Reduction of sympathetic hyperactivity by enalapril in patients with chronic renal failure

Pathogenesis and treatment of hypertension in polycystic kidney disease

PURPOSE OF REVIEW

Hypertension is common in patients with autosomal dominant polycystic kidney disease. It may contribute to cardiovascular risk and to progression of renal failure.

RECENT FINDINGS

Apart from fluid overload and renin activation, hypertensive patients with autosomal dominant polycystic kidney disease also have increased sympathetic activity, regardless of renal function. Sympathetic hyperactivity not only contributes to the hypertension but may also increase cardiovascular risk independent of blood pressure.

SUMMARY

Treatment for normalizing blood pressure and sympathetic activity should be started early in the course of the disease.

Heart rate in hypertensive patients treated with ACE inhibitors and long-acting dihydropyridine calcium antagonists

Rapid heart rate (HR) has been reported to be a predictor of cardiovascular morbidity and mortality in hypertensive patients. The aim of this study was to evaluate the effect of ACE inhibitors and long-acting dihydropyridine calcium antagonists on clinic and ambulatory HR in patients with essential hypertension. We selected 292 hypertensive patients treated with ACE inhibitors and 198 hypertensive patients treated with dihydropyridine calcium antagonists. Groups were balanced for age, gender, body mass index, baseline blood pressure (BP) and HR, treatment duration and occupation. Patients had been submitted to clinic evaluation and noninvasive monitoring of BP and HR at baseline and during chronic therapy. Clinic and ambulatory BP were significantly and similarly reduced in patients treated with ACE inhibitors and calcium antagonists. Globally, clinic and 24-h HR were significantly reduced in patients treated with ACE inhibitors and remained unchanged in those treated with calcium antagonists. When patients were grouped according to baseline clinic HR (< 65 beats/min, 65-74 beats/min, 75-84 beats/min, and >85 beats/min), ACE inhibitors did not significantly change HR in subjects with baseline clinic HR <74 beats/min but significantly reduced clinic, 24-h, daytime and nighttime HR in those with baseline HR >75 beats/min and particularly in those with baseline HR >85 beats/min. Calcium antagonists did not significantly change clinic, 24-h, daytime and nighttime HR in various subgroups. Our study shows that ACE inhibitors reduce both clinic and ambulatory HR in hypertensive patients with faster HR, who seem to be at higher risk, and that long-acting dihydropyridine calcium antagonists do not induce significant changes in HR during chronic treatment (neither decrease nor increase). Whether this aspect is associated with a better prognostic impact of ACE inhibitors in essential hypertension should be determined in prospective studies.

A novel association between residual renal function and left ventricular hypertrophy in peritoneal dialysis patients

BACKGROUND

Left ventricular hypertrophy (LVH) and dialysis adequacy are both important predictors for mortality in dialysis patients. This study evaluated the association between residual renal function (RRF) and the severity of LVH in endstage renal failure (ESRF) patients undergoing long-term continuous ambulatory peritoneal dialysis (CAPD).

METHODS

A cross-section study was performed with left ventricular mass index (LVMi), determined in 158 non-diabetic CAPD patients using echocardiography and its relationship with residual glomerular filtration rate (GFR), peritoneal dialysis (PD) and total weekly urea clearance (Kt/V) and other known risk factors for LVH was evaluated.

RESULTS

Twelve patients had no LVH (group I). The remaining 146 patients were stratified [group II (lowest), III and IV (highest)] according to the LVMi (median 207 g/m2; range 103 to 512 g/m2). Across the four groups of patients with increasing LVMi, there was significant decline in GFR (2.27 +/- 1.98 vs. 1.49 +/- 1.58 vs. 1.61 +/- 1.91 vs. 0.80 +/- 1.42 mL/min/1.73 m2; P = 0.011) and total weekly Kt/V (1.98 +/- 0.44 vs. 1.96 +/- 0.38 vs. 1.92 +/- 0.42 vs. 1.71 +/- 0.42; P = 0.037); however, PD Kt/V was similar for all four groups. Patients with better-preserved residual GFR not only had significantly higher total Kt/V, but were less anemic and hypoalbuminemic and had a trend toward lower systolic blood pressure and arterial pulse pressure. Multiple regression analysis showed that other than age, gender, body weight, arterial pulse pressure, hemoglobin and serum albumin, known factors for LVH, residual GFR (estimated mean -7.94; 95% confidence interval -15.13 to -0.74; P = 0.031) was also independently associated with LVMi.

CONCLUSIONS

Other than anemia, hypoalbuminemia and arterial pulse pressure, this study demonstrates an important, novel association between the degree of RRF and severity of LVH in ESRF patients undergoing long-term CAPD. Prospective studies are needed to define if indeed there is a cause-effect relationship between this association, to evaluate if a decline in residual GFR is independently associated with an increase in LVMi, and to determine whether treatment directed at preserving RRF will reduce the severity of LVH, improve cardiac performance and hence survival of these patients.

Norepinephrine and concentric hypertrophy in patients with end-stage renal disease

We have recently observed that in patients with end-stage renal disease (ESRD) raised plasma norepinephrine (NE) is an independent predictor of incident cardiovascular events but that its prognostic power is reduced when this sympathetic marker is tested in statistical models including also left ventricular mass. Because left ventricular hypertrophy (LVH) may be a mechanism whereby NE contributes to the high rate of cardiovascular events in ESRD, we examined the relationship between plasma NE and echocardiographic parameters of left ventricle mass in a large group of ESRD patients. Mean wall thickness (MWT) was higher in patients in the third NE tertile than in the other 2 tertiles (P=0.001), and such an increase was paralleled by a rise in relative wall thickness (RWT) (P=0.006). Concentric LVH was more prevalent in patients in the third NE tertile (46%) than in the second (38%) and first (25%) NE tertiles. Multivariate regression analysis confirmed that the association of plasma NE with the muscular component of left ventricle (MWT) and with RWT was independent (P< or =0.001) of other cardiovascular risk factors, and in these models, plasma NE ranked as the second correlate of MWT and RWT. Similarly, multiple logistic regression analysis showed that the association of plasma NE with concentric LVH was strong and again independent of other risk factors (P=0.003). Plasma NE is associated to concentric LVH in ESRD patients. These observations constitute a sound basis for testing the effect of anti-adrenergic drugs on left ventricle mass and on cardiovascular outcomes in patients with ESRD.

Vascular maternal reactivity and neonatal size in normal pregnancy

OBJECTIVE

The purpose of the present study was to determine the associations of cold pressor test (CPT) cardiovascular reactivity with gestational age at birth and neonatal size in normotensive pregnant women.

METHODS

Seventy (70) healthy pregnant women were enrolled. The CPT consisted of introducing the patients' hands in cold water (4 degrees C) for 3 min. An automatic oscillometric device was used to record blood pressure (BP) every minute for the following 5 min. Perinatal results were correlated with CPT findings.

RESULTS

Vascular reactivity assessed by CPT was higher in pregnant hypertensive women and in women with a hypertensive family history. Mean BP increases caused by CPT showed a significant negative correlation for gestational age (r = -0.58, p < 0.001) and cephalic perimeter (r = -0.57, p = 0.03). Diastolic BP increases caused by CPT were negatively correlated with newborn weight (r = -0.78, p < 0.001). Predictable newborn weight, gestational age, and cephalic perimeter were 4046 (47 x diastolic BP increase), 40.2 (0.07 x mean BP increase), and 35.8 (0.09 x mean BP increase), respectively.

CONCLUSIONS

Results show that every mm Hg diastolic BP increase in response to CPT was correlated with a 47-g decrease in the newborn normal weight. Furthermore, every mean mm Hg BP increase in response to CPT was associated with a 0.07-week decrease in the newborn normal gestational age and a 0.09-cm decrease in the normal cephalic perimeter at birth.

Effects of selective angiotensin II receptor blockade on sympathetic nerve activity in primary hypertensive subjects

OBJECTIVE

The role of the renin-angiotensin system in the regulation of sympathetic nervous activity in human hypertension was evaluated in patients with moderate primary hypertension. For that purpose, the effects of selective angiotensin II (ANG II) receptor blockade by valsartan on sympathetic outflow to the muscle vascular bed and hemodynamic parameters were examined. Results were compared with the effects of the peripherally acting calcium antagonist amlodipine.

DESIGN

Eighteen hypertensive but otherwise healthy subjects were examined in a double-blind, placebo-controlled, cross-over protocol receiving either valsartan or amlodipine or placebo for 7 days in a randomized sequence. Treatment periods were separated by washout periods of 2 weeks.

METHODS

At the seventh day of treatment, blood pressure, heart rate, muscle sympathetic nerve activity (MSNA), norepinephrine, renin and angiotensin were measured during resting conditions. Additionally, parameters were measured after administration of negative pressure of -15 mmHg to the lower part of the body and after a cold pressor test.

RESULTS

Both antihypertensive drugs significantly decreased oscillometrically measured systolic blood pressure and diastolic blood pressure without any difference in effect. While valsartan did not affect the heart rate at rest, amlodipine increased it significantly. Likewise, MSNA was significantly enhanced by amlodipine but not by valsartan. Only ANG II receptor blockade increased renin and angiotensin levels.

CONCLUSIONS

Selective ANG II receptor blockade not only decreases blood pressure, but also shifts the baroreflex set-point for the initiation of counter-regulatory reflex responses of heart rate and blood pressure towards normal blood pressure levels. Thus, data suggest that ANG II plays a pathogenetic role in the elevation of the baroreflex set point in primary hypertensive subjects.

Sympathetic nervous system function in renal hypertension

Hypertension is a common complication of chronic renal failure, accelerating the deterioration in renal function and constituting an important risk factor for the excessive cardiovascular morbidity and mortality. However, there are large gaps in our understanding of the pathogenesis and treatment of renal hypertension. Although this hypertension traditionally is thought to be largely volume dependent, an increasing body of literature suggests that there is an important sympathetic neural component. Microneurographic studies have demonstrated sympathetic overactivity without baroreflex impairment in both hypertensive chronic hemodialysis patients as well as in those with less advanced renal insufficiency. In a small group of patients with moderate chronic renal insufficiency and renin-dependent hypertension, sympathetic overactivity was normalized during antihypertensive monotherapy with the angiotensin converting enzyme inhibitor enalapril, but exacerbated by antihypertensive therapy with the dihydropyridine calcium channel blocker amlodipine. These results implicate a potentially important role for the sympathetic nervous system in explaining recent trial data suggesting an added renoprotective effect of antihypertensive agents that block the renin-angiotensin system. Future clinical trials are needed to determine whether normalization of sympathetic activity should constitute an important therapeutic goal to improve renal and cardiovascular outcomes in patients with chronic renal failure.

Congestive heart failure due to systolic dysfunction: the Cinderella of cardiovascular management in dialysis patients

Cardiac disease is common in dialysis patients. Survival is poorest in the subgroup with systolic dysfunction (pump failure). Audits show that cardiovascular management of dialysis patients in general, and treatment of congestive heart failure (CHF) specifically, is generally not in agreement with recommendations based on evidence obtained from controlled trials, admittedly in nonrenal patients. The pathophysiology underlying CHF and the rationale underlying interventions are discussed in an effort to heighten awareness of this important clinical problem in the dialysis community.

Effects of chronic calcium channel blockade on sympathetic nerve activity in hypertension

The sympathetic nervous system (SNS) is an important regulator of the circulation. Its activity is increased in hypertension and heart failure and adversely affects prognosis. Although certain drugs inhibit SNS, dihydropyridine calcium antagonists may stimulate the system. Phenylalkylamine calcium antagonists such as verapamil have a different pharmacological profile. We therefore tested the hypothesis of whether amlodipine, nifedipine, or verapamil differs in the effects on muscle sympathetic nerve activity (MSA). Forty-three patients (31 men, 12 women) with mild to moderate hypertension were randomly assigned to 1 drug for 8 weeks. Blood pressure, heart rate, and MSA (by microneurography) were measured at baseline and after 8 weeks of treatment. All calcium antagonists led to a similar decrease in blood pressure of 5.0+/-1.5 to 6.4+/-1.4 mm Hg at 8 weeks (P<0.001 versus baseline). There were no significant differences in MSA between groups. With amlodipine, MSA averaged 49+/-3 bursts/min (3 versus baseline); with nifedipine, 48+/-3 bursts/min (2 versus baseline); and with verapamil, 49+/-2 bursts/min (all, P=NS). With verapamil, norepinephrine decreased by 4% but tended to increase by about one third with amlodipine or nifedipine (P=NS). Thus, in hypertension slow release forms of verapamil, nifedipine, and amlodipine exert comparable antihypertensive effects and do not change MSA, although there was a trend toward decreased MSA and plasma norepinephrine with verapamil.

Plasma norepinephrine predicts survival and incident cardiovascular events in patients with end-stage renal disease

BACKGROUND

Sympathetic tone is consistently raised in patients with end-stage renal disease (ESRD). We therefore tested the hypothesis that sympathetic activation is associated with mortality and cardiovascular events in a cohort of 228 patients undergoing chronic hemodialysis who did not have congestive heart failure at baseline and who had left ventricular ejection fraction >35%.

METHODS AND RESULTS

The plasma concentration of norepinephrine (NE) was used as a measure of sympathetic activity. Plasma NE exceeded the upper limit of the normal range (cutoff 3.54 nmol/L) in 102 dialysis patients (45%). In a multivariate Cox regression model that included all univariate predictors of death as well as the use of sympathicoplegic agents and beta-blockers, plasma NE proved to be an independent predictor of this outcome (hazard ratio [1-nmol/L increase in plasma NE]: 1.07, 95% CI 1.01 to 1.14, P=0.03). Similarly, plasma NE emerged as an independent predictor of fatal and nonfatal cardiovascular events (hazard ratio [1-nmol/L increase in plasma NE] 1.08, 95% CI 1.02 to 1.15, P=0.01) in a model that included previous cardiovascular events, pulse pressure, age, diabetes, smoking, and use of sympathicoplegic agents and beta-blockers. The adjusted relative risk for cardiovascular complications in patients with plasma NE >75th percentile was 1.92 (95% CI 1.20 to 3.07) times higher than in those below this threshold (P=0.006).

CONCLUSIONS

Sympathetic nerve overactivity is associated with mortality and cardiovascular outcomes in ESRD. Controlled trials with antiadrenergic drugs are needed to determine whether interference with the sympathetic system could reduce the high cardiovascular morbidity and mortality in dialysis patients.

Sympathetic nervous system and the kidney in hypertension

Long-term control of arterial pressure has been attributed to the kidney by virtue of its ability to couple the regulation of blood volume to the maintenance of sodium and water balance by the mechanisms of pressure natriuresis and diuresis. In the presence of a defect in renal excretory function, hypertension arises as the consequence of the need for an increase in arterial pressure to offset the abnormal pressure natriuresis and diuresis mechanisms, and to maintain sodium and water balance. There is growing evidence that an important cause of the defect in renal excretory function in hypertension is an increase in renal sympathetic nerve activity (RSNA). First, increased RSNA is found in animal models of hypertension and hypertensive humans. Second, renal denervation prevents or alleviates hypertension in virtually all animal models of hypertension. Finally, increased RSNA results in reduced renal excretory function by virtue of effects on the renal vasculature, the tubules, and the juxtaglomerular granular cells. The increase in RSNA is of central nervous system origin, with one of the stimuli being the action of angiotensin II, probably of central origin. By acting on brain stem nuclei that are important in the control of peripheral sympathetic vasomotor tone (e.g. rostral ventrolateral medulla), angiotensin II increases the basal level of RSNA and impairs its arterial baroreflex regulation. Therefore, the renal sympathetic nerves may serve as the link between central sympathetic nervous system regulatory sites and the kidney in contributing to the renal excretory defect in the development of hypertension.

Relationship between muscle sympathetic nerve activity and large artery mechanical vessel wall properties in renal transplant patients

OBJECTIVES

Renal transplant recipients (RTX) show a major impairment of large artery elastic wall properties. Sympathetic overactivity present in patients with renal disease has been shown to alter large artery elasticity; however, in RTX, this issue has not been addressed. The present study therefore investigated a possible relationship between sympathetic activity and large artery distensibility in RTX.

METHODS

In 32 patients treated with calcineurin inhibitors (RTX-CI, cyclosporine n = 16, tacrolimus n = 16) mean arterial pressure (MAP, automatic sphygmomanometer), muscle sympathetic nerve activity (MSNA, microneurography) and distensibility coefficients of the brachial and carotid arteries (pulsed Doppler) were measured. Sixteen healthy volunteers (CTR), six patients with calcinneurin inhibitor-free immunosuppression (RTX-AZA) and 12 transplant patients after native kidney nephrectomy (RTX-NC) served as control groups.

RESULTS

RTX-CI significantly increased MSNA compared to CTR (36 +/- 3 versus 16 +/- 2 bursts/min, P < 0.05, mean +/- SEM). Both brachial and carotid artery distensibility were decreased in RTX-CI compared to CTR (7 +/- 1 versus 13 +/- 1 +/- 10(-3) /kPa and 17 +/- 1 versus 25 +/- 2 x 10(-3) /kPa, respectively, both P < 0.05). In RTX-CI, a significant inverse correlation between brachial, but not carotid artery distensibility and MSNA (r = -0.46, P < 0.01, r = -0.12, not significant, respectively) was found. Correlation between brachial artery distensibility and MSNA remained statistically significant on separate analysis of cyclosporine- or tacrolimus-treated RTX and after correction for arterial diameter, blood pressure, graft function, age and sex by stepwise multiple regression analysis. Results in RTX-AZA were similar to those in RTX-CI. In contrast, in RTX-NC with MSNA not significantly different from CON (16.6 +/- 2.0 bursts/min), brachial artery distensibility was significantly higher compared to RTX-CI and RTX-AZA (14.2 +/- 2.0 x 10(-3) /kPa, P < 0.05, respectively).

CONCLUSIONS

Increased sympathetic nerve activity in renal transplant patients is related to decreased distensibility of the muscular type brachial artery, but not the elastic type carotid artery.

Sympathetic activation markedly reduces endothelium-dependent, flow-mediated vasodilation

OBJECTIVES

We sought to evaluate whether increased sympathetic outflow may interfere with flow-mediated dilation (FMD).

BACKGROUND

Endothelial function, assessed as FMD, is frequently used as an intermediate end point in intervention studies. Many disease states with increased sympathetic tone are also characterized by endothelial dysfunction.

METHODS

Sixteen healthy volunteers underwent FMD studies with and without concomitant sympathetic stimulation. Intra-arterial nitroglycerin (NTG) infusion was used to assess endothelium-independent vasodilation. Pathophysiologically relevant sympathetic stimulation was achieved by baroreceptor unloading, using a lower body negative pressure box. In a subset of eight volunteers, this protocol was repeated during loco-regional alpha-adrenergic blockade by intra-arterial infusion of phentolamine (PE). Reactive hyperemic flow was assessed with strain-gauge phlethysmography.

RESULTS

Overall, FMD responses (8.3 +/- 3.4%) were significantly attenuated by concomitant sympathetic stimulation (3.6 +/- 3.4%, p < 0.01). Loco-regional alpha-adrenergic blockade had no effect on baseline FMD responses (10.7 +/- 4.7%), whereas the attenuation by sympathetic stimulation was abolished completely during PE co-infusion (11.5 +/- 3.3%). During intra-arterial NTG infusions, arterial diameters relative to baseline were not significantly different between the four possible stages.

CONCLUSIONS

Sympathetic stimulation, at a clinically relevant range, significantly impairs the FMD response by an alpha-adrenergic mechanism.

Hemodialysis-associated hypertension: pathophysiology and therapy

The majority of end-stage renal disease (ESRD) patients are hypertensive. Hypertension in the hemodialysis patient population is multifactorial. Further, hypertension is associated with an increased risk for left ventricular hypertrophy, coronary artery disease, congestive heart failure, cerebrovascular complications, and mortality. Antihypertensive medications alone do not adequately control blood pressure (BP) in hemodialysis patients. There are, however, several therapeutic options available to normalize BP in these patients, often without the need for additional drug therapy (eg, long, slow hemodialysis; short, daily hemodialysis; nocturnal hemodialysis; or, most effectively, dietary salt and fluid restriction in combination with reduction of dialysate sodium concentration). Optimal BP in dialysis patients is not different from recommendations for the general population, even though definite evidence is not yet available. Predialysis systolic and diastolic BPs are of particular importance. Left ventricular mass correlates with predialysis systolic BP. Survival is better in hemodialysis patients with a mean arterial pressure below 99 mm Hg as compared with those with higher BP. Low predialysis systolic BP (<110 mm Hg) and low predialysis diastolic BP (<70 mm Hg) are associated with increased mortality, primarily because of severe congestive heart failure or coronary artery disease. Patients that experience repeated intradialytic hypotensive episodes should also be viewed with caution, and predialytic BP values should be reevaluated. A possible treatment option for these patients may be slow, long hemodialysis; short, daily hemodialysis; or nocturnal hemodialysis. Among the antihypertensive agents currently available, angiotensin-converting enzyme (ACE) inhibitors appear to have the greatest ability to reduce left ventricular mass. Pressure load can be satisfactorily determined by using the average value of predialysis BP measurements over 1 month. In selected hemodialysis patients, interdialytic ambulatory blood pressure monitoring (ABPM) may help to determine if the patient is in fact hypertensive. In addition, ABPM provides important information about the change in BP between day and night. Regular home BP monitoring, yearly echocardiography, and treatment of traditional risk factors for cardiovascular disease are recommended.

Blood pressure reduction in the morning yields beneficial effects on progression of chronic renal insufficiency with regression of left ventricular hypertrophy

Self-monitoring values of blood pressure may better reflect the average long-term blood pressure value than sporadic measurements in the physician's office and be more useful for blood pressure control. In the present study, we compared the results of self-monitoring of blood pressure values, especially in the morning, with office blood pressure, and related these to progression of chronic renal insufficiency and left ventricular hypertrophy (LVH). Thirty-four patients were selected from 316 subjects with chronic renal insufficiency (average serum creatinine 1.72 +/- 0.15 mg/dl, mean age 52.6 +/- 3.5 yrs) in accordance with the following criteria (1) office blood pressure was less than 140/90 mmHg, (2) blood pressure was controlled with amlodipine (5-20 mg/day) combined with benazepril (2.5 mg/day), (3) morning blood pressure was greater than 150/90 mmHg at 6-9 AM and (4) LVH had been determined by echocardiography (posterior wall thickness; PWT > or = 12 mm). The patients were assigned to 2 groups at random and were given: (1) guanabenz (GB; 2-8 mg at I I PM, n = 17) or (2) placebo (n = 17). Two years later, the average blood pressure of both groups as measured in the office was not significantly different: however, BP in the morning was significantly reduced from 158 +/- 6 to 134 +/- 4 mmHg in GB treated group (P< 0.001). In 14 of 17 patients in GB treated group, LVH resolved and there was only mild progression of nephropathy (serum creatinine: 1.69 +/- 0.18 to 1.81 +/- 0.19 mg/dl). In 12 of 14 patients in placebo group, whose morning blood pressure remained at greater than 150/90 mmHg, LVH was retained and there was moderate progression of nephropathy (serum creatinine: 1.73 +/- 0.14 to 2.62 +/- 0.50mg/dl). From these results, it is suggested that antihypertensive treatment with combination therapy based on self-monitoring BP is cardio-renoprotective in patients with chronic renal insufficiency and LVH.

Sympathetic overactivity as a cause of hypertension in chronic renal failure

OBJECTIVE

To review the current literature on sympathetic mediation of hypertension in chronic renal failure.

BACKGROUND

Hypertension is present in the vast majority of patients with chronic renal failure and constitutes a major risk factor for the excessive cardiovascular morbidity and mortality in this patient population. Although, traditionally, this hypertension is thought to be largely volume-dependent, an increasing body of literature suggests that there is an important sympathetic neural component. Microneurographic studies have demonstrated sympathetic overactivity without baroreflex impairment in both hypertensive chronic hemodialysis patients as well as in those with less advanced renal insufficiency. Sympathetic nerve activity was found to be normal in hemodialysis patients with bilateral nephrectomy, leading to the hypothesis that sympathetic overactivity in uremia is caused by a neurogenic signal (carried by renal afferents) arising in the failing kidney. This hypothesis is supported by rat studies showing that renal deafferentation abrogates hypertension in the 5/6 nephrectomy model of chronic renal insufficiency. In addition, in patients with chronic renal insufficiency and renin-dependent hypertension, sympathetic overactivity was normalized by chronic angiotensin converting enzyme inhibition but not by calcium channel blockade, implicating a major central neural action of angiotensin II.

CONCLUSIONS

Sympathetic overactivity in chronic renal failure is caused by neurohormonal mechanisms arising in the failing kidney. Future clinical studies are needed to determine whether normalization of sympathetic activity should constitute an important therapeutic goal in this high-risk patient population.

Cardiac beta-adrenoceptor desensitization due to increased beta-adrenoceptor kinase activity in chronic uremia

Patients with chronic renal failure develop an autonomic dysfunction with impaired baroreflex control and attenuated cardiovascular beta-adrenoceptor response to noradrenaline. In rats that underwent 5/6-nephrectomy (SNX), cardiac beta-adrenoceptor responsiveness was reduced as well. Therefore, the aim of this study was to further investigate the mechanism underlying cardiac beta-adrenoceptor desensitization in SNX rats. For this purpose, right and left ventricular beta-adrenoceptor density, activity of the G-protein-coupled receptor kinase, and activity and density of the neuronal noradrenaline transporter (uptake1) were assessed in SNX rats. Seven weeks after SNX, rats had developed left heart hypertrophy. Plasma creatinine, urea, and noradrenaline levels were significantly increased; left and right ventricular noradrenaline content was significantly decreased when compared with sham-operated control rats. In these SNX rats, left, but not right, ventricular beta-adrenoceptor density was significantly reduced, and membrane-associated G-protein-coupled receptor kinase activity was significantly increased compared with sham-operated rats. Although right and left ventricular activity of uptake1 was unchanged, the neuronal noradrenaline transporter density was significantly reduced in both ventricles of SNX versus sham-operated rats. An increase in left ventricular G-protein-coupled receptor kinase activity, possibly triggered by enhanced cardiac noradrenaline release, might be responsible for the decrease in left ventricular beta-adrenoceptor responsiveness in SNX rats.

Calcium channel antagonists in the treatment of hypertension

Calcium channel antagonists are widely used antihypertensive agents. Their popularity among primary care physicians is not only due to their blood pressure-lowering effects, but also because they appear to be effective regardless of the age or ethnic background of the patients. The first available calcium channel antagonists utilized immediate-release formulations which, although effective in patients with angina pectoris, were not approved by the US FDA for use in hypertension. When long-acting once-daily formulations were approved in this indication, the short-acting preparations--which had by then become generic and inexpensive--retained some residual unapproved use for hypertension. An observational case-controlled trial, based on such usage, noted that these agents were associated with a greater risk of myocardial infarctions than conventional agents such as diuretics and beta-adrenoceptor antagonists. Further case-controlled trials showed, in fact, that the dangers of calcium channel antagonists were confined to the short-acting agents and that approved long-acting agents were at least as well tolerated and effective as other antihypertensive drugs. Cardiovascular outcomes during treatment with calcium channel antagonists have been examined in randomized, controlled trials. Compared with placebo, the calcium channel antagonists clearly prevented strokes and other cardiovascular events and reduced mortality. The effects of these agents on survival and clinical outcomes were similar to those with other antihypertensive drugs. There is a slight tendency for the calcium channel antagonists to be more effective than other drug types in preventing stroke, but slightly less effective in preventing coronary events. These observations extend to high-risk patients with hypertension including those with diabetes mellitus. Even so, patients with evidence of nephropathy should not receive monotherapy with calcium channel antagonists. Such patients are optimally treated with angiotensin receptor antagonists or ACE inhibitors, although addition of other drugs, including calcium channel antagonists, is often required to achieve the tight blood pressure control necessary to provide adequate renal protection. Calcium channel antagonists have a highly acceptable tolerability profile and careful reviews of available data have shown that their use is not associated with increased bleeding or promotion of tumor formation. It is now recognized that reduction of blood pressure in patients with hypertension to levels often <130/85 mm Hg should be undertaken in presence of other cardiovascular risk factors or evidence of end organ damage. Because of this important concept, calcium channel antagonists, like the other antihypertensive drug classes, are progressively being prescribed less often as monotherapy, but more typically as part of combination regimens.

Contribution of volume overload and angiotensin II to the increased pulse wave velocity of hemodialysis patients

Aortic compliance is decreased in patients with end-stage renal disease. This malfunction contributes to high aortic systolic pressures and thus to the development of left ventricular hypertrophy. It was hypothesized that besides structural vascular changes, functional changes as a result of hypervolemia and increased vasoconstrictor activity, in particular angiotensin II, play a role in decreasing aortic compliance. Nineteen hemodialysis patients were studied before and 24 h after they had been dialyzed to dry weight. Applanation tonometry of peripheral arteries was used to estimate aortic pulse wave velocity (PWV), known to depend on aortic compliance, and aortic systolic pressure augmentation (augmentation index [Aix]). Predialysis aortic PWV was increased in the dialysis patients compared with matched healthy subjects (9.9 +/- 3.1 versus 7.5 +/- 1.1 m/s; P < 0.05). The AIx was also increased (35 +/- 6 versus 25 +/- 10; P < 0.05). Volume reduction with dialysis had no significant effect on PWV (9.3 +/- 1.5 m/s), but the AIx decreased (28 +/- 7; P < 0.05). A subset of 10 patients were restudied after 1 wk of angiotensin-converting enzyme inhibition (ACEi) with enalapril 5 mg once daily. ACEi decreased both predialysis as postdialysis BP but had no effect on pulse pressure and heart rate, which remained elevated compared with healthy subjects. ACEi also decreased predialysis aortic PWV, from 11.0 +/- 3.5 to 9.1 +/- 2.1 m/s (P < 0.05) but had no significant effect on AIx. During treatment with ACEi, the same volume reduction with dialysis decreased aortic PWV further to 8.0 +/- 1.4 m/s (P < 0.05), a figure not different from PWV in healthy subjects. AIx decreased to an even slightly subnormal value (12 +/- 23; P < 0.05). It was concluded that volume overload and angiotensin II both contribute to elevated PWV and AIx in dialysis patients. Volume reduction and ACEi both improve the aortic PWV and AIx. Combined volume reduction and ACEi has an enhanced effect that, in the present patients, was so large that PWV and AIx were no longer elevated. Monitoring and correcting of arterial pressure waves is feasible and may be an important tool in the treatment of patients with end-stage renal disease.

Autonomic tone as a cardiovascular risk factor: the dangers of chronic fight or flight

Chronic imbalance of the autonomic nervous system is a prevalent and potent risk factor for adverse cardiovascular events, including mortality. Although not widely recognized by clinicians, this risk factor is easily assessed by measures such as resting and peak exercise heart rate, heart rate recovery after exercise, and heart rate variability. Any factor that leads to inappropriate activation of the sympathetic nervous system can be expected to have an adverse effect on these measures and thus on patient outcomes, while any factor that augments vagal tone tends to improve outcomes. Insulin resistance, sympathomimetic medications, and negative psychosocial factors all have the potential to affect autonomic function adversely and thus cardiovascular prognosis. Congestive heart failure and hypertension also provide important lessons about the adverse effects of sympathetic predominance, as well as illustrate the benefits of beta-blockers and angiotensin-converting enzyme inhibitors, 2 classes of drugs that reduce adrenergic tone. Other interventions, such as exercise, improve cardiovascular outcomes partially by increasing vagal activity and attenuating sympathetic hyperactivity.

Lisinopril therapy for hemodialysis hypertension: hemodynamic and endocrine responses

To evaluate the antihypertensive effects of lisinopril, a renally excreted angiotensin-converting enzyme inhibitor, we assessed supervised administration of the drug after hemodialysis (HD) three times weekly. Blood pressure (BP) was assessed by interdialytic 44-hour ambulatory BP (ABP) monitoring, and endocrine responses were assessed by plasma renin activity (PRA) before and after dialysis. Lisinopril dose was titrated at biweekly intervals. If this was not effective after full titration (lisinopril to 40 mg three times weekly), ultrafiltration was added to reduce dry weight. The primary outcome variable was change in BP from the end of the run-in period to the end of the study. No change in mean ABP was noted during run-in. However, mean 44-hour ABP decreased from 149 +/- 14 (SD)/84 +/- 9 to 127 +/- 16/73 +/- 9 mm Hg, a decrease of 22/11 mm Hg (P < 0.001) at final evaluation. Of 11 patients who completed the trial, only 2 patients had systolic hypertension (>/=135 mm Hg) and 1 patient had diastolic hypertension (>/=85 mm Hg) at the final visit. Four patients were administered 10 mg of lisinopril; 5 patients, 20 mg; and 2 patients, 40 mg; only 1 of these patients required ultrafiltration therapy. There was a persistent antihypertensive effect over 44 hours. BP reduction was achieved without an increase in intradialytic symptomatic or asymptomatic hypotensive episodes. PRA increased in response to dialysis, as well as lisinopril. In conclusion, supervised lisinopril therapy is effective in controlling hypertension in chronic HD patients. This may be related to blockade of angiotensin II generation by kidneys despite the loss of excretory function.

Hypertension and the kidney

Hypertension and kidney function are intimately related, with each having significant influences on the other. Given the major role played by the kidney in maintenance of extracellular fluid volume and peripheral vascular resistance, the kidney is justifiably a target of investigation to determine its potential role in essential hypertension. Conversely, hypertension is associated with progressive renal failure, and hypertension-associated end-stage renal disease is the second leading cause of end-stage renal disease in the United States. It is therefore important that we continue to investigate the hypertension/renal relationship in an effort to better understand the determinants of essential hypertension and to prevent a major cause of end-stage renal disease.

Sympathetic activity is increased in polycystic kidney disease and is associated with hypertension

Hypertension is common in patients with polycystic kidney disease (PKD). This study addresses the hypothesis that sympathetic activity is enhanced in hypertensive PKD patients, not only when renal function is impaired but also when renal function is still normal. Muscle sympathetic nerve activity (MSNA, peroneal nerve), plasma renin activity (PRA), heart rate, and BP were studied in PKD patients with normal and with impaired renal function and in matched controls. In hypertensive patients with normal renal function, MSNA and mean arterial pressure (MAP) were higher than in normotensive patients (23 +/- 5 versus 15 +/- 7 bursts/min; 110 +/- 10 versus 90 +/- 3 mmHg; P < 0.05), whereas PRA and heart rate did not differ. In PKD with chronic renal failure (CRF) (creatinine clearance rate, 39 +/- 19 ml/min), MAP, MSNA and PRA were higher than in controls (resp, 116 +/- 7 versus 89 +/- 9 mmHg; 34 +/- 14 versus 19 +/- 9 bursts/min; 405 [20 to 1640] versus 120 [40 to 730] fmol/L per sec; all P < 0.05). Heart rate in PKD CRF did not differ from controls. MSNA correlated with MAP (r = 0.42; P = 0.01) and age with MSNA (r = 0.45; P < 0.01). Regression line of age and MSNA in patients was steeper than that in controls. This study indicates that MSNA is increased in hypertensive PKD patients regardless of renal function. The data support the idea that sympathetic hyperactivity contributes to the pathogenesis of hypertension in PKD.

Enalaprilat blunts reflexive increases in cardiac interstitial norepinephrine in conscious rats

OBJECTIVE

We have reported that acute administration of enalaprilat, an angiotensin converting enzyme inhibitor, induces less reflexive increase in lumbar sympathetic nerve activity in spontaneously hypertensive rats (SHRs) than nicardipine, a dihydropyridine calcium-channel blocker. The current study was conducted to determine if angiotensin converting enzyme inhibitors likewise suppress cardiac sympathetic activation.

DESIGN

Cardiac interstitial levels of norepinephrine were measured in fully conscious SHRs before and after acute blood pressure lowering with enalaprilat or nicardipine.

METHODS

Microdialysis probes were inserted into the left ventricular wall of SHRs. Twenty-four to 48 hours post-implantation, myocardial interstitial fluid was collected in fully conscious rats during a 60-min baseline period. Mean arterial pressure was lowered 20 mmHg with intravenous infusion of enalaprilat or nicardipine. During continuous enalaprilat or nicardipine infusion, myocardial interstitial fluid was again collected. Norepinephrine levels were assayed in the perfusate.

CONCLUSIONS

Enalaprilat-induced reduction in mean arterial pressure did not significantly increase cardiac interstitial norepinephrine levels. In contrast, nicardipine-induced reduction in blood pressure was associated with a significant increase in interstitial norepinephrine levels. These results indicate that enalaprilat suppresses reflexive sympathetic activation of the heart during acute blood pressure lowering. These results may be clinically relevant in that reductions in end-organ sympathetic stimulation may enhance the long-term cardiovascular benefit of angiotensin converting enzyme inhibitors.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Glomerulosclerosis and progression: effect of subantihypertensive doses of alpha and beta blockers

BACKGROUND

Uremia is characterized by inadequately increased sympathetic activity. Sympathetic overactivity is involved in the genesis of hypertension in uremia, but its potential role on progression has not been well investigated. To address this issue, the effect of subantihypertensive doses of an alpha blocker and a beta blocker, and their combination on renal morphology and on albuminuria were investigated in the model of the subtotally nephrectomized rat.

METHODS

Male Sprague-Dawley rats were subjected to surgical ablation (SNX) or sham operation (sham). Three days after surgery groups were treated either with phenoxybenzamine (PBZ, 5 mg/kg body weight/day), metoprolol (MET, 150 mg/kg body weight/day) or their combination (PBZ 2.5 mg/kg body weight/day + MET, 50 mg/kg body weight/day). Renal morphology was evaluated after 12 weeks by quantitative histology, immunohistochemistry, and electron microscopy. Urine albumin excretion and kidney endothelin-1 (ET-1), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta) mRNA expression were assessed.

RESULTS

Systolic blood pressure was significantly higher in all SNX groups compared with sham-operated controls with no difference in the SNX groups. The number of glomeruli per left kidney was reduced from 30,904 +/- 3212 to 17,480 +/- 2341 by SNX (-43.5%). Mean glomerular volume increased from 2.63 +/- 0.7 in untreated sham operated to 4.11 +/- 0.48 microm 3 x 10(6) in untreated SNX (56.3%). The glomerulosclerosis index did not change in SNX + PBZ rats, but was significantly lower in SNX + MET (0.56 +/- 0.14) and particularly SNX + PBZ + MET rats (0.49 +/- 0.11) than in untreated SNX (0.74 +/- 0.24). Glomerular capillary length density (LV) as a sensitive index of capillary obliteration was significantly lower in SNX and almost normalized in the three intervention groups. The same was true for the mean podocyte number per glomerulus. Glomerular ultrastructure in SNX was largely preserved by all treatments. The albumin excretion rate was significantly higher in untreated SNX than in sham; it was significantly lower in all treated SNX groups.

CONCLUSION

The beneficial effect of non-hypotensive doses of alpha and beta blockers and their combination on renal morphology and albuminuria in the model of renal ablation argue for a blood pressure-independent role of sympathetic overactivity in the genesis of progression. In addition, the beneficial effect of adrenergic receptor blockade indicates that a substantial part is not mediated by sympathetic cotransmitters such as adenosine 5'-triphosphate (ATP) and neuropeptide Y (NPY).

Therapeutic potential of angiotensin II receptor antagonists

The circulating renin-angiotensin system plays an important role in cardiovascular homeostasis. More importantly, the local tissue renin angiotensin plays a pivotal role in cell growth and remodelling of cardiomyocytes and on the peripheral arterial vasculature. In addition, the renin angiotensin system is related to apoptosis, control of baroreflex and autonomic responses, vascular remodelling and regulation of coagulation, inflammation and oxidation. The cardioprotective and vascular protective effects of the angiotensin receptive blockade appears to be related to selective blockade of the angiotensin II (A-II) Type I (AT(1)) receptors. However, there is now growing evidence showing that some of the effects of AT-II receptor blockers (ARBs) are related to the activation of the kinin pathways. This paper will review some of the recent mechanisms related to the cardiovascular effects of angiotensin and more specifically of ARBs. This paper will present the novel data on the role of ARB in the development of atherosclerosis, vascular remodelling, coagulation balance and autonomic regulation. Finally, the role of ARBs, used alone or in combination with ACE inhibitor in patients with heart failure, will be discussed.

Do most antihypertensive agents have a sympatholytic action?

The sympathetic nervous system is a major modulator of cardiovascular functions. Over the past three decades, numerous studies, using various methodologies, have reported the existence of a variety of pre- and postsynaptic sympathetic dysfunctions in essential hypertension. Most of those abnormalities facilitate sympathetic neurotransmission, resulting in a chronic increase in the sympathetic tone and reactivity in an important proportion of hypertensive patients. The chronic sympathetic activation is also associated with major alterations in the balance between postsynaptic adrenergic receptors in cardiovascular tissues. Indeed, an attenuation of beta-adrenergic functions and a potentiation of alpha1-adrenergic functions have been demonstrated in human cardiovascular tissues, suggesting the development of a sympathetic postsynaptic alpha1 dominance during the development and evolution of hypertension. The chronic activation of the sympathetic system is deleterious and could contribute to the development of most cardiovascular complications associated with hypertension. One of the major aims of antihypertensive therapy should be to attenuate pre- or postsynaptic sympathetic tone. Most antihypertensive drugs have been found to improve either pre- or postsynaptic sympathetic functions in hypertensive patients. At the presynaptic level, the effects of antihypertensive drugs have been found to be more variable. At the postsynaptic level, all currently used antihypertensive drugs have been found to attenuate alpha1-adrenergic functions either by interfering directly with intracellular mechanisms underlying alpha1-adrenergic functions or indirectly by decreasing the release of norepinephrine from peripheral sympathetic nerves.

Central sympathoinhibitory effects of calcium channel blockers

It is generally assumed that the arterial vasodilation induced by inhibition of Ca(2+) influx into vascular smooth muscle cells represents the main mechanism for the hypotensive effect of dihydropyridine calcium channel blockers. Increases in sympathetic tone have been related to activation of the arterial baroreflex by rapid lowering of blood pressure. This review highlights new findings in two areas. First, in animal studies, direct central administration of dihydropyridines such as nifedipine or amlodipine lowers sympathetic nerve activity and thereby blood pressure. Peripheral administration of nifedipine or amlodipine at low rates appears to result in gradual accumulation of drug in the central nervous system, and also causes lowering of sympathetic nerve activity and thereby lowering of blood pressure (rather than by arterial vasodilation). Second, in hypertensive humans treated with long-acting dihydropyridines and presumably little activation of the arterial baroreflex, some studies have demonstrated lowering of sympathetic activity (as assessed by plasma norepinephrine), but others reported increases (as assessed by plasma norepinephrine or microneurography). This sympathoexcitatory response may be due to activation of the renin-angiotensin system, particularly at higher doses.

Transdermal estrogen replacement therapy decreases sympathetic activity in postmenopausal women

BACKGROUND

Menopause heralds a dramatic increase in incident hypertension, suggesting a protective effect of estrogen on blood pressure (BP). In female rats, estrogen has been shown to decrease sympathetic nerve discharge (SND) and BP. SND, however, has not been recorded during estrogen replacement therapy (ERT) in humans. Methods and Results-In 12 normotensive postmenopausal women, we conducted a randomized crossover placebo-controlled study to test whether chronic ERT caused a sustained decrease in SND and BP. Twenty-four-hour ambulatory BP, SND, and arterial baroreflex sensitivity were measured before and after 8 weeks of transdermal estradiol (200 microgram/d), oral conjugated estrogens (0.625 mg/d), or placebo. To test the acute effects of estrogen on SND, additional studies were performed in the same women receiving intravenous conjugated estrogens or sublingual estradiol. After 8 weeks of transdermal ERT, the basal rate of SND decreased by 30% (from 40+/-4 to 27+/-4 bursts per minute, P=0.0001) and ambulatory diastolic BP fell by 5+/-2 mm Hg (P=0.0003). In contrast, SND and BP were unaffected either by 8 weeks of oral ERT or by acute estrogen administration. Neither transdermal nor oral ERT had any effects on baroreflex sensitivity.

CONCLUSIONS

In normotensive postmenopausal women, chronic transdermal ERT decreases SND without augmenting arterial baroreflexes and causes a small but statistically significant decrease in ambulatory BP. Sympathetic inhibition is evident only with chronic rather than acute estrogen administration, implying a genomic mechanism of action. Because the effects of transdermal ERT are larger than those of oral ERT, the route of administration may be an important consideration in optimizing the beneficial effects of ERT on BP and overall cardiovascular health.

Add-on angiotensin receptor blockade with maximized ACE inhibition

BACKGROUND

Prolonged angiotensin-converting enzyme (ACE) inhibitor therapy leads to angiotensin I (Ang I) accumulation, which may "escape" ACE inhibition, generate Ang II, stimulate the Ang II subtype 1 (AT1) receptor, and exert deleterious renal effects in patients with chronic renal diseases. We tested the hypothesis that losartan therapy added to a background of chronic (>3 months) maximal ACE inhibitor therapy (lisinopril 40 mg q.d.) will result in additional Ang II antagonism in patients with proteinuric chronic renal failure with hypertension.

METHODS

Sixteen patients with proteinuric moderately advanced chronic renal failure completed a two-period, crossover, randomized controlled trial. Each period was one month with a two-week washout between periods. In one period, patients received lisinopril 40 mg q.d. along with other antihypertensive therapy, and in the other, losartan 50 mg q.d. was added to the previously mentioned regimen. Hemodynamic measurements included ambulatory blood pressure monitoring (ABP; Spacelabs 90207), glomerular filtration rate (GFR) with iothalamate clearances and cardiac outputs by acetylene helium rebreathing technique. Supine plasma renin activity and plasma aldosterone and 24-hour urine protein were measured in all patients.

RESULTS

Twelve patients had diabetic nephropathy, and four had chronic glomerulonephritis. The mean age (+/- SD) was 53 +/- 9 years. The body mass index was 38 +/- 5.7 kg/m(2), and all except two patients were males. Seated cuff blood pressure was 156 +/- 18/88 +/- 12 mm Hg. The pulse rate was 77 +/- 11 per min, and the cardiac index was 2.9 +/- 0.5 L/min/m(2). Mean log 24-hour protein excretion/g creatinine or overall ABPs did not change. Mean placebo subtracted, losartan-attributable change in protein excretion was +1% (95% CI, -20% to 28%, P = 0.89). Similarly, the change in systolic ambulatory blood pressure (ABP) was 4.6 mm Hg (-5.7 to 14.9, P = 0.95), and diastolic ABP was 1.5 mm Hg (-4.5 to 7.6, P = 0.59). No change was seen in cardiac output. However, there was a mean 14% increase (95% CI, 3 to 26%, P = 0.017) in GFR attributable to losartan therapy. A concomitant fall in plasma renin activity by 32% was seen (95% CI, -15%, - 45%, P = 0.002). No hyperkalemia, hypotension, or acute renal failure occurred in the trial. These results were not attributable to sequence or carryover effects.

CONCLUSIONS

Add-on losartan therapy did not improve proteinuria or ABP over one month of add on therapy. Improvement of GFR and fall in plasma renin activity suggest that renal hemodynamic and endocrine changes are more sensitive measures of AT1 receptor blockade. Whether add-on AT1 receptor blockade causes antiproteinuric effects or long-term renal protection requires larger and longer prospective, randomized controlled trials.

Lowering of microalbuminuria in diabetic patients by a sympathicoplegic agent: novel approach to prevent progression of diabetic nephropathy?

There is convincing evidence for a specific BP-independent effect of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers on albuminuria in glomerular disease. Because progression of glomerular disease is not consistently halted by these agents, there is a need to explore potential renoprotective effects of other drugs. Recent animal work documented that nonhypotensive doses of moxonidine, a sympathicoplegic agent, reduce albuminuria and development of glomerulosclerosis in a BP-independent manner. A randomized, crossover design was used to assess the human relevance of the experimental data in 15 normotensive, nonsmoking type 1 diabetic mellitus patients with good glycemic control (age, 37.3 +/- 6.6 yr; 9 men/6 women; duration of diabetes, 23.6 +/- 5.1 yr) with baseline urinary albumin excretion rates (AER) >20 microg/min in the run-in phase. AER was assessed in overnight timed urine collections. The patients were assigned to a 3-wk placebo and a 3-wk moxonidine (0.2 mg twice a day) period, respectively, in random order. This dose causes modest BP lowering in hypertensive individuals but does not affect BP in normotensive individuals. There was no significant effect on ambulatory BP (mean arterial pressure, 91.8 +/- 7.1 mmHg in the third week of placebo and 91.1 +/- 8.7 mm Hg on moxonidine). There was a significant (P< 0.006) difference of the treatment effects between placebo and moxonidine, respectively, on AER; median AER at the end of the placebo period was 39.8 microg/min (range, 15.9 to 117 microg/min) versus 29.0 (range, 9.03 to 85.8 microg/min) at the end of the moxonidine period. The data document an antialbuminuric effect of nonhypotensive doses of moxonidine. Diminished sympathetic traffic to the kidney is the most plausible explanation for the finding.

Sympathetic nervous system and chronic renal failure

The aim of this work was to review evidence on the role of the sympathetic nervous system (SNS) in chronic renal failure (CRF). Three main points are discussed: 1) SNS and pathogenesis of arterial hypertension; 2) SNS and cardiovascular risk; 3) implication of SNS in arterial hypotension during hemodialysis. Several lines of evidence indicate the presence of a sympathetic hyperactivity in CRF, and its relationship with arterial hypertension. It is suggested that diseased kidneys send afferent nervous signals to central integrative sympathetic nuclei, thus contributing to the development and maintenance of arterial hypertension. The elimination of these impulses with nephrectomy could explain the concomitant reduction of blood pressure. Several experiments confirmed this hypothesis. Regarding SNS and cardiovascular risk, some data suggest that reduced heart rate variability identifies an increased risk for both all causes and sudden death, independently from other recognized risk factors. Symptomatic hypotension is a common problem during hemodialysis treatment, occurring in approximately 20-30% of all hemodialysis sessions and is accompanied by acute withdrawal of sympathetic activity, vasodilation and relative bradicardia. This reflex is thought to be evoked by vigorous contraction of a progressively empty left ventricle, activating cardiac mechanoceptors. This inhibits cardiovascular centers through vagal afferents, and overrides the stimulation by baroreceptor deactivation. Alternative explanations include cerebral ischemia and increased production of nitric oxide, which inhibit central sympathetic activity. It is hoped that therapies aimed at modulating sympathetic nerve activity in patients with CRF will ameliorate their prognosis and quality of life.

Sympathetic nervous system, diabetes, and hypertension

Hypertension is twice as frequent in diabetic patients than in the general population. Its prevalence is higher in Type 2 than in Type 1 diabetes: in the former, the onset of hypertension often precedes the diagnosis of diabetes, whereas, in the latter it is strictly related to the presence of nephropathy. Sympathetic nerve overactivity is crucial in the pathogenesis of hypertension in diabetes. It can be related to the activation of the renin-angiotensin-aldosterone (RAA) system in Type 1 diabetic patients with chronic renal failure, or to a condition of insulin resistance/hyperinsulinemia in Type 2 patients with the metabolic syndrome. In patients with early autonomic neuropathy, vagal impairment can lead to a relative predominance of sympathetic activity in the sympatho-vagal balance. In these patients, the onset of hypertension is frequently preceded by reduced nocturnal dipping. Sympathetic overactivity stimulates RAA activity, promotes sodium reabsorption, and increases heart rate, stroke volume and peripheral vascular resistance, thus inducing hypertension and increasing cardiovascular risk. A number of drugs acting either directly or indirectly on sympathetic activity are available for the treatment of hypertension in diabetic subjects. Opinions on the potential advantages of the metabolic profile of some of these drugs are as yet conflicting.

Role of the sympathetic nervous system in cardiac remodeling in hypertension

The role of the sympathetic nervous system in the settings of cardiac hypertrophy is postulated on the basis of experimental and clinical evidence. Only recently, the intimate mechanisms underlying hypertrophic responses of cardiac cell have been explored. Recent evidence spots the role of adrenergic receptors in the activation of several intracellular pathways of signaling that lead to nuclear responses of myocardiocyte. The molecular structures involved in these pathways may represent novel targets of future therapeutic interventions for cardiac hypertrophy and vascular remodeling in hypertension.

Health outcomes associated with calcium antagonists compared with other first-line antihypertensive therapies: a meta-analysis of randomised controlled trials

BACKGROUND

Several observational studies and individual randomised trials in hypertension have suggested that, compared with other drugs, calcium antagonists may be associated with a higher risk of coronary events, despite similar blood-pressure control. The aim of this meta-analysis was to compare the effects of calcium antagonists and other antihypertensive drugs on major cardiovascular events.

METHODS

We undertook a meta-analysis of trials in hypertension that assessed cardiovascular events and included at least 100 patients, who were randomly assigned intermediate-acting or long-acting calcium antagonists or other antihypertensive drugs and who were followed up for at least 2 years.

FINDINGS

The nine eligible trials included 27,743 participants. Calcium antagonists and other drugs achieved similar control of both systolic and diastolic blood pressure. Compared with patients assigned diuretics, beta-blockers, angiotensin-converting-enzyme inhibitors, or clonidine (n=15,044), those assigned calcium antagonists (n=12,699) had a significantly higher risk of acute myocardial infarction (odds ratio 1.26 [95% CI 1.11-1.43], p=0.0003), congestive heart failure (1.25 [1.07-1.46], p=0.005), and major cardiovascular events (1.10 [1.02-1.18], p=0.018). The treatment differences were within the play of chance for the outcomes of stroke (0.90 [0.80-1.02], p=0.10) and all-cause mortality (1.03 [0.94-1.13], p=0.54).

INTERPRETATION

In randomised controlled trials, the large available database suggests that calcium antagonists are inferior to other types of antihypertensive drugs as first-line agents in reducing the risks of several major complications of hypertension. On the basis of these data, the longer-acting calcium antagonists cannot be recommended as first-line therapy for hypertension.

Differentiated response of the sympathetic nervous system to angiotensin-converting enzyme inhibition in hypertension

Hypertension with renal artery stenosis is associated with both an activated renin-angiotensin system and elevated sympathetic activity. Therefore, in this condition it may be favorable to use a therapeutic modality that does not reflexly increase heart rate, renin secretion, and sympathetic nervous activity. The purpose of the present study was to assess overall, renal, and muscle sympathetic activity after short-term administration of an angiotensin-converting enzyme inhibitor (enalaprilat) and a nonspecific vasodilator (dihydralazine) to hypertensive patients with renal artery stenosis. Forty-eight patients undergoing a clinical investigation for renovascular hypertension were included in the study. An isotope dilution technique for assessing norepinephrine spillover was used to estimate overall and bilateral renal sympathetic nerve activity. In 11 patients simultaneous intraneural recordings of efferent muscle sympathetic nerve activity were performed. Thirty minutes after dihydralazine administration, mean arterial pressure fell by 15%, whereas plasma angiotensin II, muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover increased (P<0.05 for all). In contrast, after enalaprilat administration a fall in arterial pressure similar to that for dihydralazine was followed by decreased angiotensin II levels and unchanged muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover, whereas renal norepinephrine spillover increased by 44% (P<0.05). Acute blood pressure reduction by an angiotensin-converting enzyme inhibitor provokes a differentiated sympathetic response in patients with hypertension and renal artery stenosis, inasmuch that overall and muscle sympathetic reflex activation are blunted, whereas the reflex renal sympathetic response to blood pressure reduction is preserved.

Validity of VO(2 max) in predicting blood volume: implications for the effect of fitness on aging

A multiple regression model was constructed to investigate the premise that blood volume (BV) could be predicted using several anthropometric variables, age, and maximal oxygen uptake (VO(2 max)). To test this hypothesis, age, calculated body surface area (height/weight composite), percent body fat (hydrostatic weight), and VO(2 max) were regressed on to BV using data obtained from 66 normal healthy men. Results from the evaluation of the full model indicated that the most parsimonious result was obtained when age and VO(2 max) were regressed on BV expressed per kilogram body weight. The full model accounted for 52% of the total variance in BV per kilogram body weight. Both age and VO(2 max) were related to BV in the positive direction. Percent body fat contributed <1% to the explained variance in BV when expressed in absolute BV (ml) or as BV per kilogram body weight. When the model was cross validated on 41 new subjects and BV per kilogram body weight was reexpressed as raw BV, the results indicated that the statistical model would be stable under cross validation (e.g., predictive applications) with an accuracy of +/- 1,200 ml at 95% confidence. Our results support the hypothesis that BV is an increasing function of aerobic fitness and to a lesser extent the age of the subject. The results may have implication as to a mechanism by which aerobic fitness and activity may be protective against reduced BV associated with aging.

Effects of low dose sympathetic inhibition on glomerulosclerosis and albuminuria in subtotally nephrectomized rats

ABSTRACT.: A potential role of the sympathetic nervous system in progression of renal failure has received little attention. This study examined whether nonhypotensive doses of moxonidine, an agent that reduces sympathetic activity, affects glomerulosclerosis, urine albumin excretion, and indices of renal handling of norepinephrine (NE) in subtotally nephrectomized (SNX) rats. Sprague Dawley rats were SNX or sham-operated (control). SNX rats were either left untreated or treated with moxonidine in a dose (1.5 mg/kg body wt per d) that did not modify telemetrically monitored 24-h BP. Glomerular and renal morphology were evaluated by quantitative histology, immunohistochemistry, and in situ hybridization. Urine albumin excretion rate was analyzed by enzyme-linked immunosorbent assay, and kidney angiotensin II and NE content were measured using HPLC, (3)H-NE uptake, and release. Body and kidney weight and BP were not significantly different between SNX with or without moxonidine. The glomerulosclerosis index was significantly lower in moxonidine-treated (0.88 +/- 0.09) compared with untreated (1.55 +/- 0.28) SNX rats, as was the index of vascular damage (0.32 +/- 0.14 versus 0.67 +/- 0.16). The number of proliferating cell nuclear antigen-positive glomerular and tubular cells per area was significantly higher in untreated SNX rats than in controls and moxonidine-treated SNX rats. The same was true for urine albumin excretion rate. Renal angiotensin II tissue concentration was not affected by moxonidine. In untreated SNX rats, renal nerve stimulation and exogenous NE induced an increase in isolated kidney perfusion pressure (102 +/- 21 versus 63 +/- 8 mmHg). Renal endogenous NE content was significantly lower in SNX rats than in controls (86 +/- 14 versus 140 +/- 17 pg/mg wet weight). Cortical uptake of [(3)H]-NE was not different, but cortical NE release was significantly higher in SNX rats than in controls. Reduced function of presynaptic inhibitory alpha-adreno-receptors is unlikely because an alpha(2)-adrenoceptor antagonist increased NE release. At subantihypertensive doses, moxonidine ameliorates renal structural and functional damage in SNX animals, possibly through central inhibition of efferent sympathetic nerve traffic. In kidneys of SNX rats, indirect evidence was found for increased activity of a reduced number of nerve fibers.

Plasma renin activity in the emergency department and its independent association with acute myocardial infarction

Elevated plasma renin activity (PRA) is associated with increased risk of future myocardial infarction (MI) in ambulatory hypertensive patients. The present study evaluated the relationship of PRA to the diagnosis of acute MI in patients presenting to an emergency department with suspected acute MI. PRA was measured upon entry to the emergency department, before any acute treatment, as part of the standard evaluation of 349 consecutive patients who were hospitalized for suspected MI. Diagnosis of acute MI was confirmed in 73 patients, and ruled out in 276. They did not differ in age (65.9 +/- 2 v 66.1 +/- 1 years), systolic (143 +/- 4 v 140 +/- 2 mm Hg), or diastolic (81 +/- 2 v 81 +/- 1 mm Hg) pressures. Median PRA was 2.7-fold higher in acute MI (0.89 v 0.33 ng/L/s; P < .001). In a multivariate analysis controlling for other cardiac risk factors and prior drug therapy, PRA as a continuous variable was the predominant independent factor associated with acute MI (P < .0001), followed by white race (P = .002) and history of hypertension (P = .047). The height of the PRA level upon entry to the emergency department was directly and independently associated with the diagnosis of acute MI. These new findings extend earlier reports because they encompass acute MI patients, include both hypertensive and normotensive patients, and control for potentially confounding variables. Based on these observations, a randomized clinical trial is warranted to determine whether measurement of PRA in acute MI could refine the process by which treatments are applied.

Role of the sympathetic nervous system in human renovascular hypertension

The findings in humans as to whether elevated sympathetic nerve activity contributes to renovascular hypertension have been less consistent compared with the results obtained in experimental models of renovascular hypertension. Collectively, there are several lines of evidence to support the view that sympathetic nerve activity is elevated in patients with renovascular hypertension. It is uncertain, however, whether this adrenergic overactivity is specific for renovascular hypertension per se, or the cause of severe hypertension with target organ damage. Central or peripheral stimulation of sympathetic nerve activity by angiotensin II, or stimulation of central sympathetic outflow via afferent renal nerves of ischemic kidneys, are possible mechanisms to explain the elevated sympathetic nerve activity in renovascular hypertension. Therapy that diminishes the activity of the sympathetic nervous system and the renin-angiotensin system seems rational and could perhaps also improve the poor prognosis for these patients.

Cocaine and the kidney: a synthesis of pathophysiologic and clinical perspectives

Cocaine abuse has reached epidemic proportions in the United States, and several forms of renal disease have been associated with this widespread use. The hemodynamic actions of cocaine, as well as its effects on matrix synthesis, glomerular inflammation, and glomerulosclerosis, may contribute to renal injury. Cocaine abuse has been associated with various forms of acute renal failure and acid-base and/or electrolyte disorders and may also have a role in the progression of chronic renal failure to end-stage renal disease. In utero exposure to cocaine has been associated with urogenital tract anomalies. Medical management of a hypertensive emergency caused by acute cocaine toxicity requires a multisystem approach, with close monitoring of cardiac, neurological, and renal functions.

Regulatory peptides and their antagonists in nephropathies

Many peptides influence renal function and structure in physiological and pathophysiological situations. Bioactive peptides that regulate renal function and structure encompass various substances including vasopeptides, growth factors, cytokines and peptide hormones. We highlight some novel concepts indicating that the vasoactive peptides angiotensin II and endothelin-1 play a major role in the progression of renal disease. These effects may be amplified by reduced concentration of counteracting natriuretic peptides. In addition, recent evidence suggests that peptides such as leptin, previously not considered to exert any renal effects, may be involved in renal pathophysiology under certain conditions. One of the most imperative tasks in nephrology is to develop innovative strategies to slow the progression of chronic renal disease. Interference with the renal action of bioactive peptides will certainly be part of this strategy.

The effects of an angiotensin-converting enzyme inhibitor and an angiotensin II receptor antagonist on insulin resistance in fructose-fed rats

The aim of this study was to compare the effects of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor (AT) antagonist on insulin resistance, especially on muscle fiber composition in fructose-induced insulin-resistant and hypertensive rats. Six-week-old male Sprague-Dawley rats were fed either normal rat chow (control) or a fructose-rich diet (FFR). For the last two weeks of a six-week period of either diet, the rats were treated with gum arabic solution as a vehicle (control or FFR), angiotensin-converting enzyme inhibitor (FFR+ACE), temocapril (1 mg/kg/ day) or an angiotensin II receptor antagonist (FFR+AT), CS-866 (0.3 mg/kg/day), by gavage, and then the euglycemic hyperinsulinemic glucose clamp technique was performed to evaluate insulin sensitivity. At the end of the glucose clamp, the soleus muscle was dissected for determination of the muscle fiber composition by ATPase methods. Blood pressure at the glucose clamp in the FFR group was significantly higher than that of the control group, and both temocapril and CS-866 significantly lowered the blood pressure of the FFR group. The average rate of glucose infusion during the glucose clamp, as a measure of insulin sensitivity (M value), was significantly lower in the FFR rats compared to the controls (15.4 +/- 0.4, 10.9 +/- 0.6 mg/kg/min, for control and FFR, respectively, P < .01). Both temocapril and CS-866 partially improved the M values compared to FFR (13.2 +/- 0.7, 12.8 +/- 0.5 mg/kg/min, for FFR+ACE, FFR+AT, respectively, P < .01 compared with FFR, P < .05 compared with control). The composite ratio of type I fibers of the soleus muscle was decreased significantly in the FFR rats compared with the controls (82% +/- 2%, 75% +/- 2%, for control and FFR, respectively, P < .01), and both temocapril and CS-866 restored a composite ratio of type I fibers to the same level as that of the controls (81% +/- 1%, 80% +/- 1% for FFR+ACE and FFR+AT, respectively). The M value was significantly correlated with the composition of type I and type II fibers. These results suggest that the fiber composition of skeletal muscle is correlated to insulin resistance, and that both ACE inhibitors and AT antagonists may modulate the muscle fiber composition in a hypertensive and insulin-resistant animal model, fructose-fed rats, to the same extent.