Hydrochlorothiazide exacerbates nitric oxide-blockade nephrosclerosis with glomerular hypertension in spontaneously hypertensive rats

Candesartan prevents L-NAME-induced cardio-renal injury in spontaneously hypertensive rats beyond hypotensive effects

Our goal was to assess the cardiovascular and renal protection afforded by angiotensin II type 1-receptor blockade against NG-nitro-L-arginine methyl ester (L-NAME)-exacerbated hypertension in young spontaneously hypertensive rats (SHR), in comparison with the antihypertensive drug, hydralazine. Male SHR were assigned to four groups (n=8 per group): no treatment (controls); L-NAME-treated group (20 mg/kg/day, 10 days, orally); co-treatment with L-NAME and hydralazine (15 mg/kg/day, by gavage); co-treatment with L-NAME and candesartan cilexetil (10 mg/kg/day, by gavage), i.e. at a dose that inhibited acute pressor responses to 5—20 ng angiotensin II. One animal died in the L-NAME group, and tail-cuff systolic blood pressure (SBP) increased significantly compared with controls to 201±5 mmHg. Albumin excretion increased 235-fold in L-NAME-treated rats. Heart weight index averaged 3.5±0.1 and 3.8±0.1 mg/g body weight (p<0.05) in control and L-NAME rats, respectively, indicating moderate cardiac hypertrophy induced by L-NAME. Preglomerular vascular lesions affected 63±6% of interlobular arteries and 10±2% of afferent arterioles (vs. 8±3 and 0.8±0.4% in controls, respectively). Hydralazine and candesartan cilexetil treatment similarly reduced SBP to 153±7, and 165±6 mmHg, respectively. However, candesartan provided more protection, in terms of no significant change in albuminuria (vs. 25-fold increase with hydralazine), regression of cardiac hypertrophy, frequency of vascular lesions and histological indices of renal injury maintained within control values. In conclusion, candesartan cilexetil prevented L-NAME-exacerbated hypertension and associated cardio-renal injury in young SHR, the beneficial effects exceeding those of hydralazine.

Losartan modulates muscular capillary density and reverses thiazide diuretic-exacerbated insulin resistance in fructose-fed rats

The renin-angiotensin system (RAS) is involved in the pathogenesis of insulin sensitivity (IS). The role of RAS in insulin resistance and muscular circulation has yet to be elucidated. Therefore, this study sought to determine the mechanisms of angiotensin II receptor blockers (ARBs) and/or diuretics on IS and capillary density (CD) in fructose-fed rats (FFRs). Sprague-Dawley rats were fed either normal chow (control group) or fructose-rich chow for 8 weeks. For the last 4 weeks, FFRs were allocated to four groups: an FFR group and groups treated with the thiazide diuretic hydrochlorothiazide (HCTZ), with the ARB losartan, or both. IS was evaluated by the euglycemic hyperinsulinemic glucose clamp technique at week 8. In addition, CD in the extensor digitorum longus muscle was evaluated. Blood pressure was significantly higher in the FFRs than in the controls. HCTZ, losartan and their combination significantly lowered blood pressure. IS was significantly lower in the FFR group than in the controls and was even lower in the HCTZ group. Losartan alone or combined with HCTZ significantly increased IS. In all cases, IS was associated with muscular CD, but not with plasma adiponectin or lipids. These results indicate that losartan reverses HCTZ-exacerbated insulin resistance, which can be mediated through the modulation of muscular circulation in rats with impaired glucose metabolism.

Prevalence of hyperuricemia and its association with antihypertensive treatment in hypertensive patients in Taiwan

BACKGROUND

Hyperuricemia is thought to be associated with an increased risk of hypertension, impaired renal function and cardiovascular disease. Our aim is to study the prevalence of hyperuricemia and its association with antihypertensive treatment in Taiwanese hypertensive subjects.

METHODS

We recruited 2145 hypertensive subjects from 19 hospitals in four areas of Taiwan. We assessed the prevalence of hyperuricemia and determined the independent risk factors for raised serum uric acid level by multiple logistic regression analyses.

RESULTS

Compared to the general population, hypertensive subjects in Taiwan had a higher prevalence (mean 35% in males, 43% in females) of hyperuricemia; this prevalence being 1.5- and 1.7-fold higher in males and females respectively. Uric acid levels; gout and prevalence of hyperuricemia were found to be highest in the younger age group (20-39 years) and no regional differences were noted. The most important risk factors for hyperuricemia were impaired renal function and diuretic use. Serum uric acid values correlated significantly with four quintiles of serum creatinine (p<0.0001) independent of diuretic use. Diuretic users had a significantly elevated serum uric acid and serum creatinine values than non-users. Among the patients given diuretics, hyperuricemia occurred in 44% of those given thiazides, in 56% of those given loop diuretics, and in 57% of those given aldosterone receptor blockers.

CONCLUSIONS

Diuretic usage and renal function status have a strong impact on the prevalence of hyperuricemia in Taiwanese hypertensive subjects. It is still unclear, however, whether diuretics induce renal failure through elevating serum uric acid levels.

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.

Uric acid: bystander or culprit in hypertension and progressive renal disease?

In humans, uric acid is the main urinary metabolite of purines. Serum levels are higher compared with other mammalians. Uric acid is an antioxidant and perhaps helps to control blood pressure during a low Na+ diet through stimulation of the renin-angiotensin system. Serum uric acid is also considered a marker of tubular reabsorption and 'effective' circulating blood volume. Moreover, hyperuricemia seems to be a cofactor in Na+ -sensitive hypertension, a marker and possibly itself responsible for microvascular damage through stimulation of the renin-angiotensin system, inhibition of endothelial nitric oxide, and proliferative effects on vascular smooth muscle. As fructose-rich diets increase uric acid levels, hyperuricemia may also play a role in the metabolic syndrome, triggering insulin resistance and hypertension.A number of studies on rats rendered hyperuricemic by administration of uricase inhibitors have recently confirmed induction of arterial hypertension and microvascular injury, particularly in the remnant kidney or in cyclosporine-induced renal fibrosis.

Thiazide-induced subtle renal injury not observed in states of equivalent hypokalemia

Hydrochlorothiazide (HCTZ) is used to manage hypertension and heart failure; however, its side effects include mild hypokalemia, metabolic abnormalities, and volume depletion, which might have deleterious effects on renal and endothelial function. We studied whether HCTZ cause renal injury and/or altered vasoreactivity and if these changes are hypokalemia-dependent. Rats were given a normal diet or a diet moderately low in potassium K+ with or without HCTZ. Animals fed either a low K+ diet alone or HCTZ developed mild hypokalemia. There was no significant difference in systolic blood pressure in the different treatment groups. All three groups with hypokalemia had mild proteinuria; low K(+)-HCTZ rats had reduced creatinine clearance. HCTZ-treated rats displayed hypomagnesemia, hypertriglyceridemia, hyperglycemia, insulin resistance, and hyperaldosteronism. No renal injury was observed in the groups without HCTZ; however, increased kidney weight, glomerular ischemia, medullary injury, and cortical oxidative stress were seen with HCTZ treatment. Endothelium-dependent vasorelaxation was reduced in all hypokalemic groups and correlated with reduced serum K+, serum, and urine nitric oxide. Our results show that HCTZ is associated with greater renal injury for the same degree of hypokalemia as the low K+ diet, suggesting that factors such as chronic ischemia and hyperaldosteronism due to volume depletion may be responsible agents. We also found impaired endothelium-dependent vasorelaxation was linked to mild hypokalemia.

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.

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.

Hypertension and atherosclerosis: clinical implications from the ALLHAT Trial

By failing to recognize the heterogeneity of hypertension, the authors of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) study used a faulty premise to conduct a poorly designed clinical trial. By failing to control blood pressures equally across study drug groups, ALLHAT cannot be considered to be a definitive comparative trial. Being neither a monotherapy trial nor a trial that initiated therapy for blood pressure control, ALLHAT provided no data to recommend first-line therapy for hypertension, making the conclusions invalid. Thiazide-type diuretics increase angiotensin II and consequently promote atherosclerosis and arteriolarsclerosis. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers retard atherosclerosis and are nephroprotective. Multiple randomized controlled trials show beneficial clinical outcomes, including cardioprotection and nephroprotection, with the use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. These agents, and not thiazide-type diuretics, should be used as first-line agents to retard the process of atherosclerosis and its clinical outcomes in the setting of arterial hypertension.

Essential hypertension, progressive renal disease, and uric acid: a pathogenetic link?

Hypertension and hypertension-associated ESRD are epidemic in society. The mechanisms responsible for renal progression in mild to moderate hypertension and those groups most at risk need to be identified. Historic, epidemiologic, clinical, and experimental studies on the pathogenesis of hypertension and hypertension-associated renal disease are reviewed and an overview/hypothesis for the mechanisms involved in renal progression is presented. There is increasing evidence that hypertension may exist in one of two forms/stages. The first stage, most commonly observed in early or borderline hypertension, is characterized by salt-resistance, normal or only slightly decreased GFR, relatively normal or mild renal arteriolosclerosis, and normal renal autoregulation. This group is at minimal risk for renal progression. The second stage, characterized by salt-sensitivity, renal arteriolar disease, and blunted renal autoregulation, defines a group at highest risk for the development of microalbuminuria, albuminuria, and progressive renal disease. This second stage is more likely to be observed in blacks, in subjects with gout or hyperuricemia, with low level lead intoxication, or with severe obesity/metabolic syndrome. The two major mechanistic pathways for causing impaired autoregulation at mild to moderate elevations in BP appear to be hyperuricemia and/or low nephron number. Understanding the pathogenetic pathways mediating renal progression in hypertensive subjects should help identify those subjects at highest risk and may provide insights into new therapeutic maneuvers to slow or prevent progression.

Differential effects of antihypertensive drugs on renal and glomerular hemodynamics and injury in the chronic nitric-oxide-suppressed rat

BACKGROUND/AIMS

Prolonged nitric oxide synthase (NOS) inhibition with N(omega)-nitro-L-arginine methylester in normotensive and hypertensive rats has been demonstrated to produce severe systemic and glomerular hypertension with glomerular sclerosis, and these changes have become a useful experimental model of hypertensive nephrosclerosis. This review summarizes data from our serial studies as well as work of others who are also investigating the effects of the commonly used antihypertensive drugs (including calcium antagonist, angiotensin-converting enzyme inhibitor, angiotensin II type 1 receptor blocker, aldosterone antagonist and thiazide diuretic) on renal and glomerular hemodynamics, renal function and glomerular histopathology using this model.

METHODS

A Medline search was performed to identify the relevant literature describing renal effects of antihypertensive drugs in models of hypertension and nephrosclerosis produced or exacerbated by NOS inhibition.

RESULTS

Existing data have indicated that most of these drug classes have produced dramatic renoprotective effects, structurally or functionally, on nephrosclerosis induced by prolonged NOS inhibition.

CONCLUSION

This review of experimental studies has provided strong evidence supporting the clinical benefits of antihypertensive drugs for hypertensive patients with renal impairment particularly those with endothelial dysfunction associated with NOS deficiency.

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.

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.

Apoptosis and glomerular injury after prolonged nitric oxide synthase inhibition in spontaneously hypertensive rats

This study was designed to investigate the relationship between apoptosis and glomerular injury in spontaneously hypertensive rats (SHR) with hypertensive disease that was exacerbated by inhibition of NO synthesis. Development of glomerular cell apoptosis was evaluated by assessment of renal hemodynamics, glomerular morphometric changes, and participation of the renin-angiotensin system. Three groups of 20-week-old SHR were investigated: control male SHR and 2 similar groups given 2 doses of N(G)-nitro-L-arginine methyl ester (L-NAME, 50 or 80 mg/L, respectively) for 3 weeks. Mean arterial pressure and renal vascular resistance increased, whereas effective renal plasma flow and glomerular filtration rate were diminished by L-NAME. The small artery wall/lumen ratio increased as the glomerular-tuft area diminished. Renal cortical tissue levels of angiotensin II increased in response to the L-NAME, thereby inducing afferent arteriolar injury. Apoptosis and proliferative index (PCNA) of nonsclerotic glomeruli were induced by the low-dose L-NAME as the glomerular cell number decreased. In contrast, the PCNA index was downregulated with the high-dose L-NAME. These results indicate that angiotensin II activation, induced by L-NAME, was related to glomerular cell deletion and apoptosis together with the pathophysiological changes of severe nephrosclerosis and impaired renal dynamics.

Local Hemodynamic Changes in Hypertension

As a result of antihypertensive therapy, there has been a remarkable decrease in morbidity and mortality from such cardiovascular endpoints as stroke, coronary heart disease, and major hypertensive emergencies. In contrast, there has been no relenting in the increasing prevalence of cardiac failure and end-stage renal disease (ESRD) associated with hypertensive cardiovascular disease. Recent experience in our laboratories that involved the natural development of the cardiac and renal hemodynamic alterations in spontaneously hypertensive rats demonstrated that the natural history and pathophysiological lesions associated with cardiac failure and ESRD may be vastly different from the heretofore more pressure-dependent brain and other cardiac endpoints reported in earlier years. These initial antihypertensive agents (eg, diuretics, β-adrenergic receptor inhibitors) had minimal anti-ischemic and antifibrotic effects on heart and kidney and did not exert the cardiac and nephroprotective hemodynamic effects of the newer classes of agents. The cardiac and renal endpoints resulting in organ failure today are more related to ischemia, intraorgan fibrosis, and aging. Our experimental studies summarized herein strongly suggest that the newer classes of antihypertensive drugs (ie, ACE inhibitors, angiotensin II type 1 receptor antagonists, certain calcium antagonists, and perhaps l -arginine) may reverse these pathophysiological lesions through improving blood flow and flow reserve, their antifibrotic and other actions. To this end, we look forward to the results of ongoing, well-controlled, and prospectively conducted multicenter clinical studies designed to demonstrate prevention of cardiac and renal failure.

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

This study was conducted to determine potentially differential effects between an angiotensin II type 1 (AT(1)) receptor antagonist and an ACE inhibitor on systemic, renal, and glomerular hemodynamics and pathological changes in spontaneously hypertensive rats (SHR) with N(omega)-nitro-L>-arginine methyl ester (L-NAME)-exacerbated nephrosclerosis. The hemodynamic, renal micropuncture, and pathological studies were performed in 9 groups of 17-week-old male SHR treated as follows: group 1, controls (n=16); group 2, candesartan (10 mg/kg per day for 3 weeks) (n=7); group 3, enalapril (30 mg/kg per day for 3 weeks) (n=8); group 4, candesartan (5 mg/kg per day) plus enalapril (15 mg/kg per day for 3 weeks) (n=9); group 5, L-NAME (50 mg/L in drinking water for 3 weeks) (n=17); group 6, L-NAME (50 mg/L) plus candesartan (10 mg/kg per day for 3 weeks) (n=7); group 7, L-NAME (50 mg/L) for 3 weeks followed by candesartan (10 mg/kg per day) for another 3 weeks (n=8); group 8, L-NAME (50 mg/L) plus enalapril (30 mg/kg per day for 3 weeks) (n=7); and group 9, L-NAME (50 mg/L) plus enalapril (30 mg/kg per day) and the bradykinin antagonist icatibant (500 microg/kg SC per day via osmotic minipump for 3 weeks) (n=7). Both candesartan and enalapril similarly reduced mean arterial pressure and total peripheral resistance index. These changes were associated with significant decreases in afferent and efferent glomerular arteriolar resistances as well as glomerular capillary pressure. Histopathologically, the glomerular and arterial injury scores were decreased significantly, and left ventricular and aortic masses also were diminished significantly in all treated groups. L-NAME-induced urinary protein excretion was prevented by both candesartan and enalapril. Thus, both AT(1) receptor and ACE inhibition prevented and reversed the pathophysiological alterations of L-NAME-exacerbated nephrosclerosis in SHR. Itatibant only blunted the antihypertensive effects of enalapril but did not attenuate the beneficial effects of ACE inhibition on the L-NAME-induced nephrosclerosis. Thus, the AT(1) receptor antagonism and ACE inhibition have similar renal preventive effects, which most likely were achieved through reduction in the effects of angiotensin II, and ACE inhibition of bradykinin degradation demonstrated little evidence of renoprotection.

Predisposition of spontaneously hypertensive rats to develop renal injury during nitric oxide synthase inhibition

Chronic nitric oxide (NO) synthase (NOS) inhibition results in renal injury. Hypertension is an important risk factor for renal injury. We studied the influence of preexistent hypertension on the sensitivity for renal injury induced by chronic NOS inhibition in rats. Spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with 3, 10, 30 and 100 mg/l Nomega-nitro-L-arginine (L-NNA) until death. Systolic blood pressure and proteinuria were measured regularly and compared with time-control measurements in untreated SHR and WKY. In WKY, 3 and 10 mg/l L-NNA did not affect systolic blood pressure, while 30 and 100 mg/l L-NNA resulted in an increase in systolic blood pressure after 12 and 4 weeks, respectively. In contrast in SHR, every dose of L-NNA resulted in an increase in systolic blood pressure after 2 weeks. In WKY, 3 and 10 mg/l L-NNA did not affect proteinuria or survival, while 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30 and 9 weeks, and a median survival of 36 and 12 weeks, respectively. In SHR, 3, 10, 30 and 100 mg/l L-NNA resulted in an increase in proteinuria after 30, 12, 3 and 3 weeks, and a median survival of 41, 20, 5 and 3 weeks, respectively. Thus, at every dose of the inhibitor, chronic NOS inhibition resulted in far earlier increases in systolic blood pressure and proteinuria and a marked increase in mortality in SHR as compared to WKY. Indeed, a very low dosage of L-NNA that caused no harm in WKY was followed by marked increases in proteinuria and blood pressure and decreased survival in SHR. Hypertension strongly increases the vulnerability to cardiovascular risk factors that compromise the NO-system.

Combination of non-hypotensive doses of valsartan and enalapril improves survival of spontaneously hypertensive rats with endothelial dysfunction

There is increasing evidence to suggest endothelial dysfunction as a critical factor in vascular diseases. Genetically predisposed spontaneously hypertensive rats (SHR) treated with inhibitors of nitric oxide (NO) synthase, develop a severe hypertensive nephrosclerosis without the necessity for surgical reduction in renal mass, nephrectomy, renal infarction or nephrotoxic drugs. In these animals, endothelial dysfunction is considered a valid model for assessment of the efficacy of cardiovascular therapy. SHR were treated with either the angiotensin-converting enzyme inhibitor enalapril or the angiotensin II (Ang II) AT(1)-receptor antagonist (AIIA) valsartan at sub-hypotensive doses and the effects on survival rates, cardiac and renal changes were monitored. Rats treated with valsartan, alone or in combination with enalapril, showed markedly higher survival rates (67-85%, respectively) than untreated animals (37%) or those treated with enalapril alone (55%). Valsartan at a dose which attenuated blood pressure increase led to even greater survival rates (95%). Despite these improved survival rates, at non-hypotensive doses the drugs had no effect on histological appearance, nor was kidney function improved. Plasma creatinine levels were reduced by valsartan, alone or in combination with enalapril, but proteinuria persisted with all treatments over the 12 weeks of the study. Aldosterone levels were significantly reduced by all treatments. The results suggest a beneficial role for endothelium in hypertension. Reduced renal perfusion pressure probably underlies the beneficial renal effects of high-dose valsartan.

The necessity for recognition and treatment of patients with "mild" hypertension

A dramatic evolution has occurred in the past four decades in our underlying knowledge of pathophysiology of the hypertensive diseases and in the availability of myriad pharmacologic agents for control of hypertension. This report provides a current review of antihypertensive treatment interspersed with personal opinions supported by appropriate references. It focuses on the recent national recommendations dealing with the prevention, detection, evaluation and treatment of the disease (JNC-6). Whereas I believe that the height of arterial pressure is of primary importance, it is not the sine qua non explaining all target organ involvement or complications of hypertensive disease. Consequently, all that is classified today as Stages 1 and 2 hypertension (old terminology: "mild" and "moderate") in terms of blood pressure elevation does not explain all outcomes of disease. Indeed, JNC-6 introduced the new concept of risk stratification for therapy based not only on the height of systolic and diastolic pressure but also on the presence of target organ involvement, comorbidity and other risk factors. However, after considerable advances since the inception of the National High Blood Pressure Education Program (NHBPEP) in 1972, it appears that we are avoiding our responsibilities and reversing our gains. It is of vital importance that we renew our efforts to identify, evaluate and treat all patients with hypertension; this is especially so for the vast numbers of patients with Stages 1 and 2 hypertension.

Apoptosis, coronary arterial remodeling, and myocardial infarction after nitric oxide inhibition in SHR

This study was designed to investigate the relationship between apoptosis (programmed cell death) and coronary arterial remodeling in spontaneously hypertensive rats (SHR) following prolonged nitric oxide synthesis inhibition. In addition, we evaluated whether the development of coronary arterial smooth muscular cell apoptosis was related to hemodynamics or to vascular hypertrophy. Three groups of 20-week-old male SHR were investigated: controls, and two groups that received two doses of N(G)-nitro-L arginine (L-NAME, 50 mg/L and 80 mg/L) each for 3 weeks. Mean arterial pressure and total peripheral resistance index increased whereas cardiac index diminished with L-NAME. Pathohistological study demonstrated increased pericardiac fibrosis and coronary arterial injury score in the L-NAME group in a dose-dependent manner. The high dose of L-NAME (Group 3) produced myocardial infarction in 78% of the rats. The wall:lumen ratio of epicardial coronary arteries was greater in L-NAME treated SHR (0.23+/-0.02 versus 0.16+/-0.02; P<0.05) and was associated with markedly increased apoptosis (15.3+/-6 versus 1. 9+/-1; P<0.05) without smooth muscle cell proliferation (PCNA positive cells). Apoptosis occurred predominantly in hypertrophic coronary arterial smooth muscular cells; myocardial infarction and ventricular fibrosis were exacerbated by impaired hemodynamics induced by L-NAME. These data suggest that coronary endothelial dysfunction and myocardial ischemic disease induced by L-NAME were responsible for apoptosis of coronary arterial smooth muscle cells, myocardial fibrosis, and infarction, all pathological findings that are consistent with what may be found in clinical hypertensive heart disease.

Differential effects of T- and L-type calcium antagonists on glomerular dynamics in spontaneously hypertensive rats

To determine whether there is a difference in the effects of T- and L-type calcium antagonists on systemic, renal, and glomerular hemodynamics, the pathological changes of N(G)-nitro-L-arginine methyl ester (L-NAME)-exacerbated nephrosclerosis and clinical alterations were investigated in spontaneously hypertensive rats (SHR). Seven groups of 17-week-old male SHRs were studied: Group 1, control; Group 2, mibefradil, 50 mg. kg(-1). d(-1); Group 3, L-NAME in drinking water, 50 mg/L; Group 4, L-NAME (50 mg/L) plus mibefradil (50 mg. kg(-1). d(-1)); Group 5, L-NAME (50 mg/L) plus amlodipine (10 mg. kg(-1). d(-1)); Group 6 and 7, L-NAME (50 mg/L) for 3 weeks followed by mibefradil (50 mg. kg(-1). d(-1)) or amlodipine (10 mg. kg(-1). d(-1)), respectively, for the subsequent 3 weeks. Both the T- and L-channel calcium antagonists similarly reduced mean arterial pressure and total peripheral resistance index. These changes were associated with significant decreases in afferent and efferent glomerular arteriolar resistances and the ultrafiltration coefficient (P<0.01). Furthermore, the histopathological glomerular and arterial injury scores and urinary protein excretion were also significantly improved (P<0.01), and left ventricular and aortic masses were significantly diminished in all treated groups. Both drugs, mibefradil and amlodipine, had effects of increasing the single-nephron glomerular filtration ratio (SNGFR), and single-nephron plasma flow (SNPF), and of reducing glomerular afferent arteriolar resistance and urinary protein excretion. Thus, the T-type (mibefradil) and L-type (amlodipine) calcium antagonists each prevented and reversed the pathophysiological alterations of L-NAME-exacerbated hypertensive nephrosclerosis in SHR. The T-type calcium antagonist (mibefradil) seemed to have been more effective than the L-type amlodipine antagonist and it produced a greater reduction in afferent arteriolar resistance while preserving SNGFR.

Long-term furosemide treatment in the normal rat: dissociation of glomerular hypertrophy and glomerulosclerosis

Furosemide treatment produces glomerular hypertrophy and augments glomerular capillary hydraulic pressure in the normal rat. Similar processes have been implicated in the progression of glomerulosclerosis (GS). Whereas prior experiments with furosemide treatment of 6 to 8 weeks duration have produced no detrimental effects on renal function or structure, the effects of more prolonged treatment are unknown. Male Munich-Wistar rats were pair fed with or without furosemide, 40 mg/d, from the time of weaning through 10 months of age. At selected time points, 24-hour urine collections were obtained for total protein and volume determination. At the end of the study, light and electron microscopic morphometric studies were performed. Renal cortical hypertrophy and glomerular hypertrophy were sustained throughout the 9 months of treatment in the group receiving furosemide. The cortical interstitial area was increased in the furosemide group, but this did not appear to be the result of fibrosis. Proximal and distal tubule diameter were unaffected by treatment. No differences in GS or glomerular ultrastructure were shown. This study provides no evidence of detrimental glomerular effects of furosemide in normal animals. Further studies of furosemide treatment under conditions of preexisting renal pathological conditions are warranted to confirm the safety of this treatment in situations analogous to those seen in the clinical setting. Interstitial expansion also warrants further study in this setting.

Therapeutic implications and new perspectives for essential hypertension and renal damage

The kidney can suffer the consequences of a persistently elevated blood pressure. In fact end-stage renal failure caused by essential hypertension appears to be one of the most prevalent etiologies in patients entering a dialysis program. Blood pressure control is needed in order to prevent the progressive loss of renal function. Target blood pressure control has been established at values as low as 125/75 mm Hg for patients with proteinuria above 1 g/day. Attainment of this target level usually requires the combination of two or more drugs. However, the possibility that differences exist among the different classes of antihypertensive drugs beyond their capacity to simply lower blood pressure remains to be clearly elucidated. The fact that the presence of chronic renal failure is also accompanied by an enhanced cardiovascular risk potentiates the need to explore the renoprotective and cardiovascular protective capacity of the different classes of antihypertensive drugs, in patients with essential hypertension and some degree of renal involvement, characterized by the presence of microalbuminuria, proteinuria and/or an elevated serum creatinine.

Chronic administration of furosemide augments renal weight and glomerular capillary pressure in normal rats

Angiotensin II (ANG II) is believed to promote progressive renal injury via augmented glomerular capillary hydraulic pressure (PGC). Acute volume reduction secondary to diuretic administration increases circulating ANG II and augments PGC, yet the hemodynamic effects of sustained diuretic administration are unknown. Therefore, glomerular micropuncture studies were performed in male Munich-Wistar rats after 6-8 wk of treatment with daily furosemide (F, 40 mg/day), furosemide plus the AT1 receptor antagonist, losartan (F + L, 5 mg/day), or no therapy (C, control). Renal weight was increased in F rats (1.23 +/- 0.7 g) vs. C (1.00 +/- 0.06 g) or F + L (0.97 +/- 0.01 g). In addition, PGC was elevated in F animals (52.1 +/- 1.5 mmHg) vs. C (43.7 +/- 1.5) or F + L-treated rats (41.3 +/- 1.7). F-treated rats were also characterized by a relative increase in efferent arteriolar resistance and filtration fraction. The latter was markedly attenuated in F + L-treated animals. Collectively, these findings are consistent with an ANG II-mediated alteration in intrarenal hemodynamics. In contrast to acute volume manipulations, however, chronic furosemide augmented renal growth, whereas losartan administration completely arrested this phenomenon. Further studies are warranted to determine whether the hemodynamic and growth adaptations elicited by chronic F administration induce or accelerate renal injury.

Nephroprotective effect of antihypertensive drugs in essential hypertension

BACKGROUND

Effective antihypertensive treatment has prevented target-organ involvement in hypertension, markedly reducing morbidity and mortality from strokes, coronary heart disease, cardiac failure, and hypertensive emergencies. However, the incidence of hypertension-related end-stage renal disease continues to increase, suggesting that therapeutic reduction in arterial pressure by itself is not sufficient to prevent the development of hypertensive renal failure.

OBJECTIVE

To examine experimental and clinical data concerning the protective effect of reduction of arterial pressure on the progression of hypertension-related renal disease, and the evidence indicating that some antihypertensive agents may afford more nephroprotection, over and above that attributable to reduction of arterial pressure.

RESULTS

Results of numerous studies clearly indicate that adequate control of arterial pressure, irrespective of the antihypertensive agent used, slowed the progression of renal disease. Results of some studies suggest that lowering arterial pressure below the level that is usually considered adequate has an additional beneficial effect by slowing the progression of renal injury.

CONCLUSION

Results of a number of studies evaluating nephroprotective effects of various drugs and regimens have indicated that certain agents, most notably angiotensin converting enzyme inhibitors and their combination with calcium antagonists, afford more protection than do others at similar levels of reduction of arterial pressure. Results of still other studies suggest that certain agents that exert greater nephroprotection are more efficient at controlling arterial pressure. Therefore, further data are needed before any final conclusion can be drawn. However, it is clear that, in order to establish nephroprotection in patients with essential hypertension, the problem should not be further complicated by additional comorbid diseases such as diabetes mellitus.

Renoprotective effects of felodipine and/or enalapril in spontaneously hypertensive rats with and without L-NAME

To determine the renoprotective effects of a calcium antagonist (felodipine) and an angiotensin-converting enzyme (ACE) inhibitor (enalapril), alone or in combination, 10 groups of 19-week-old spontaneously hypertensive rats (SHR) (with or without N(G)-nitro-L-arginine methyl ester [L-NAME]) were studied using renal micropuncture techniques. Group 1 (control), group 2 (felodipine, 30 mg x kg(-1) x d[-1]), group 3 (enalapril, 30 mg x kg(-1) x d[-1]), and group 4 (felodipine plus enalapril, 15 mg x kg(-1) x d(-1) each agent) were studied after 3 weeks of treatment without L-NAME. L-NAME (50 mg/L) cotreatment was administered in drinking water to groups 6 through 10 using the same doses of each agent as in groups 1 through 4: group 5 (only L-NAME), group 6 (felodipine), group 7 (enalapril), and group 8 (felodipine plus enalapril). Groups 9 and 10 received L-NAME initially for 3 weeks followed by felodipine or felodipine plus enalapril, respectively, for the subsequent 3 weeks. All three treatments resulted in reductions in mean arterial pressure and total peripheral vascular resistance (P<.001) that were associated with important structural and functional renal microcirculatory improvements. Thus, the pathological nephrosclerosis (subcapsular and juxtamedullary) glomerular and arteriolar injury scores were improved (P<.05 at least) in association with normalization of afferent and efferent arteriolar resistances, and single-nephron glomerular filtration rate, plasma flow, and blood flow were significantly improved, as well as the ultrafiltration coefficient (compared with group 5, L-NAME). Thus, the calcium antagonist felodipine, alone or in combination with an ACE inhibitor, not only prevented but also reversed L-NAME-exacerbated hypertensive nephrosclerosis in SHR.

Nephrosclerosis and hypertension

In patients with benign nephrosclerosis, the histologic changes are characterized by hyaline degeneration of afferent arterioles with reduced kidney size. Although the glomeruli are nearly intact in patients with adult essential hypertension, the greatest numbers of sclerotic glomeruli are seen in nephrosclerosis with the aging process. Aging undoubtedly plays a role. In the authors' experience, the kidney of an elderly subject, although with normotensive pressure and normal level of cholesterol, shows an increased mesangial matrix and hypertrophic vascular medial smooth muscle cells. Kidneys of elderly subjects also are associated with a large number of sclerotic glomeruli. Experimental evidence supports the notion that the pathogenesis of glomerulosclerosis with nephrosclerosis has been demonstrated as important factors: (1) the elevation of PG (glomerular hypertension); (2) mesangial dysfunction, such as mesangiolysis and increased mesangial matrix; and (3) genetic abnormalities (apoptosis) in mesangial cells with glomerular hypertension. Malignant nephrosclerosis is characterized histologically by vascular endothelial damage and fibrinoid necrosis of afferent and interlobular arteries. In an afferent arteriole or a glomerulus, NOS or endothelin produced in endothelial cells may play a role in the reduction or the maintenance of vascular tone. The frequency of malignant hypertension has decreased because of the effective treatment of essential hypertension with new antihypertensive agents: calcium antagonists, ACE inhibitors, and angiotensin II receptor antagonists. Therefore, the importance of the prevention of essential hypertension with these antihypertensive agents, by slowing and stopping the increase in blood pressure from mild hypertension, has received widespread recognition in the prevention of organ damage, such as cases of cardiovascular disease and ESRD. Thus, prevention of renal injuries is an important goal of antihypertensive therapy.

Current clinical pathophysiologic considerations in essential hypertension

Over the years, much has been learned from unraveling the pathophysiological alterations associated with the hypertensive diseases. Despite this large base of fundamental and clinical information, our knowledge continues to expand. This article discusses the multifactorial nature of hypertensive disease, including the vascular and cardiac participation in the elevation of arterial pressure and in target organ involvement by the disease. Some of the most exciting advances of the last decade are summarized in this review.

The kidney in blood pressure regulation and development of hypertension

Systemic arterial pressure is a dynamic and responsive physiologic parameter that can be influenced by many different factors. In particular, short-term changes in arterial pressure are caused by a myriad of mechanisms that affect cardiac output, total peripheral resistance, and cardiovascular capacitance. In the long run, however, most of these actions can be buffered or compensated by appropriate renal adjustments of sodium balance, ECFV, and blood volume. As long as the mechanisms regulating sodium excretion can maintain sodium balance by appropriately modulating the sensitivity of the pressure-natriuresis relationship, normal arterial pressure can be sustained. Derangements that compromise the ability of the kidneys to maintain sodium balance, however, can result in the kidney's need for an elevated arterial pressure to reestablish net salt and water balance.

Arthus C. Corcoran Memorial Lecture. Influence of nitric oxide and angiotensin II on renal involvement in hypertension

Remarkable advances have been made with prolonged antihypertensive therapy in reversing cardiovascular morbidity and mortality. Deaths from stroke have been reduced by 70% and from coronary heart disease by 35%. In contrast, endstage renal disease resulting from hypertension continues to increase. The explanations for this seeming paradox remain unresolved even though experimental models have demonstrated that certain antihypertensive agents may have beneficial renal and intrarenal hemodynamic effects; but reversal of the intrarenal pathological lesions have not been shown to improve. This discussion summarizes recent studies from our laboratory in aged (73- and 85-week-old) spontaneously hypertensive rats (SHR) with naturally occurring end-stage renal disease and in a model of aged SHR employing nitric oxide inhibition in younger, adult (20-week-old) SHR. Our findings demonstrated that the systemic and whole renal hemodynamics, intrarenal glomerular dynamics, proteinuria, and renal pathological lesions can be prevented or reversed with angiotensin-converting enzyme inhibition therapy but not with hydrochlorothiazide (at similar levels of arterial pressure reduction). The implications and possible mechanisms involved in the development of both naturally occurring and nitric oxide-exacerbated SHR are multifactorial, involving the endothelial nitric oxide system and its interaction with angiotensin II (and possibly bradykinin) among other factors. Moreover, these pathophysiological cellular mechanisms may be shared by the aging process as well as in naturally occurring spontaneous hypertension in the rat and, perhaps, in humans with essential hypertension. Thus, antihypertensive therapy seems to be specific in its ability to prevent and even reverse the pathophysiological derangements of renal involvement in hypertension. Thus, prevention and reversal of end-stage renal disease do not seem to require greater reduction of arterial pressure than with other target-organ involvement. However, they do require specific inhibition of the arteriolar and glomerular lesions produced by the disease.