Angiotensin type 1 receptor antagonism and ACE inhibition produce similar renoprotection in N(omega)-nitro-L>-arginine methyl ester/spontaneously hypertensive rats

Azilsartan causes natriuresis due to its sympatholytic action in kidney disease

The sympathoinhibitory mechanism of azilsartan was investigated in an adenine-induced chronic renal failure model. Azilsartan exerted an antihypertensive effect, though BP elevation induced by adenine was marginal. The creatinine value was significantly lower in the azilsartan group (AZ) than in the vehicle group (VEH); furthermore, proteinuria was suppressed, and sodium excretion was augmented in the AZ group. The low frequency (LF) of systolic BP was suppressed (VEH: 4.07 ± 2.67 mmHg² vs. AZ: 3.32 ± 1.93 mmHg² P < 0.001), and the spontaneous baroreflex gain (sBRG) was augmented (VEH: 1.04 ± 0.62ms/mmHg vs. AZ: 1.38 ± 0.69 ms/mmHg, P < 0.001) in AZ. There were no significant differences in ACE1 and ACE2 expression between the groups, which indicated that the action of azilsartan on these components of the intrarenal renin-angiotensin-aldosterone system was comparatively small. Although NHE3, NKCC, and ENaC expression was similar between the groups, NaCl cotransporter (NCC) expression was markedly suppressed by azilsartan (P < 0.05). Thus, in a mild chronic kidney disease (CKD) model with slight BP elevation, the sympatholytic effect of ARB might be expected, and azilsartan might exert its natriuretic effect by NCC suppression achieved by sympathoinhibitory activity.

Aliskiren and valsartan in combination is a promising therapy for hypertensive renal injury in rats

Neither ACEI nor ARBs completely repress the RAAS. Aliskiren is a newer agent that inhibits renin. However, it increases the biosynthesis and secretion of renin and prorenin, that might induce renal tissue damage. This study was conducted to investigate the renoprotective effects of aliskiren and valsartan the ARB, either alone or in combination, on hypertensive nephropathy induced by L-NAME. Aliskiren (50 mg/kg/daily i.p.), valsartan (10 mg/kg daily i.p.) alone or in half dose combination were administered with L-NAME (30-40 mg daily in drinking water) for 8 weeks. Aliskiren and valsartan significantly reduced systolic blood pressure, proteinuria, serum creatinine, blood urea nitrogen, oxidative stress, and structural renal injury although not to the same extent. Valsartan reduced systolic blood pressure and proteinuria in L-NAME treated rats more significantly than aliskiren. However, glomerular collapse index and the expansion of interstitial tissue were significantly attenuated by aliskiren than by valsartan. Cotreatment with aliskiren and valsartan markedly reduced the oxidative stress and further reduced the glomerular collapse and the expansion of interstitial tissue compared with aliskiren monotherapy.

CONCLUSION

These results suggest that therapies aimed at different targets within the RAAS may have additional effects in attenuating structural injury in experimental hypertensive nephropathy.

Angiotensin II or epinephrine hemodynamic and metabolic responses in the liver of L-NAME induced hypertension and spontaneous hypertensive rats

AIM

To study hepatic vasoconstriction and glucose release induced by angiotensin (Ang)II or Epi in rats with pharmacological hypertension and spontaneously hypertensive rat (SHR).

METHODS

Isolated liver perfusion was performed following portal vein and vena cava cannulation; AngII or epinephrine (Epi) was injected in bolus and portal pressure monitored; glucose release was measured in perfusate aliquots.

RESULTS

The portal hypertensive response (PHR) and the glucose release induced by AngII of L-NAME were similar to normal rats (WIS). On the other hand, the PHR induced by Epi in L-NAME was higher whereas the glucose release was lower compared to WIS. Despite the similar glycogen content, glucose release induced by AngII was lower in SHR compared to Wistar-Kyoto rats although both PHR and glucose release induced by Epi in were similar.

CONCLUSION

AngII and Epi responses are altered in different ways in these hypertension models. Our results suggest that inhibition of NO production seems to be involved in the hepatic effects induced by Epi but not by AngII; the diminished glucose release induced by AngII in SHR is not related to glycogen content.

Hyperuricemia: A Biomarker of Renal Hemodynamic Impairment

BACKGROUND

Many epidemiological, clinical, and experimental reports have demonstrated an association between serum uric acid concentration and a variety of cardiovascular and renal diseases, particularly in hypertension. At present, there seems to be no resolution to the question whether this relationship is causal or coincidental.

SUMMARY

This discussion examines a number of biological, pathophysiological, fundamental, and clinical relationships between serum uric acid concentration and several of these disorders. To this end, discussion and review provide some specific insight conclusions and recommendations related to their clinical relevance.

KEY MESSAGES

We suggest that, in most instances (especially in patients with essential hypertension), the increase in serum uric acid concentration is coincidental, serving as a useful biomarker that relates the magnitude of circulating plasma uric acid concentration with the extent of impaired cardiovascular and renal function. Moreover, the value of certain pharmaceutical agents affecting the serum uric acid level should be considered carefully by taking into consideration the associated pathophysiological derangements.

Renal antifibrotic effect of N-acetyl-seryl-aspartyl-lysyl-proline in diabetic rats

BACKGROUND AND AIM

Diabetic nephropathy is the main cause of end-stage renal disease. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), a physiological tetrapeptide hydrolyzed by the angiotensin-converting enzyme (ACE), has antifibrotic effects in the cardiovascular system and in the kidney in experimental models of hypertension, heart failure and renal disease. The aim of the study was to evaluate the effect of Ac-SDKP in diabetic nephropathy and the potential additive effect of Ac-SDKP, when compared to ACE inhibitors alone, on the development of renal fibrosis.

METHOD

Diabetes was induced in 28 Sprague-Dawley rats by a single intraperitoneal injection of streptozotocin. Control rats (n = 10) received only buffer solution. An ACE inhibitor (ramipril, 3 mg/kg/day) was administered to 11 diabetic rats. After 2 months, Ac-SDKP (1 mg/kg/day) was administered by osmotic minipumps for 8 weeks to 7 diabetic rats and to 6 diabetic rats treated with ramipril. Osmotic minipumps delivered saline solution in the corresponding sham-treated rats (diabetic rats, n = 10, and ramipril-treated diabetic rats, n = 5).

RESULTS

Diabetic rats showed a significant increase in blood glucose level, urinary albumin excretion and renal fibrosis, and a reduction of glomerular nephrin expression with respect to control rats. Ac-SDKP administration significantly reduced renal fibrosis in diabetic rats, without significantly reducing urinary albumin excretion. Ramipril treatment caused a significant decrease in albuminuria and renal fibrosis and restored glomerular nephrin expression. Administration of Ac-SDKP, in addition to ramipril, further reduced renal fibrosis with respect to ramipril alone, while it did not improve the antiproteinuric effect of ramipril.

CONCLUSION

Ac-SDKP administration reduces renal fibrosis in diabetic nephropathy. Addition of Ac-SDKP to ACE inhibition therapy improves the reduction of renal fibrosis with respect to ACE inhibition alone, suggesting a beneficial effect of this pharmacological association in diabetic nephropathy.

Angiopoietin-1 gene therapy attenuates hypertension and target organ damage in nitric oxide synthase inhibited spontaneously hypertensive rats

Background and Objectives

In our previous study, we found that the gene transfer of a potent derivative of cartilage oligomeric matrix protein Angiopoietin-1 (COMP-Ang-1) substantially prevented hypertension, microvascular rarefaction, and target organ damage in spontaneously hypertensive rats (SHRs). The purpose of the present study was to examine the role of nitric oxide (NO) in the therapeutic effects observed after COMP-Ang-1 gene transfer.

Materials and Methods

To exclude the NO-mediated effects in COMP-Ang-1 gene therapy, the SHRs were treated with an NO synthase (NOS) inhibitor, N^w-nitro-L-arginine methyl ester (L-NAME) before the electrophoretic gene transfer.

Results

The pretreatment with L-NAME induced a severe and sustained increase in systolic blood pressure (BP) in a LacZ plasmid transferred control SHR. However, the electrophoretic transfer of a COMP-Ang-1 plasmid instead of LacZ plasmid in L-NAME-pretreated SHRs substantially blocked the development of hypertension without any significant difference in comparison with L-NAME-untreated COMP-Ang-1 plasmid transferred groups. In addition, the COMP-Ang-1 plasmid transfer substantially attenuated microvascular rarefaction and arteriole remodeling in the heart and kidney, which might account for the mild histological alterations observed in the COMP-Ang-1 plasmid transferred group, in contrast to the severe fibrosis and necrosis seen in the LacZ plasmid controls.

Conclusion

These therapeutic outcomes of COMP-Ang-1 gene transfer even in NOS inhibited SHRs suggested that the antihypertensive effect of COMP-Ang-1 was not merely secondary to NO-mediated vasorelaxation, but it may be associated with its ability to protect the vascular endothelium probably via an NO-independent mechanism which serves to attenuate microvascular rarefaction and target organ damage, and also to prevent hypertension by reducing peripheral vascular resistance.

Salt-induced renal injury in spontaneously hypertensive rats: effects of nebivolol

BACKGROUND

we investigated renal effects of nebivolol, a selective β(1)-receptor blocker with additional antioxidative ability, in spontaneously hypertensive rats (SHR) where increased salt intake induces oxidative stress and worsens renal function as a result of further activation of the renin-angiotensin and sympathetic nervous systems.

METHODS

male SHR were given an 8% salt diet (HS; n = 22) for 5 weeks; their age-matched controls (n = 9) received standard chow. Nebivolol was given at a dose of 10 mg/kg/day for 5 weeks in 11 HS rats.

RESULTS

HS increased blood pressure, plasma renin concentration, urinary protein excretion, and renal nitroxidative stress while decreasing renal blood flow and angiotensin 1-7 receptor (mas) protein expression. There was no change in angiotensin II type 1 receptor expression among the experimental groups. Nebivolol did not alter the salt-induced increase in blood pressure but reduced urinary protein excretion, plasma renin concentration, and nitroxidative stress. Nebivolol also increased neuronal NOS expression while preventing the salt-induced decrease in renal blood flow and mas protein expression.

CONCLUSION

nebivolol prevented salt-induced kidney injury and associated proteinuria in SHR through a blood pressure-independent mechanism. Its protective effects may be related to reduction in oxidative stress, increases in neuronal NOS and restoration of angiotensin II type 1/mas receptor balance.

The diuretic effect in human subjects of an extract of Taraxacum officinale folium over a single day

BACKGROUND

Taraxacum officinale (L.) Weber (Asteraceae) has been extensively employed as a diuretic in traditional folk medicine and in modern phytotherapy in Europe, Asia, and the Americas without prior clinical trial substantiation.

OBJECTIVES

In this pilot study, a high-quality fresh leaf hydroethanolic extract of the medicinal plant T. officinale (dandelion) was ingested by volunteers to investigate whether an increased urinary frequency and volume would result.

DESIGN

Volume of urinary output and fluid intake were recorded by subjects. Baseline values for urinary frequency and excretion ratio (urination volume:fluid intake) were established 2 days prior to dandelion dosing (8 mL TID) and monitored throughout a 1-day dosing period and 24 hours postdosing.

RESULTS

For the entire population (n = 17) there was a significant (p < 0.05) increase in the frequency of urination in the 5-hour period after the first dose. There was also a significant (p < 0.001) increase in the excretion ratio in the 5-hour period after the second dose of extract. The third dose failed to change any of the measured parameters.

CONCLUSIONS

Based on these first human data, T. officinale ethanolic extract shows promise as a diuretic in humans. Further studies are needed to establish the value of this herb for induction of diuresis in human subjects.

Current challenges and unresolved problems in hypertensive disease

Over the past four or five decades, hypertension and cardiovascular medicine has experienced dramatic and innovative changes that have significantly reduced morbidity and mortality. A vast array of new antihypertensive compounds have been developed, which are able to inhibit many pathophysiologic mechanisms of the disease and prevent many of the outcomes in patients with hypertension. Much of this series of therapeutic breakthroughs have been the result of active participation of clinical scientists with tremendous and remarkable knowledge of and experience with the fundamental mechanisms of disease. In more recent years, much new information has appeared concerning the basis genetic and biologic mechanisms involved in cardiovascular and renal diseases. What remains of utmost importance is for members of the academic community with a wide spectrum of experience and points of view to continue to work with the fundamental problems and mechanisms of the diseases.

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.

Sex and sex hormones influence the development of albuminuria and renal macrophage infiltration in spontaneously hypertensive rats

There is a sex difference in hypertensive renal injury, with men experiencing greater severity and a more rapid progression of renal disease than women; however, the molecular mechanisms protecting against renal injury in women are unknown. The goal of this study was to determine whether sex hormones modulate blood pressure and the progression of albuminuria during the developmental phase of hypertension in male and female spontaneously hypertensive rats (SHR). Studies were also performed to examine how sex and sex hormones influence two major risk factors for albuminuria, overactivation of the renin-angiotensin system and oxidative stress. Blood pressure was measured by telemetry in gonad-intact and gonadectomized male and female SHR. Microalbumin excretion, measured over time, and macrophage infiltration were used to assess renal health. Male SHR had significantly higher blood pressures than female SHR, and gonadectomy decreased blood pressures in males with no effect in females. Male SHR displayed a gonad-sensitive increase in albuminuria over time, and female SHR had a gonad-sensitive suppression in macrophage infiltration. Female SHR had greater plasma ANG II levels and similar levels of renal cortical ANG II vs. levels shown in males but less AT(1)-receptor protein expression in the renal cortex. Female SHR also had a gonad-sensitive decrease in renal oxidative stress. Therefore, the renal protection afforded to female SHR is associated with lower blood pressure, decreased macrophage infiltration, and decreased levels of oxidative stress.

Is population-wide diuretic use directly associated with the incidence of end-stage renal disease in the United States?

In the quest for "evidence-based" medicine, an accepted hierarchy of evidence has been proposed. This hierarchy places in vitro studies and animal data at the base, and puts systematic reviews, meta-analyses, and randomized controlled trials at the pinnacle. However, when clinical medicine faces questions that have not yet been studied by the "gold standard" methods, how is one to proceed? Often, the best evidence at hand falls short of randomized controlled trials and meta-analyses. Using this framework, a review of the evidence supporting the hypothesis that population-wide diuretic use is directly associated with end-stage renal disease in the United States is presented. Publications pertaining to diuretic use in recent clinical trials are also discussed.

Young Scholars Award Lecture: Intratubular angiotensinogen in hypertension and kidney diseases

Recent findings related to the renin-angiotensin system have provided a more elaborated understanding of the pathophysiology of hypertension and kidney diseases. These findings have led to unique concepts and issues regarding the intrarenal renin-angiotensin system. Angiotensinogen is the only known substrate for renin that is the rate-limiting enzyme of the renin-angiotensin system. Because the level of angiotensinogen in human beings is close to the Michaelis-Menten constant value for renin, changes in angiotensinogen levels can control the activity of the renin-angiotensin system, and its upregulation may lead to elevated angiotensin peptide levels and increases in blood pressure. Enhanced intrarenal angiotensinogen mRNA or protein levels or both have been observed in multiple models of hypertension including angiotensin II-dependent hypertensive rats, Dahl salt-sensitive hypertensive rats, and spontaneously hypertensive rats, as well as in kidney diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, and radiation nephropathy. Renal angiotensinogen is formed primarily in proximal tubular cells and is secreted into the tubular fluid. Urinary angiotensinogen excretion rates show a clear relationship to kidney angiotensin II contents and kidney angiotensinogen levels, suggesting that urinary angiotensinogen may serve as an index of the intrarenal renin-angiotensin system status. Establishment of concise and accurate methods to measure human angiotensinogen may allow clinical studies that would provide important information regarding the roles of intrarenal angiotensinogen in the development and progression of hypertension and kidney diseases.

Uric acid: Its relationship to renal hemodynamics and the renal renin-angiotensin system

Reports relating hyperuricemia and hypertension have been filed for many decades. Nevertheless, controversy remains concerning serum uric acid concentration as an independent risk factor underlying coronary heart disease (CHD) and essential hypertension or as an indirect marker of renovascular involvement. Earlier studies in normotensive subjects and hypertensive patients demonstrated that serum uric acid concentration was closely related to intrarenal hemodynamic alterations, suggesting that it is an excellent marker of vascular involvement. Our data from clinical studies and in an animal model of severe hypertensive nephrosclerosis have strengthened this concept. Conversely, other reports have suggested that uric acid may be a pathogenetic factor. Supporting arguments for this theory maintain that experimental hyperuricemia induces hypertension and renal damage. Epidemiologically, hyperuricemia is associated with hypertension, CHD, renal disease, toxemia of pregnancy, and other outcomes, although mechanisms remain unclear. Additionally, there are no available data on the effects of lowering uric acid on pressure control and organ protection.

Early detection of progressive renal dysfunction in patients with coronary artery disease

BACKGROUND

An association between renal hemodynamic dysfunction and coronary artery disease (CAD) has been documented in chronic renal failure; however, no information is available in CAD patients with normal glomerular filtration rate (GFR). This study was aimed at evaluating early abnormalities and outcome of renal function in CAD patients.

METHODS

In 15 nondiabetic patients with normal renal function and no significant stenoses in renal arteries, and having undergone coronary arteriography, we studied systemic and renal hemodynamics before and after a vasodilating stimulus induced by aminoacid (AA) infusion. A control group (C) consisted of 15 sex- and age-matched kidney donors. The statistical adequacy of the sample size was preliminarily verified. Renal clearances were repeated after two years.

RESULTS

At baseline, GFR (mL/min/1.73 m2) averaged 81.4 +/- 3.8 in CAD and 83.7 +/- 1.4 in C (P= NS); RPF (mL/min/1.73 m2) was 297 +/- 22 in CAD and 456 +/- 15 in C (P < 0.0001); filtration fraction was higher in CAD (P < 0.001). Plasma renin activity was higher in CAD (P < 0.005). The number of coronary stenoses was inversely correlated with RPF but not with GFR. In CAD, at variance with C, AA did not induce any increment of GFR, while RPF increased without achieving the unstimulated value of C. Blood pressure was comparable in CAD and C at baseline and not modified by AA. After two years, a significant decrease in GFR (-14%, P < 0.001) and RPF (-15%, P < 0.001) occurred only in CAD, and in either group, the response to AA did not differ from that detected at baseline.

CONCLUSION

In CAD patients with normal GFR, reduction in renal perfusion and absence of renal functional reserve likely represent early markers of progressive renal dysfunction.

Physiologic evidence of renoprotection by antihypertensive therapy

PURPOSE OF REVIEW

Hypertension is vastly prevalent worldwide and constitutes the second leading cause of end-stage renal disease. Therefore, treating hypertension and protecting the kidney from deterioration are exceedingly important. Although previous studies have explored the renal effects of various antihypertensive drugs in animal models and humans, recent clinical trials are all the more convincing. This review summarizes the latest data demonstrating the physiologic evidence of renoprotection by antihypertensive therapy.

RECENT FINDINGS

Experimental studies in various models of hypertension with renal injury have demonstrated clearly that angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or aldosterone antagonists promote beneficial renal actions, through hemodynamic and nonhemodynamic mechanisms. Of particular significance, recent clinical trials have demonstrated renoprotection by angiotensin II inhibition in patients with hypertension and chronic kidney disease. Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade have provided equivalent renal benefits, and their dual action seems to confer greater renoprotection. The available data on the renal outcomes of other antihypertensive drugs such as calcium antagonists have been inconsistent.

SUMMARY

The results of the numerous experimental and clinical studies have established the renoprotective properties of renin-angiotensin-aldosterone inhibitors, which confer greater benefit by virtue of their effects over and beyond blood pressure reduction. These findings provide the convincing basis for the recommendation of angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or both as first-line therapy in hypertension with chronic kidney disease.

Superiority of combination of thiazide with angiotensin-converting enzyme inhibitor or AT1-receptor blocker over thiazide alone on renoprotection inl-NAME/SHR

The renal and glomerular dynamic effects of combining thiazide and angiotensin antagonists have not been reported. The present study was designed to examine the effects of hydrochlorothiazide (HCTZ) alone or in combination with an angiotensin-converting enzyme inhibitor or ANG II type 1-receptor blocker on renal hemodynamics, glomerular dynamics, renal function, and renal histopathology in the Nω-nitro-l-arginine methyl ester-treated spontaneously hypertensive rat (l-NAME/SHR) model. HCTZ (80 mg·kg−1·day−1) alone or in combination with enalapril (30 mg·kg−1·day−1) or losartan (30 mg·kg−1·day−1) or enalapril (15 mg·kg−1·day−1) plus losartan (15 mg·kg−1·day−1) was administered to l-NAME/SHR (5.0 ± 0.10 mg·kg−1·day−1) for 3 wk. Mean arterial pressure, total peripheral resistance, renal plasma flow, glomerular filtration rate, glomerular hydrostatic pressure, afferent and efferent glomerular arteriolar resistances, single nephron plasma flow, single nephron glomerular filtration rate, serum creatinine concentration, 24-h urinary protein excretion, and glomerular and arteriolar injury scores were determined. HCTZ reduced mean arterial pressure, total peripheral resistance, glomerular hydrostatic pressure, and afferent and efferent glomerular arteriolar resistances ( P < 0.05, at least) but slightly increased renal plasma flow and single nephron plasma flow associated with reduced serum creatinine concentration, urinary protein excretion, and arteriolar injury score compared with l-NAME/SHR control. However, the combination of enalapril and/or losartan with HCTZ markedly improved each of these functions. These results demonstrated minor benefits of HCTZ monotherapy and a marked superiority of its combination with enalapril and/or losartan over HCTZ monotherapy on renoprotection in l-NAME/SHR, thereby providing strong evidence of their clinical benefits for hypertensive patients with renal functional impairment.

Enhanced intrarenal angiotensinogen contributes to early renal injury in spontaneously hypertensive rats

This study was performed to determine whether augmented intrarenal angiotensinogen may contribute to the enhanced renal angiotensin II (Ang II) and associated tissue injury in spontaneously hypertensive rats (SHR). SHR and Wistar-Kyoto rats (WKY) were maintained on a normal diet and killed at either 7 or 14 wk of age. Two groups of SHR received either an Ang II type 1 receptor blocker (ARB; olmesartan, 5 mg/d) or a triple therapy (hydralazine 7.5 mg/d, reserpine 0.15 mg/d, and hydrochlorothiazide 3 mg/d [HRH]) during weeks 7 through 14. Systolic BP and renal Ang II were significantly increased in SHR-14 (n = 8) compared with WKY-7, WKY-14, and SHR-7 (n = 8 each), and ARB treatment prevented these increases (n = 8). However, whereas HRH treatment prevented the development of hypertension in SHR, this combination therapy failed to decrease renal Ang II (n = 8). With the use of urine samples or fixed renal sections, renal injuries in rats were quantified in a semiautomated manner by the following six parameters: (1) urinary excretion rate of total protein, (2) glomerular sclerosis, (3) interstitial expansion, (4) and (5) numbers of monocytes/macrophages in interstitium or glomeruli, and (6) arterial proliferation. Angiotensinogen mRNA and protein levels in kidney cortex, measured by real-time reverse transcriptase-PCR and Western blot analysis, respectively, and all six parameters of renal damage were changed in parallel, and ARB treatment also prevented these increases. However, HRH treatment failed to prevent these increases. These results indicate that SHR have enhanced intrarenal angiotensinogen production that contributes to increased Ang II levels leading to the development of hypertension and renal injury in this strain.

Effects of Losartan and Chlorthalidone on Blood Pressure and Renal Vascular Resistance Index in Non-Diabetic Patients with Essential Hypertension and Normal Renal Function

Antihypertensive drugs can differ in target organ protection despite similar blood pressure (BP) control. We compared the effects of losartan (L) and chlorthalidone (C) on renal vascular resistance index (RVRI) in 194 grade I to II, non-diabetic hypertensive patients with increased RVRI (>0.68 m/s by echo-Doppler) but normal renal function. Patients were randomly allocated to C 25 mg/d or L 50 mg/d according to a single blind, PROBE study design. After 4 weeks of treatment, 92 patients (48 L/44 C) with BP <140/90 mm Hg were enrolled in the long-term phase of the study. After 12 months a normalization of RVRI was observed in 47 of 48 patients treated with L (97.5%) and only in 14 of 44 of those treated with C (25.8%) despite no differences in BP control. Patients whose RVRI remained elevated during C therapy underwent a 2-week washout period and then were treated with L 50 mg/d for 12 additional months. After that period 28 of 30 (95%) of patients who were nonresponders to C showed a normalization of RVRI despite no differences in BP control. In conclusion, our data suggest that treatment with L can improve renal hemodynamic and exert a protective renal effect beyond BP control in patients with hypertension.

Imidapril improves l-NAME-exacerbated nephrosclerosis with TGF-β1 inhibition in spontaneously hypertensive rats

OBJECTIVE

This study was designed to investigate whether chronic angiotensin-converting enzyme (ACE) inhibition prevents hypertensive glomerular injury and inhibits increases in the mRNA levels and immunohistological expression of the apoptosis inducer caspase-3, and transforming growth factor (TGF)-beta 1 during prolonged nitric oxide synthase (NOS) inhibition with N-nitro-L-arginine methyl ester (L-NAME) in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

For 3 weeks, we studied three groups of 20-week-old male SHR: a control group, a l-NAME group, and a group treated with L-NAME and the ACE inhibitor imidapril. L-NAME rats developed severe hypertensive nephrosclerosis with significantly elevated blood pressure, markedly increased urinary protein excretion and serum creatinine levels, and more severe glomerulosclerosis and tubulo-interstitial changes. Levels of TGF-beta 1 mRNA in the renal tissue was also significantly increased in L-NAME rats compared with control SHR. Addition of imidapril significantly lowered blood pressure, inhibited nephrosclerosis and attenuated the mRNA level of TGF-beta 1 in comparison with L-NAME/SHR. Histologically, the glomerular cell apoptosis labeling index, terminal doxynucleotidil transferase-mediated dUTP nick-end labeling of fragmented DNA (TUNEL) and active caspase-3, and TGF-beta 1 positive areas were also reduced by imidapril.

CONCLUSION

These data suggest that imidapril prevents glomerular and arteriolar damages and renal functions, through inhibiting both TGF-beta 1 production and apoptosis induction.

Kidney adaptation in nitric oxide-deficient Wistar and spontaneously hypertensive rats

We investigated the renal structural and functional consequences of nitric oxide (NO) deficiency co-treated with angiotensin-converting enzyme inhibitor (ACEi) in 20 adult male Wistar rats and 20 spontaneously hypertensive rats (SHR). The animals were separated into eight groups (n = 5) and treated for 30 days: Control, L-NAME (NO deficient group), Enalapril, L-NAME + Enalapril. The elevated blood pressure in NO deficient rats was partially reduced by enalapril. Serum creatinine was elevated in L-NAME-SHRs and effectively treated with enalapril. The proteinuria was significantly higher only in L-NAME-SHRs, and this was reduced by treatment with ACEi. The glomerular volume density (Vv(gl)) in L-NAME rats, both Wistar and SHR, was greater than in matched control rats, and enalapril treatment effectively prevented this Vv(gl) increase. No significant differences were observed in tubular volume density, Vv(tub), or tubular surface density, Sv(tub), in all Wistar groups. The Vv(tub) was smaller in L-NAME-SHRs than in control SHRs, and this tubular alteration was not prevented by enalapril. The Sv(tub) was not different among the SHR groups. In Wistar rats no changes were seen in vascular surface density, but a greatly increased cortical vascular volume density was seen in the enalapril treated rats. The vascular length density was greatly diminished in NO deficient rats that was effectively prevented with enalapril treatment. The vascular cortical renal stereological indices are normally reduced in SHRs. Administration of enalapril, but not L-NAME, changed this tendency. However, enalapril was not totally effective in preventing vascular damage in SHR NO deficient animals.

Target organ involvement in hypertension: a realistic promise of prevention and reversal

The major message from this discussion is that the end points from hypertensive disease (stroke, CHD, and hypertensive emergencies) are now preventable. Cardiac failure and ESRD, however, two exceedingly common end points from long-standing hypertension, remain as major disabilities and causes of death. The former is the most common cause of hospitalization in industrialized societies; hypertension and diabetes mellitus are the most common causes of the latter. The mechanisms of risk of these target organ diseases is not LVH per se, or the elevated arterial pressure alone in the kidney, but the coronary and renal ischemia, organ fibrosis, and, perhaps, apoptosis. Present day therapy now can effectively reverse these costly (economically and by human suffering) complications. Recent experimental studies suggest that, when used early enough, these newer pharmacologic agents may even prevent their occurrences and consequences. The very practical lesson from these experiences is that early detection and treatment of hypertension, effective control of arterial pressure, and the suppression of the underlying disease mechanisms markedly reduce the now increasing prevalence of both cardiac and renal failure.

Combined effects of low-dose oral spironolactone and captopril therapy in a rat model of spontaneous hypertension and heart failure

The effects of low-dose oral spironolactone (SPIRO) in a rat model of hypertensive heart failure (spontaneously hypertensive heart failure rat) were compared with its effects when combined with captopril (CAP). Twenty-six spontaneously rats with hypertensive heart failure were treated with either placebo (CON), SPIRO (20 mg/kg/d by mouth), CAP (100 mg/kg/d by mouth), or both SPIRO and CAP for 12 weeks. This dose of oral SPIRO did not affect blood pressure, left ventricular end-diastolic diameter, left ventricular ejection fraction, plasma atrial natriuretic peptide concentration, or cardiac fibrosis; however, in combination with CAP, it exerted a significant depressor effect after 12 weeks of treatment that was accompanied by increased urine output and decreased urinary protein excretion. These effects were significantly greater than those with CAP treatment alone. A significant increase in plasma aldosterone level was observed only in CON (174 +/- 21%). These data suggest that the addition of low-dose SPIRO to angiotensin I-converting enzyme inhibitor treatment may prevent progression into end-stage congestive heart failure through synergistic effects on diuresis and renoprotection.

Omapatrilat induces profound renal vasodilation but does not affect coronary hemodynamics

BACKGROUND

Omapatrilat has potent enzymatic inhibitory effects on the angiotensin-converting enzyme and neutral endopeptidase. The prolonged effects of this inhibition on systemic and regional hemodynamics, cardiovascular mass, and hydroxyproline concentration in spontaneously hypertensive rats were studied. The contribution of endogenous bradykinin on the cardiovascular actions of omapatrilat in this genetic model of hypertension was also investigated.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular and aortic masses, and hydroxyproline concentration were determined in 35-week-old spontaneously hypertensive rats after 12 weeks of treatment with omapatrilat (40 mg/kg/day), with and without the bradykinin receptor antagonist icatibant (500 microg/kg/day). Omapatrilat decreased mean arterial pressure, reducing total peripheral resistance as well as decreased left ventricular and aortic mass indices. It also induced a profound renovasodilation associated with a decrease renal vascular resistance that markedly increased renal blood flow. Coronary hemodynamics and left ventricular hydroxyproline concentration remained unaltered. Concomitant blockade of bradykinin receptors partially attenuated the hypotensive effect of omapatrilat and its effect on aortic mass; and icatibant did not influence the renovasodilation.

CONCLUSION

Omapatrilat produced profoundly beneficial effects on systemic and renal hemodynamics, as well as on left ventricular and aortic masses, without any effect on coronary hemodynamics. These effects of omapatrilat on arterial pressure and aortic mass, but not on renal hemodynamics and left ventricular mass, may have been at least partially mediated through the action of bradykinin.

Cardiovascular status following combined angiotensin-converting enzyme and AT1 receptor inhibition in conscious spontaneously hypertensive rats

1. Combined treatment of spontaneously hypertensive rats (SHR) with AT1 receptor antagonists and angiotensin-converting enzyme (ACE) inhibitors has been shown to reduce mean arterial pressure (MAP) more than monotherapy with either agent. The aims of the present study were to investigate the effects of chronic dual renin-angiotensin system (RAS) inhibition using non-hypotensive doses of the AT1 receptor antagonist candesartan cilexetil and the ACE inhibitor perindopril on cardiovascular function and structure. 2. Adult male SHR, aged 15 weeks, were divided into four groups: (i) candesartan cilexetil (0.5 mg/kg per day in drinking water); (ii) perindopril (0.3 mg/kg per day in drinking water); (iii) combined treatment (dual RAS inhibition); or (iv) the appropriate vehicle (0.1% ethanol/0.1% polyethylene glycol/1.5 mmol/l sodium bicarbonate dissolved in water for candesartan cilexetil; distilled water for perindopril). Systolic blood pressure was measured weekly using the tail-cuff method and urinary microalbuminuria was measured fortnightly. 3. After 4 weeks, rats were instrumented for intravenous drug administration and measurement of MAP. At this time, the cardiovascular effects of angiotensin (Ang) I and AngII (5-20 ng) and sodium nitroprusside (SNP) and acetylcholine (ACh; 1-5 micro g) were assessed. In addition, left ventricular : bodyweight and media : lumen ratios were determined as indices of cardiac and vascular hypertrophy, respectively. 4. Candesartan cilexetil and perindopril alone had minimal effect on MAP when measured both directly and indirectly, whereas direct MAP was significantly decreased in the combined treatment group (131 +/- 6 mmHg; P < 0.05) compared with the vehicle group (156 +/- 9 mmHg). Pressor responses to AngI were significantly decreased in all groups compared with the vehicle-treated group and pressor responses to AngII were significantly decreased in the candesartan cilexetil-treated (P < 0.01) and combined treatment groups (P < 0.01) compared with the vehicle-treated group. Depressor responses to ACh and SNP were not significantly affected by any of the antihypertensive therapies compared with vehicle-treated SHR. 5. Vascular hypertrophy was significantly decreased in the candesartan cilexetil and combined groups compared with the vehicle-treated group, whereas cardiac hypertrophy was reduced, with the rank order of effect being: dual RAS inhibition > perindopril > candesartan cilexetil. Urinary albumin tended to decrease with dual RAS inhibition, but was not significantly affected by this short-term treatment. 6. These results demonstrate the efficacy of low-dose dual RAS inhibition as an antihypertensive modality, at least in SHR, not only in reducing arterial pressure, but also in improving cardiovascular structure.

Combination of low-dose valsartan and enalapril improves endothelial dysfunction and coronary reserve in Nomega-nitro-L-arginine methyl ester-treated spontaneously hypertensive rats

Combination of nonhypotensive doses of valsartan and enalapril markedly improved survival (+87%) compared with untreated animals (37%) in spontaneously hypertensive rats (SHRs) with endothelial dysfunction. However, the combination had no effect on kidney function, and proteinuria persisted over the 12 weeks of the study. It was hypothesized that the greater survival was due to improvement in endothelial function or coronary vasculature despite blockade of nitric oxide synthase and high blood pressure. Therefore, endothelial function was evaluated in isolated aortic ring and maximal coronary blood flow was studied in isolated perfused SHR hearts (20-24 weeks) treated with -nitro-l-arginine methyl ester (L-NAME) (50 mg/l) for 4 weeks. The animals received vehicle, valsartan 5 mg/kg/d, enalapril 1 mg/kg/d, valsartan 50 mg/kg/d, or the combination valsartan 5 mg/kg/d with enalapril 1 mg/kg/d in drinking water. Normotensive Wistar-Kyoto (WKY) rats were used as control. Blood pressure was measured by telemetry. Histopathology was performed on heart, kidney (hematoxylin-eosin), and aorta (Masson trichrome). L-NAME elevated blood pressure by 50 mm Hg after vehicle (199 +/- 5 mm Hg). Valsartan 50 mg/kg/d completely abolished this increase (150 +/- 4 mm Hg) whereas the valsartan-enalapril combination synergistically decreased blood pressure (-37 mm Hg at 162 +/- 7 mm Hg) compared with monotherapy (valsartan 5 mg/kg/d -10 mm Hg; enalapril 1 mg/kg/d -15 mm Hg). All treatments improved the histopathology, most markedly in those receiving the valsartan-enalapril combination. The severity mean grades for lesions were 2.1, 1.9, 1.7, 1.1, and 0.9 in vehicle-treated SHRs, enalapril 1 mg/kg/d, valsartan 5 mg/kg/d, valsartan 5 or 50 mg/kg/d, and the valsartan-enalapril combination, respectively, compared with 0.02 in WKY rats. Acetylcholine-induced relaxation was significantly greater in treated SHRs than after vehicle (-40% at 0.1 mmol acetylcholine) but the combination induced the maximal relaxation (-85%). The ratio of maximal tension induced by serotonin in rings with and without endothelium was 1.4 and 1.3 in vehicle and valsartan 5 mg/kg/d-treated rats whereas it did not differ from 1 in WKY rats and all other treated groups. The cardiac hypertrophy (+27%) was prevented by valsartan 50 mg/kg/d and the valsartan-enalapril combination. Coronary reserve was significantly increased by valsartan 50 mg/kg/d (+85% at 7.8 +/- 0.7 ml/min/g) and the valsartan-enalapril combination (+42% at 6.0 +/- 0.4 ml/min/g) compared with 4.2 +/- 0.5 (vehicle). This was not different of 8.8 +/- 0.5 (WKYs). Despite the maintenance of a high blood pressure, low-dose valsartan-enalapril significantly improved endothelial function and histopathology and increased coronary reserve in SHRs chronically receiving L-NAME.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.

Nipradilol prevents L-NAME-exacerbated nephrosclerosis with decreasing of caspase-3 expression in SHR

The proliferative cell nuclear antigen (PCNA) is an auxiliary protein of DNA polymerase delta and appears to be required for both DNA synthesis and repair. Previously, we showed that prolonged NO synthase (NOS) inhibition produced severe nephrosclerosis with an increase of glomerular cell DNA fragmentation (apoptosis), glomerular ischemia and hypertension in spontaneously hypertensive rats (SHR). The objective of the present study was to investigate the effects of the vasodilating, nonselective, NO-releasing beta-adrenoceptor blocker nipradilol on DNA fragmentation and synthesis/repair of glomerular cells in this prolonged NOS blockaded SHR. Twenty-week-old SHR were administered an NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 80 mg/l in drinking water) or co-treated with the same dose of L-NAME and nipradilol (20 mg/kg/day) for 3 weeks. After this treatment, expression of apoptosis was histologically examined using caspase-3, an apoptosis inducer, in addition PCNA (DNA synthesis/repair), and examination of glomerular morphometric changes, including cell number and tuft area. Nipradilol reduced blood pressure and preserved creatinine clearance reduction in L-NAME/SHR. These effects were associated with normalization of the glomerular cell apoptosis index and caspase-3 score, an increase in PCNA index, and increases in glomerular cell numbers and glomerular tuft area, resulting in a decreased glomerular injury score. Thus, in SHR administered an NOS inhibitor, nipradilol improved nephrosclerosis in association with a decrease in apoptosis and an increase in DNA synthesis/repair of glomerular cells. These findings may provide important insights into DNA repair/repair and apoptosis in nephrosclerosis.

N- and L-type calcium channel antagonist improves glomerular dynamics, reverses severe nephrosclerosis, and inhibits apoptosis and proliferation in an l-NAME/SHR model

OBJECTIVE

To determine the responses of the new dihydropyridine N- and L-type calcium antagonist, cilnidipine, on systemic and renal hemodynamics, glomerular dynamics, renal function, and histopathology in an Nomega-nitro-l-arginine methylester spontaneously hypertensive rat (l-NAME/SHR) model of nephrosclerosis.

METHODS

Five groups of 20-week-old male SHR were studied using renal micropuncture techniques and histopathological analyses: group 1, control; group 2, cilnidipine (10 mg/kg per day) by gavage, for 3 weeks; group 3, l-NAME (50 mg/l) in drinking water, for 3 weeks; group 4, combination of l-NAME and cilnidipine, for 3 weeks; group 5, l-NAME for 3 weeks, followed by cilnidipine for a subsequent 3 weeks.

RESULTS

Cilnidipine significantly reduced mean arterial pressure, total peripheral resistance and renal vascular resistance, while increasing effective renal blood flow and glomerular filtration rate (P < 0.01) in l-NAME/SHR. These hemodynamic changes were associated with significantly increased single nephron glomerular filtration rate (SNGFR) and plasma flow (SNPF) and decreased afferent glomerular arteriolar resistances when cilnidipine was used alone, and with increased SNGFR and SNPF, but decreased glomerular capillary pressure, afferent and efferent arteriolar resistances, urinary protein excretion, serum creatinine and uric acid concentrations (at least P < 0.05) in l-NAME-exacerbated SHR nephrosclerosis. In addition, glomerular and arteriolar injuries were markedly reversed (both P < 0.01), and glomerular apoptosis and cellular proliferation were inhibited and associated with glomerular tuft enlargement and an increase in cell number.

CONCLUSION

Cilnidipine not only prevented, but reversed, the severe renal hemodynamic and glomerular dynamic changes, including apoptosis and glomerular cellular proliferation, in l-NAME/SHR-exacerbated nephrosclerosis. This dual-channel calcium antagonist thus exerted renoprotective pathophysiological effects in the l-NAME/SHR.

Genetic targeting of the renin-angiotensin system for long-term control of hypertension

Although traditional approaches are effective for the treatment and control of hypertension, they have not succeeded in curing the disease, and have therefore reached a plateau. As a result of the completion of the Human Genome Project and the continuous advancement in gene delivery systems, it is now possible to investigate genetic means for the treatment and possible cure for hypertension. In this review we discuss the potential of genetic targeting of the renin-angiotensin system for the treatment of hypertension. We provide examples of various approaches that have used antisense technology with a high degree of success. We focus on our own research, which targets the use of antisense of the angiotensin type I receptor in various models of hypertension. Finally, we discuss the future of antisense technology in the treatment of human hypertension.