have been established; however, the mechanistic pathways have not been fully elucidated. In this review article, the cardinal role of an activated RAS in the pathogenesis of diabetic nephropathy (DN) is discussed with a focus on 4 themes: (1) introduction to RAS cascade, (2) intrarenal RAS in diabetes, (3) clinical outcomes of RAS blockade in DN, and (4) potential of urinary angiotensinogen as an early biomarker of intrarenal RAS status in DN. This review article provides a mechanistic rational supporting the hypothesis that an activated intrarenal RAS contributes to the pathogenesis of DN and that urinary angiotensinogen levels provide an index of intrarenal RAS activity.

Reduction of Blood Pressure by AT1 Receptor Decoy Peptides

BACKGROUND

We previously identified the binding of the chaperone protein gamma-aminobutyric acid receptor-associated protein (GABARAP) to a sequence on the carboxy-terminus of the angiotensin II AT1 receptor (AT1R) and showed that this binding enhances AT1R trafficking to the cell surface as well as angiotensin signaling.

METHODS

In this study, we treated sodium-depleted mice with decoy peptides consisting either of a fusion of the cell-penetrating peptide penetratin and the GABARAP/AT1R binding sequence or penetratin fused to a mutated AT1R sequence. We used telemetry to measure blood pressure.

RESULTS

Systolic and diastolic pressure fell during the 24 hours following decoy peptide injection but not after control peptide injection. Active cell-penetrating decoy peptide decreased 24-hour average systolic blood pressure from 129.8 ± 4.7 mmHg to 125.0 ± 6.0 mmHg (mean ± standard deviation). Diastolic blood pressure fell from 99.0 ± 7.1 mmHg to 95.0 ± 9.2 mmHg (n=5). Administration of the control peptide raised systolic blood pressure from 128.7 ± 1.3 mmHg to 131.7 ± 2.9 mmHg and diastolic pressure from 93.9 ± 4.5 mmHg to 95.9 ± 4.2 mmHg (n=5). The decreases in both systolic and diastolic blood pressure after active peptide administration were statistically significant compared to control peptide administration (P<0.05, two-tailed Wilcoxon rank-sum test).

CONCLUSION

These results indicate the physiological and potentially therapeutic relevance of inhibitors of GABARAP/AT1R binding.

Urinary angiotensinogen as a marker of intrarenal angiotensin II activity in adolescents with primary hypertension

BACKGROUND

Experimental and epidemiological studies have demonstrated that urinary angiotensinogen (AGT) is a novel biomarker for the intrarenal activity of the renin-angiotensin system in hypertension (HT). Several large-scale epidemiological studies have shown that an elevated serum uric acid (SUA) level is associated with HT. The aim of our study was to assess urinary AGT excretion and its correlation with SUA level, the lipid profile, and the body mass index (BMI) Z-score in hypertensive adolescents.

METHODS

Participants were divided into two groups: (1) the group with confirmed HT consisting of 55 subjects with primary HT and (2) the reference (R) group consisting of 33 subjects with white-coat HT. A commercial enzyme-linked immunosorbent assay (ELISA) kit was used to determine urinary AGT concentration.

RESULTS

The urinary AGT/creatinine (cr.) ratio in subjects in the HT group was significantly higher than that in the reference group (p < 0.01) and showed a strong positive correlation with SUA (r = 0.47, p < 0.01). The relationship between the AGT/cr. ratio and SUA levels after controlling for age, gender and BMI Z-score continued to show a significant association.

CONCLUSIONS

The most obvious finding to emerge from this study is that in adolescents with primary HT, the increased urinary excretion of AGT correlated with hyperuricemia, although large, multicenter studies are needed to confirm this observation.

The Prorenin and (Pro)renin Receptor: New Players in the Brain Renin-Angiotensin System?

It is well known that the brain renin-angiotensin (RAS) system plays an essential role in the development of hypertension, mainly through the modulation of autonomic activities and vasopressin release. However, how the brain synthesizes angiotensin (Ang) II has been a debate for decades, largely due to the low renin activity. This paper first describes the expression of the vasoconstrictive arm of RAS components in the brain as well as their physiological and pathophysiological significance. It then focus on the (pro)renin receptor (PRR), a newly discovered component of the RAS which has a high level in the brain. We review the role of prorenin and PRR in peripheral organs and emphasize the involvement of brain PRR in the pathogenesis of hypertension. Some future perspectives in PRR research are heighted with respect to novel therapeutic target for the treatment of hypertension and other cardiovascular diseases.

Renal dopamine and angiotensin II receptor signaling in age-related hypertension

Kidneys play a vital role in long-term regulation of blood pressure. This is achieved by actions of many renal and nonrenal factors acting on the kidney that help maintain the body's water and electrolyte balance and thus control blood pressure. Several endogenously formed or circulating hormones/peptides, by acting within the kidney, regulate fluid and water homeostasis and blood pressure. Dopamine and angiotensin II are the two key renal factors that, via acting on their receptors and counterregulating each other's function, maintain water and sodium balance. In this review, we provide recent advances in the signaling cascades of these renal receptors, especially at the level of their cross talk, and discuss their roles in blood pressure regulation in the aging process.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

Urinary angiotensinogen as a novel early biomarker of intrarenal renin-angiotensin system activation in experimental type 1 diabetes

Urinary excretion of albumin (UAlb) is used clinically as a marker of diabetic nephropathy (DN). Although DN was thought to be a unidirectional process, recent studies demonstrated that a large proportion of patients diagnosed with DN reverted to normoalbuminuria. Moreover, despite the normoalbuminuria, one-third of them exhibited reduced renal function even during the microalbuminuric stage. This study was performed to investigate whether urinary angiotensinogen (UAGT) level may serve as a useful marker of the early stage of experimental type 1 diabetes (T1DM). T1DM was induced by a single intraperitoneal injection of streptozotocin. Control mice were injected with citrate buffer. Two days after streptozotocin injection, half of the mice received continuous insulin treatment. Our data showed that UAlb excretion was increased 6 days after streptozotocin injection compared to controls, whereas UAGT excretion was increased at an earlier time point. These increases were reversed by insulin treatment. The UAGT to UAlb ratio was increased in diabetic mice compared to control mice. Furthermore, the increased AGT expression in the kidneys was observed in diabetic mice. These data suggest that UAGT might be useful as a novel early biomarker of activation of the renin-angiotensin system in experimental type 1 diabetes.

The link between the renin-angiotensin-aldosterone system and renal injury in obesity and the metabolic syndrome

Obesity is a risk factor for type 2 diabetes mellitus (DM) and is associated with chronic kidney disease. Activation of the renin-angiotensin-aldosterone system (RAAS) is common in obesity. The RAAS is an important mediator of hypertension. Mechanisms involved in activation of the RAAS in obesity include sympathetic stimulation, synthesis of adipokines in the RAAS by visceral fat, and hemodynamic alterations. The RAAS is known for its role in regulating blood pressure and fluid and electrolyte homeostasis. The role of local/tissue RAAS in specific tissues has been a focus of research. Urinary angiotensinogen (UAGT) provides a specific index of the intrarenal RAAS. Investigators have demonstrated that sex steroids can modulate the expression and activity of the different components of the intrarenal RAAS and other tissues. Our data suggest that obese women without DM and hypertension have significantly higher levels of UAGT than their male counterparts. These differences existed without any background difference in the ratio of microalbumin to creatinine in the urine or the estimated glomerular filtration rate, raising a question about the importance of baseline gender differences in the endogenous RAAS in the clinical spectrum of cardiovascular diseases and the potential utility of UAGT as a marker of the intrarenal RAAS. Animal studies have demonstrated that modifying the amount of angiotensin, the biologically active component of the RAAS, directly influences body weight and adiposity. This article reviews the role of the RAAS in renal injury seen in obesity and the metabolic syndrome.

Involvement of the intrarenal renin-angiotensin system in experimental models of glomerulonephritis

The intrarenal renin-angiotensin system (RAS) has several pathophysiologic functions not only in blood pressure regulation but also in the development of glomerulonephritis (GN). Angiotensin II (Ang II) is the biologically active product of the RAS. Locally produced Ang II induces inflammation, renal cell growth, mitogenesis, apoptosis, migration, and differentiation, regulates the gene expression of bioactive substances, and activates multiple intracellular signaling pathways, leading to tissue damage. Activation of the Ang II type 1 (AT1) receptor pathway results in the production of proinflammatory mediators, cell proliferation, and extracellular matrix synthesis, which facilitates glomerular injury. Previous studies have shown that angiotensin-converting enzyme inhibitors and/or AT1 receptor blockers have beneficial effects in experimental GN models and humans with various types of GN, and that these effects are more significant than their suppressive effects on blood pressure. In this paper, we focus on intrarenal RAS activation in the pathophysiology of experimental models of GN.

The establishment of a primary culture system of proximal tubule segments using specific markers from normal mouse kidneys

The proximal tubule contains the highest expression of angiotensinogen mRNA and protein within the kidney and plays a vital role in the renal renin-angiotensin system. To study the regulation of angiotensinogen expression in the kidney in more detail, the proximal tubule needs to be accurately isolated from the rest of the nephron and separated into its three segments. The purpose of this study was to design a novel protocol using specific markers for the separation of proximal tubule cells into the three proximal tubule segments and to determine angiotensinogen expression in each segment. Kidneys were removed from C57BL/6J mice. The proximal tubules were aspirated from region of a Percoll gradient solution of the appropriate density. The proximal tubule was then separated into its three segments using segment-specific membrane proteins, after which each segment was characterized by a different specific marker (sodium-glucose transporter 2 for Segment 1; carbonic anhydrase IV for Segment 2; ecto-adenosine triphosphatase for Segment 3). The isolation of proximal tubules into three segments was successful, and angiotensinogen mRNA in Segment 2 and 3 and angiotensinogen protein in all three segments were confirmed. This protocol will be helpful for future studies of the detailed mechanisms of the intrarenal renin-angiotensin system.

Renal responses to three types of renin-angiotensin system blockers in patients with diabetes mellitus on a high-salt diet: a need for higher doses in diabetic patients?

OBJECTIVE

Activation of the renal renin-angiotensin system in patients with diabetes mellitus appears to contribute to the risk of nephropathy. Recently, it has been recognized than an elevation of prorenin in plasma also provides a strong indication of risk of nephropathy. This study was designed to examine renin-angiotensin system control mechanisms in the patient with diabetes mellitus.

METHODS

We enrolled 43 individuals with type 2 diabetes mellitus. All individuals were on a high-salt diet to minimize the contribution of the systemic renin-angiotensin system. After an acute exposure to captopril (25 mg), they were randomized to treatment with either irbesartan (300 mg) or aliskiren (300 mg) for 2 weeks.

RESULTS

All agents acutely lowered blood pressure and plasma aldosterone, and increased renal plasma flow and glomerular filtration rate. Yet, only captopril and aliskiren acutely increased plasma renin and decreased plasma angiotensin II, whereas irbesartan acutely affected neither renin nor angiotensin II. Plasma renin and angiotensin II subsequently did increase upon chronic irbesartan treatment. When given on day 14, irbesartan and aliskiren again induced the above hemodynamic, renal and adrenal effects, yet without significantly changing plasma renin. Irbesartan at that time did not affect plasma angiotensin II, whereas aliskiren lowered it to almost zero.

CONCLUSION

The relative resistance of the renal renin response to acute (irbesartan) and chronic (irbesartan and aliskiren) renin-angiotensin system blockade supports the concept of an activated renal renin-angiotensin system in diabetes, particularly at the level of the juxtaglomerular cell, and implies that diabetic patients might require higher doses of renin-angiotensin system blockers to fully suppress the renal renin-angiotensin system.

Reno-endocrinal disorders: A basic understanding of the molecular genetics

The successful management of endocrine diseases is greatly helped by the complete understanding of the underlying pathology. The knowledge about the molecular genetics contributes immensely in the appropriate identification of the causative factors of the diseases and their subsequent management. The fields of nephrology and endocrinology are also interrelated to a large extent. Besides performing the secretory functions, the renal tissue also acts as target organ for many hormones such as antidiuretic hormone (ADH), atrial natriuretic peptides (ANP), and aldosterone. Understanding the molecular genetics of these hormones is important because the therapeutic interventions in many of these conditions is related to shared renal and endocrine functions, including the anemia of renal disease, chronic kidney disease, mineral bone disorders, and hypertension related to chronic kidney disease. Their understanding and in-depth knowledge is very essential in designing and formulating the therapeutic plans and innovating new management strategies. However, we still have to go a long way in order to completely understand the various confounding causative relationships between the pathology and disease of these reno-endocrinal manifestations.

Renal inflammation, autoimmunity and salt-sensitive hypertension

1. The present article reviews the role of immune-competent cells infiltrating the kidney and their association with oxidative stress and renal angiotensin activity in the development of salt-sensitive hypertension. 2. We discuss changes in the pressure-natriuresis relationship resulting from renal inflammation and its improvement resulting from immunosuppressive treatment. 3. The potential role of T-cell-driven reactivity in sustaining the renal inflammation is examined in the light of accumulating evidence of autoimmune mechanisms in experimental and clinical hypertension.

Exosomes and the kidney: prospects for diagnosis and therapy of renal diseases

Exosomes are 40-100 nm membrane vesicles secreted into the extracellular space by numerous cell types. These structures can be isolated from body fluids including urine and plasma. Exosomes contain proteins, mRNAs, miRNAs, and signaling molecules that reflect the physiological state of their cells of origin and consequently provide a rich source of potential biomarker molecules. Aside from diagnostic uses, exosome-mediated transfer of proteins, mRNAs, miRNAs, and signaling molecules offer the promise that they may be used for therapeutic purposes. In this review, we integrate new knowledge about exosomes from outside the field of nephrology with recent progress by renal researchers in order to provide a basis for speculation about how the study of exosomes may affect the fields of nephrology and renal physiology in the next few years.

Imatinib ameliorates renal morphological changes in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension

The present study was performed to assess the effects of the platelet-derived growth factor (PDGF) receptor kinase inhibitor imatinib mesylate on the renal morphological changes occurring during the development of malignant hypertension in transgenic rats with inducible expression of the Ren2 gene [TGR(Cyp1a1Ren2)]. Arterial blood pressure was measured by radiotelemetry in male Cyp1a1-Ren2 rats during control conditions and during dietary administration of indole-3-carbinol (I3C; 0.3%) for 14 days to induce malignant hypertension. Rats induced with I3C (n = 5) had higher mean arterial pressures (178 ± 4 vs. 109 ± 2 mmHg, P < 0.001) and increased urinary albumin excretion (Ualb; 13 ± 5 vs. 0.6 ± 0.2 mg/day) compared with noninduced rats (n = 5). Chronic administration of imatinib (60 mg·kg(-1)·day(-1) in drinking water, n = 5) did not alter the magnitude of the hypertension (176 ± 8 mmHg) but prevented the increase in Ualb (1.6 ± 0.3 mg/day). Quantitative analysis of proliferating cell nuclear antigen using immunohistochemistry demonstrated increased proliferating cell number in cortical tubules (38 ± 5 vs. 18 ± 1 cells/mm(2)) and cortical interstitium (40 ± 7 vs. 13 ± 6 cells/mm(2)) of hypertensive rat kidneys. Renal cortical fibrosis evaluated by picrosirius red staining showed increased collagen deposition in kidneys of the hypertensive rats (1.6 ± 0.1 vs. 0.4 ± 0.1% of cortical area). Imatinib attenuated the increase in proliferating cell number in cortical tubules and interstitium (22 ± 5 vs. 38 ± 5 and 22 ± 6 vs. 40 ± 7 cells/mm(2), respectively) and reduced the degree of collagen deposition (0.8 ± 0.2 vs. 1.6 ± 0.1%) in the kidneys of hypertensive rats. These findings demonstrate that the renal pathological changes that occur during the development of malignant hypertension in Cyp1a1-Ren2 rats involve activation of PDGF receptor kinase.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.

Increased renin excretion is associated with augmented urinary angiotensin II levels in chronic angiotensin II-infused hypertensive rats

Renin expression in principal cells of collecting ducts (CD) is upregulated in angiotensin II (ANG II)-dependent hypertensive rats; however, it remains unclear whether increased CD-derived renin undergoes tubular secretion. Accordingly, urinary levels of renin (uRen), angiotensinogen (uAGT), and ANG II (uANG II) were measured in chronic ANG II-infused Sprague-Dawley rats (80 ng/min for 14 days, n = 10) and sham-operated rats (n = 10). Systolic blood pressure increased in the ANG II rats by day 5 and continued to increase throughout the study (day 13; ANG II: 175 ± 10 vs. sham: 116 ± 2 mmHg; P < 0.05). ANG II infusion increased renal cortical and medullary ANG II levels (cortical ANG II: 606 ± 72 vs. 247 ± 43 fmol/g; P < 0.05; medullary ANG II: 2,066 ± 116 vs. 646 ± 36 fmol/g; P < 0.05). Although plasma renin activity (PRA) was suppressed in the ANG II-infused rats (0.3 ± 0.2 vs. 5.5 ± 1.8 ng ANG I·ml(-1)·h(-1); P < 0.05), renin content in renal medulla was increased (12,605 ± 1,343 vs. 7,956 ± 765 ng ANG I·h(-1)·mg(-1); P < 0.05). Excretion of uAGT and uANG II increased in the ANG II rats [uAGT: 1,107 ± 106 vs. 60 ± 26 ng/day; P < 0.0001; uANG II: 3,813 ± 431 vs. 2,080 ± 361 fmol/day; P < 0.05]. By day 13, despite suppression of PRA, urinary prorenin content increased in ANG II rats [15.7 ± 3 vs. 2.6 ± 1 × 10(-3) enzyme units excreted (EUE)/day, P < 0.01] as was the excretion rate of renin (8.6 ± 2 × 10(-6) EUE/day) compared with sham (2.8 ± 1 × 10(-6) EUE/day; P < 0.05). Urinary renin and prorenin protein levels examined by Western blot were augmented ∼10-fold in the ANG II-infused rats. Concomitant AT(1) receptor blockade with candesartan prevented the increase. Thus, in ANG II-dependent hypertensive rats with marked PRA suppression, increased urinary levels of renin and prorenin reflect their augmented secretion by CD cells into the luminal fluid. The greater availability of renin and AGT in the urine reflects the capability for intratubular ANG II formation which stimulates sodium reabsorption in distal nephron segments.

Urinary angiotensinogen as a biomarker of nephropathy in childhood

While most circulating angiotensinogen (AGT) is synthesized in the liver, the kidneys also produce AGT. Recently, we reported that urinary AGT is mainly originated from AGT. Using newly developed human AGT ELISA, we measured urinary AGT levels in chronic glomerulonephritis (GN) patients and patients with type 1 diabetes in childhood. Urinary AGT level was positively correlated with diastolic blood pressure, urinary albumin, urinary protein levels, and urinary occult blood in chronic GN patients. Furthermore, urinary AGT level was significantly increased in chronic GN patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects. Importantly, patients treated with RAS blockers had a marked attenuation of this increase. Also, urinary AGT level was significantly higher in patients with diabetic nephropathy in the premicroalbuminuric phase than in control subjects. These results suggest that urinary AGT reflects intrarenal RAS status in chronic GN and may be an early marker of diabetic nephropathy.

Urinary angiotensinogen as a predictive marker in patients with immunoglobulin A nephropathy

BACKGROUND

The intrarenal renin-angiotensinogen system (RAS) plays a major role in the progression of chronic kidney disease. Urinary angiotensinogen (UAGT) provides a specific index of the intrarenal RAS status. This study was conducted to find the role of UAGT as a predictive marker in patients with immunoglobulin A nephropathy (IgAN).

METHODS

Thirty-six patients with IgAN, 14 non-IgAN and 15 healthy controls were included. The UAGT concentration was measured using human ELISA kits and adjusted by urinary creatinine.

RESULTS

UAGT levels were significantly higher in patients with IgAN and non-IgAN than in healthy subjects (104.96 vs. 6.71 ng/mgCr, p < 0.01). Using univariate regression analysis, UAGT was found to correlate with the urine protein-to-creatinine ratio (UPCR), serum creatinine, and systolic and diastolic blood pressure in patients with IgAN. Multivariate regression analysis revealed that UAGT correlated positively with UPCR. Patients with levels of UAGT >100 ng/mgCr showed higher serum creatinine after treatment than patients with UAGT levels <100 ng/mgCr.

CONCLUSION

This study showed that UAGT levels are increased and correlate positively with the UPCR in IgAN. Patients with high levels of UAGT may have poor renal function following treatment.

Overview of endocrine systems in primary hypertension

Multiple hormonal factors play a major role in the functional and structural abnormalities of hypertension (HT). At present, the kidneys and, in particular, renal Na(+) retention are thought to constitute a primary and sustaining mechanism in the development of HT. However, the precise renal and hormonal mechanisms leading to increased Na(+) reabsorption and HT remain unknown. Because the vast majority of HT is primary, this article focuses on the major endocrine systems, the RAS, aldosterone, and the SNS, that play a prominent role in the pathogenesis of HT.

AT1A angiotensin receptors in the renal proximal tubule regulate blood pressure

Hypertension affects more than 1.5 billion people worldwide but the precise cause of elevated blood pressure (BP) cannot be determined in most affected individuals. Nonetheless, blockade of the renin-angiotensin system (RAS) lowers BP in the majority of patients with hypertension. Despite its apparent role in hypertension pathogenesis, the key cellular targets of the RAS that control BP have not been clearly identified. Here we demonstrate that RAS actions in the epithelium of the proximal tubule have a critical and nonredundant role in determining the level of BP. Abrogation of AT(1) angiotensin receptor signaling in the proximal tubule alone is sufficient to lower BP, despite intact vascular responses. Elimination of this pathway reduces proximal fluid reabsorption and alters expression of key sodium transporters, modifying pressure-natriuresis and providing substantial protection against hypertension. Thus, effectively targeting epithelial functions of the proximal tubule of the kidney should be a useful therapeutic strategy in hypertension.

Intrarenal angiotensin-converting enzyme induces hypertension in response to angiotensin I infusion

The contribution of the intrarenal renin-angiotensin system to the development of hypertension is incompletely understood. Here, we used targeted homologous recombination to generate mice that express angiotensin-converting enzyme (ACE) in the kidney tubules but not in other tissues. Mice homozygous for this genetic modification (ACE 9/9 mice) had low BP levels, impaired ability to concentrate urine, and variable medullary thinning. In accord with the ACE distribution, these mice also had reduced circulating angiotensin II and high plasma renin concentration but maintained normal kidney angiotensin II levels. In response to chronic angiotensin I infusions, ACE 9/9 mice displayed increased kidney angiotensin II, enhanced rate of urinary angiotensin II excretion, and development of hypertension. These findings suggest that intrarenal ACE-derived angiotensin II formation, even in the absence of systemic ACE, increases kidney angiotensin II levels and promotes the development of hypertension.

Intrarenal angiotensin II and its contribution to the genesis of chronic hypertension

The increased activity of intrarenal renin-angiotensin system (RAS) in a setting of elevated arterial pressure elicits renal vasoconstriction, increased sodium reabsorption, proliferation, fibrosis and renal injury. Increases in intrarenal and interstitial angiotensin (Ang) II levels are due to increased AT(1) receptor mediated Ang II uptake and stimulation of renal angiotensinogen (AGT) mRNA and protein expression. Augmented proximal tubule AGT production increases tubular AGT secretion and spillover of AGT into the distal nephron and urine. Increased renin formation by principal cells of the collecting ducts forms Ang I from AGT thus increasing Ang II. The catalytic actions of renin and prorenin are enhanced by prorenin receptors (PRRs) on the intercalated cells. The resultant increased intrarenal Ang II levels contribute to the genesis of chronic hypertension.

Adenosine sensitization after angiotensin II stimulation in afferent arterioles from normal rats does not occur during two-kidney, one-clip hypertension

AIMS

G protein-coupled receptors such as the AT(1a) R are frequently subject to desensitization, extensively studied in cell culture but to small extent in hypertensive models. Recently, angiotensin II (ANG II)-induced desensitization was shown to last 10 min in isolated afferent arterioles (AAs), suggesting impact on ANG II vasoactivity. In the present study, we explored ANG II desensitization and effects of adenosine (Ado) in AAs from two-kidney, one-clip (2K1C) hypertensive rats. Our main hypothesis was that Ado affects ANG II contractility differently in 2K1C, because of persistently elevated levels of ANG II.

METHODS

Afferent arterioles were isolated with the agarose-infusion/enzyme-treatment technique from normotensive and 2K1C hypertensive rats, and stimulated with ANG II (10(-7) M) at baseline and re-stimulated after 20 or 40 min, with or without Ado (2.5 × 10(-5) M) in the vessel bath.

RESULTS

Afferent arterioles from normotensive rats re-stimulated with ANG II after 20 min displayed a blunted contraction (Δ12.8 ± 4.3%, P < 0.05), which disappeared when AAs were stimulated after 40 min (Δ2.7 ± 2.3%, NS), indicating that desensitization lasted for 30 ± 10 min. Ado augmented ANG II contractions after 20 min, but not after 40 min, suggesting that only de-sensitized vessels were affected. Similar experiments in AAs from the clipped and non-clipped kidneys revealed no desensitization when re-stimulated with ANG II after 20 and 40 min, and contractions were unaffected by Ado.

CONCLUSIONS

Reduced duration of desensitization in AAs from 2K1C may cause vessels to be sensitized longer and increase vasoconstriction. The present study demonstrates that Ado does not augment ANG II-induced contractions in AAs from 2K1C as in normotensive rats, possibly because of a reduced period of desensitization.

Angiotensinogen Expression Is Enhanced in the Progression of Glomerular Disease

Intrarenal renin-angiotensin system (RAS) activation plays a critical role in the development and progression of renal injury. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by multiple independent mechanisms. Angiotensinogen (AGT) is the only known substrate for renin that is a rate-limiting enzyme of the RAS. Recently, enhanced intrarenal AGT levels have been shown to reflect the intrarenal RAS status in hypertension, chronic glomerular disease and diabetic nephropathy. In this review, we focus on AGT expression of the diseased glomeruli in the progression of glomerular disease. An anti-glomerular basement membrane nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of AGT and Ang II. The addition of Ang II type 1 receptor blocker to CC-chemokine recaptor 2 antagonist markedly attenuated the induction of macrophage infiltration, AGT and Ang II, and reduced glomerular crescent formation. Next, the levels of glomerular AGT expression and marker of reactive oxygen species in Zucker diabetic fatty (ZDF) obese rats were higher than those in ZDF lean rats. Hydrogen peroxide (H(2)O(2)) induced an increase in the AGT expression in primary rat mesangial cells. Furthermore, the H(2)O(2)-induced upregulation of AGT was inhibited by a mitogen-activated protein kinase kinase and a c-Jun N-terminal kinase inhibitor. These data suggest the potential contribution of enhanced AGT expression in glomeruli to the intrarenal RAS activation for the development of glomerular disease.

Urinary Angiotensinogen as a Novel Biomarker of Intrarenal Renin-Angiotensin System in Chronic Kidney Disease

An activated intrarenal reninangiotensin system (RAS) plays a crucial role in the pathogenesis of hypertension and chronic kidney diseases (CKD). Angiotensinogen (AGT) is the only known substrate for renin, which is the rate-limiting enzyme of the RAS. Because the levels of AGT are close to the Michaelis-Menten constant for renin, AGT levels can also control the RAS activity, and upregulation of AGT may lead to elevated angiotensin peptide levels and increases in blood pressure. Recent studies on experimental animal models have documented the involvement of AGT in the intrarenal RAS activation and development of hypertension. Enhanced intrarenal AGT mRNA and/or protein levels occur in experimental models of hypertension and kidney diseases supporting important roles in the development and progression of hypertension and kidney diseases. Urinary excretion rates of AGT provide a specific index of intrarenal RAS status in angiotensin II-infused rats. Also, a direct quantitative method was recently developed to measure urinary AGT using human AGT ELISA. These data prompted us to measure urinary AGT in patients with hypertension and CKD, and investigate correlations with clinical parameters. This brief review will address the potential of urinary AGT as a novel biomarker of the intrarenal RAS status in hypertension and CKD.

Intrarenal renin angiotensin system revisited: role of megalin-dependent endocytosis along the proximal nephron

The existence of a local renin angiotensin system (RAS) of the kidney has been established. Angiotensinogen (AGT), renin, angiotensin-converting enzyme (ACE), angiotensin receptors, and high concentrations of luminal angiotensin II have been found in the proximal tubule. Although functional data have documented the relevance of a local RAS, the dualism between biosynthesis and endocytotic uptake of its components and their cellular processing has been incompletely understood. To resolve this, we have selectively analyzed their distribution, endocytosis, transcytosis, and biosynthesis in the proximal tubule. The presence of immunoreactive AGT, restricted to the early proximal tubule, was due to its retrieval from the ultrafiltrate and storage in endosomal and lysosomal compartments. Cellular uptake was demonstrated by autoradiography of radiolabeled AGT and depended on intact endocytosis. AGT was identified as a ligand of the multiple ligand-binding repeats of megalin. AGT biosynthesis was restricted to the proximal straight tubule, revealing substantial AGT mRNA expression. Transgenic AGT overexpression under the control of an endogenous promoter was also restricted to the late proximal tubule. Proximal handling of renin largely followed the patterns of AGT, whereas its local biosynthesis was not significant. Transcytotic transport of AGT in a proximal cell line revealed a 5% recovery rate after 1 h. ACE was expressed along late proximal brush-border membrane, whereas ACE2 was present along the entire segment. Surface expression of ACE and ACE2 differed as a function of endocytosis. Our data on the localization and cellular processing of RAS components provide new aspects of the functional concept of a "self-contained" renal RAS.

Urinary angiotensinogen is correlated with blood pressure in men (Bogalusa Heart Study)

BACKGROUND

The Bogalusa Heart Study is a long-term study on cardiovascular disease and has followed a biracial (black/white) population from childhood. Risk factor data pertaining to many patients have been collected over 35 years, and the time course of hypertension has been documented by repeated examinations and measurements. Considerable sex and racial differences have been found to be related to cardiovascular disease. Urinary angiotensinogen (UAGT) is a novel biomarker for the intrarenal activity of the renin-angiotensin system in hypertension and kidney disease. We aimed to determine the relationship of UAGT with traditional cardiovascular disease risk factors in asymptomatic young adults in this biracial population.

METHOD

We recruited 251 individuals and collected a single random spot urine sample from each one. Because UAGT is significantly increased in diabetic patients and the use of antihypertensive drugs affects UAGT levels, we excluded patients who had diabetes, who were receiving antihypertensive treatment, or both. Consequently, 190 participants were included for this analysis.

RESULTS

UAGT levels did not differ with race or sex, but were significantly correlated with SBP (r = +0.23, P = 0.0015) and DBP (r = +0.24, P = 0.0012). Moreover, high correlations were shown in men, especially in black men (SBP, r = +0.85, P = 0.0005 and DBP, r = +0.72, P = 0.0079). Thus, UAGT is correlated with blood pressure in men, even when they do not show overt proteinuria or albuminuria.

CONCLUSION

The biomarker, UAGT, may facilitate the identification of individuals that are at increased risk for the development of hypertension and early asymptomatic renal disease.

The renin-angiotensin system and hypertension in autosomal recessive polycystic kidney disease

Hypertension is a well-recognized complication of autosomal recessive polycystic kidney disease (ARPKD). The renin-angiotensin system (RAS) is a key regulator of blood pressure; however, data on the RAS in ARPKD are limited and conflicting, showing both up- and down-regulation. In the current study, we characterized intrarenal and systemic RAS activation in relationship to hypertension and progressive cystic kidney disease in the ARPKD orthologous polycystic kidney (PCK) rat. Clinical and histological measures of kidney disease, kidney RAS gene expression by quantitative real-time PCR, angiotensin II (Ang II) immunohistochemistry, and systemic Ang I and II levels were assessed in 2-, 4-, and 6-month-old cystic PCK and age-matched normal rats. PCK rats developed hypertension and progressive cystic kidney disease without significant worsening of renal function or relative kidney size. Intrarenal renin, ACE and Ang II expression was increased significantly in cystic kidneys; angiotensinogen and Ang II Type I receptor were unchanged. Systemic Ang I and II levels did not differ. This study demonstrates that intrarenal, but not systemic, RAS activation is a prominent feature of ARPKD. These findings help reconcile previous conflicting reports and suggest that intrarenal renin and ACE gene upregulation may represent a novel mechanism for hypertension development or exacerbation in ARPKD.

Resveratrol improves cardiovascular function and reduces oxidative organ damage in the renal, cardiovascular and cerebral tissues of two-kidney, one-clip hypertensive rats

OBJECTIVES

The putative protective effects of resveratrol against oxidative injury in the heart, kidney and brain tissues of rats induced with the two-kidney, one-clip (2K1C) hypertension model were investigated.

METHODS

Wistar albino rats were divided into sham-operated (n = 8) or 2K1C groups, in which rats received either resveratrol (10 mg/kg per day, i.p., n = 8), or saline (n = 8) starting at Week 3 after the surgery and continuing for the following 6 weeks. Indirect blood pressure recordings and echocardiographic images were made to evaluate cardiac function. At the end of Week 9 the animals were decapitated and plasma, heart, kidney and brain were taken for biochemical assays, while aortic rings were prepared for vascular reactivity studies.

KEY FINDINGS

2K1C hypertension resulted in increased blood pressure, aortic hypercontractility and reduced left ventricular function, leading to increased lipid peroxidation and myeloperoxidase activity, concomitant with significant reductions in tissue glutathione, superoxide dismutase, Na+/K+-ATPase and catalase activities in the cardiac, renal and brain tissues, indicating the presence of oxidative tissue damage in peripheral target organs. Elevated plasma levels of lactate dehydrogenase, creatine kinase, as well as reduced plasma levels of antioxidant capacity and nitric oxide further verified the severity of oxidative injury. A 6-week treatment with resveratrol reversed all the measured parameters, ameliorated hypertension-induced oxidative injury in the target organs and improved cardiovascular function.

CONCLUSIONS

Resveratrol improved cardiovascular function through the augmentation of endogenous antioxidants and the inhibition of lipid peroxidation by maintaining a balance in oxidant/antioxidant status, which also ameliorated hypertension-induced oxidative injury in the cardiac, renal and cerebral tissues.

Renal vascular response to angiotensin II inhibition in intensive antihypertensive treatment of essential hypertension

INTRODUCTION

High blood pressure (BP) leads to target organ damage. It is suggested that regression of early organ lesions is possible on condition of BP normalization. The study objective was to assess whether permanent reduction of BP to the recommended values modifies renal vascular response to acute angiotensin II inhibition in the Doppler captopril test (DCT) in patients with essential hypertension (EH).

MATERIAL AND METHODS

Twenty-nine persons (58 kidneys) were found eligible for the study: 18 patients with EH and 11 healthy volunteers constituting the control group. Glomerular filtration rate estimation (eGFR), 24-h ambulatory BP monitoring (ABPM) and DCT with evaluation of renal resistive index change (ΔRI) were performed before and after a 6-month period of intensive antihypertensive therapy (IAT). Additional ABPM was performed at the end of IAT.

RESULTS

The mean IAT period was 8.5 ±2.4 months. The mean 24-h values of systolic and diastolic BP in the EH group were significantly lower in the IAT period than at the beginning and at the end of the study. Significantly lower systolic and diastolic BP (p < 0.05) and improvement of renal function (eGFR 121 ±38 vs. 139 ±40 ml/min, p < 0.001) were found after IAT as compared to initial values. Before IAT, ΔRI was significantly lower in the EH group as compared to the controls, but no such differences were found after IAT.

CONCLUSIONS

In EH patients, intensive BP lowering to the recommended values was associated with improvement of renal function and normalisation of renal vascular response to acute angiotensin II inhibition.

Intrarenal suppression of angiotensin II type 1 receptor binding molecule in angiotensin II-infused mice

ATRAP [ANG II type 1 receptor (AT1R)-associated protein] is a molecule which directly interacts with AT1R and inhibits AT1R signaling. The aim of this study was to examine the effects of continuous ANG II infusion on the intrarenal expression and distribution of ATRAP and to determine the role of AT1R signaling in mediating these effects. C57BL/6 male mice were subjected to vehicle or ANG II infusions at doses of 200, 1,000, or 2,500 ng·kg(-1)·min(-1) for 14 days. ANG II infusion caused significant suppression of ATRAP expression in the kidney but did not affect ATRAP expression in the testis or liver. Although only the highest ANG II dose (2,500 ng·kg(-1)·min(-1)) provoked renal pathological responses, such as an increase in the mRNA expression of angiotensinogen and the α-subunit of the epithelial sodium channel, ANG II-induced decreases in ATRAP were observed even at the lowest dose (200 ng·kg(-1)·min(-1)), particularly in the outer medulla of the kidney, based on immunohistochemical staining and Western blot analysis. The decrease in renal ATRAP expression by ANG II infusion was prevented by treatment with the AT1R-specific blocker olmesartan. In addition, the ANG II-mediated decrease in renal ATRAP expression through AT1R signaling occurred without an ANG II-induced decrease in plasma membrane AT1R expression in the kidney. On the other hand, a transgenic model increase in renal ATRAP expression beyond baseline was accompanied by a constitutive reduction of renal plasma membrane AT1R expression and by the promotion of renal AT1R internalization as well as the decreased induction of angiotensinogen gene expression in response to ANG II. These results suggest that the plasma membrane AT1R level in the kidney is modulated by intrarenal ATRAP expression under physiological and pathophysiological conditions in vivo.

Angiotensin II enhances connecting tubule glomerular feedback

Increasing Na delivery to epithelial Na channels (ENaCs) in the connecting tubule (CNT) causes dilation of the afferent arteriole (Af-Art), a process we call CNT glomerular feedback (CTGF). Angiotensin II (Ang II) stimulates ENaC in the collecting duct via Ang II type 1 receptors. We hypothesized that Ang II in the CNT lumen enhances CTGF by activation of Ang II type 1 receptors, protein kinase C and ENaC. Rabbit afferent arterioles and their adherent CNT were microperfused and preconstricted with norepinephrine. Each experiment involved generating 2 consecutive concentration-response curves by increasing NaCl in the CNT lumen. During the control period, the maximum dilation of the afferent arteriole was 7.9±0.4 μm, and the concentration of NaCl in the CNT needed to achieve half maximal response (EC(50)) was 34.7±5.2 mmol/L. After adding Ang II (10(-9) mol/L) to the CNT lumen, the maximal response was 9.5±0.7 μm and the EC(50) was 11.6±1.3 mmol/L (P=0.01 versus control). Losartan, an Ang II type 1 antagonist (10(-6) mol/L) blocked the stimulatory effect of Ang II; PD123319, an Ang II type 2 antagonist (10(-6) mol/L), did not. The protein kinase C inhibitor staurosporine (10(-8) mol/L) added to the CNT inhibited the stimulatory effect of Ang II. The ENaC inhibitor benzamil (10(-6) mol/L) prevented both CTGF and its stimulation by Ang II. We concluded that Ang II in the CNT lumen enhances CTGF via activation of Ang II type 1 and that this effect requires activation of protein kinase C and ENaC. Potentiation of CTGF by Ang II could help preserve glomerular filtration rate in the presence of renal vasoconstriction.