Renal vasodilatory effect of endothelial stimulation in patients with chronic congestive heart failure

Interventions for renal artery stenosis: Appraisal of novel physiological insights and procedural techniques to improve clinical outcome

Randomized clinical trials failed to show additional benefit of renal artery stenting on top of medical therapy. Instead of writing an obituary on renal artery stenting, we try to explain these disappointing results. A transstenotic pressure gradient is needed to reduce renal perfusion and to activate the renin-angiotensin-aldosterone system. In only a minority of patients included in trials, a transstenotic pressure gradient is measured and reported. Like the coronary circulation, integration of physiological lesion assessment will allow to avoid stenting of non-significant lesions and select those patients that are most likely to benefit from renal artery stenting. Renal artery interventions are associated with peri-procedural complications. Contemporary techniques, including radial artery access, no-touch technique to engage the renal ostium and the use of embolic protection devices, will minimize procedural risk. Combining optimal patient selection and meticulous technique might lead to a netto clinical benefit when renal artery stenting is added to optimal medical therapy.

Endothelial Dysfunction and Heart Failure with Preserved Ejection Fraction-An Updated Review of the Literature

Heart failure (HF) is a clinical syndrome consisting of typical symptoms and signs due to structural and/or functional abnormalities of the heart, resulting in elevated intracardiac pressures and/or inadequate cardiac output. The vascular system plays a crucial role in the development and progression of HF regardless of ejection fraction, with endothelial dysfunction (ED) as one of the principal features of HF. The main ED manifestations (i.e., impaired endothelium-dependent vasodilation, increased oxidative stress, chronic inflammation, leukocyte adhesion, and endothelial cell senescence) affect the systemic and pulmonary haemodynamic and the renal and coronary circulation. The present review is aimed to discuss the contribution of ED to HF pathophysiology-in particular, HF with preserved ejection fraction-ED role in HF patients, and the possible effects of pharmacological and non-pharmacological approaches. For this purpose, relevant data from a literature search (PubMed, Scopus, EMBASE, and Medline) were reviewed. As a result, ED, assessed via venous occlusion plethysmography or flow-mediated dilation, was shown to be independently associated with poor outcomes in HF patients (e.g., mortality, cardiovascular events, and hospitalization due to worsening HF). In addition, SGLT2 inhibitors, endothelin antagonists, endothelial nitric oxide synthase cofactors, antioxidants, and exercise training were shown to positively modulate ED in HF. Despite the need for future research to better clarify the role of the vascular endothelium in HF, ED represents an interesting and promising potential therapeutic target.

Insulin receptors in the kidneys in health and disease

Insulin is an important hormone that affects various metabolic processes, including kidney function. Impairment in insulin’s action leads to insulin resistance in the target tissue. Besides defects in post-receptor insulin signaling, impairment at the receptor level could significantly affect insulin sensitivity of the target tissue. The kidney is a known target of insulin; however, whether the kidney develops “insulin resistance” is debatable. Regulation of the insulin receptor (IR) expression and its function is very well studied in major metabolic tissues like liver, skeletal muscles, and adipose tissue. The physiological relevance of IRs in the kidney has recently begun to be clarified. The credit goes to studies that showed a wide distribution of IR throughout the nephron segments and their reduced expression in the insulin resistance state. Moreover, altered renal and systemic metabolism observed in mice with targeted deletion of the IR from various epithelial cells of the kidney has strengthened this proposition. In this review, we recapitulate the crucial findings from literature that have expanded our knowledge regarding the significance of the renal IR in normal- and insulin-resistance states.

A non-invasive magnetic resonance imaging approach for assessment of real-time microcirculation dynamics

We present a novel, non-invasive magnetic resonance imaging (MRI) technique to assess real-time dynamic vasomodulation of the microvascular bed. Unlike existing perfusion imaging techniques, our method is sensitive only to blood volume and not flow velocity. Using graded gas challenges and a long-life, blood-pool T₁-reducing agent gadofosveset, we can sensitively assess microvascular volume response in the liver, kidney cortex, and paraspinal muscle to vasoactive stimuli (i.e. hypercapnia, hypoxia, and hypercapnic hypoxia). Healthy adult rats were imaged on a 3 Tesla scanner and cycled through 10-minute gas intervals to elicit vasoconstriction followed by vasodilatation. Quantitative T₁ relaxation time mapping was performed dynamically; heart rate and blood oxygen saturation were continuously monitored. Laser Doppler perfusion measurements confirmed MRI findings: dynamic changes in T₁ corresponded with perfusion changes to graded gas challenges. Our new technique uncovered differential microvascular response to gas stimuli in different organs: for example, mild hypercapnia vasodilates the kidney cortex but constricts muscle vasculature. Finally, we present a gas challenge protocol that produces a consistent vasoactive response and can be used to assess vasomodulatory capacity. Our imaging approach to monitor real-time vasomodulation may be extended to other imaging modalities and is valuable for investigating diseases where microvascular health is compromised.

Intravenous Nitroglycerin in the Treatment of Decompensated Heart Failure: Potential Benefits and Limitations

Acute decompensated heart failure (ADHF) is a common cause of hospitalizations. Intravenous nitroglycerin is widely used in the treatment of this condition. The use of this drug is based on its nitric oxide-mediated vasodilatory effect, which can lead to beneficial hemodynamic effects as well as improvement of myocardial ischemia and reduction of mitral regurgitation. However, information regarding the use of nitroglycerin for ADHF is limited to mostly hemodynamic evaluations in small groups of patients without cardiovascular outcome data. A single randomized, placebo controlled study that evaluated commonly used doses of nitroglycerin in patients with ADHF was disappointing and failed to show a significant hemodynamic effect or improvement of symptoms compared with placebo. The potential benefit of nitroglycerin seems to be limited by a decreased vasodilatory response in patients with heart failure, which requires an active titration of the drug and the use of high doses (>120 µg/min). In addition, the initial beneficial hemodynamic effect achieved with the appropriate dose of nitroglycerin is associated with neurohumoral activation and limited by an early development of nitrate tolerance that leads to a marked attenuation of the initial effect. More information obtained in large-scale studies that are appropriately designed to evaluate the effect of variable doses of nitroglycerin on short- and long-term cardiovascular outcome, with and without interventions shown to prevent nitrate tolerance, is needed before intravenous nitroglycerin can be recommended as a standard therapy for ADHF.

Insulin regulates nitric oxide production in the kidney collecting duct cells

The kidney is an important organ for arterial blood pressure (BP) maintenance. Reduced NO generation in the kidney is associated with hypertension in insulin resistance. NO is a critical regulator of vascular tone; however, whether insulin regulates NO production in the renal inner medullary collecting duct (IMCD), the segment with the greatest enzymatic activity for NO production in kidney, is not clear. Using an NO-sensitive 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) fluorescent dye, we found that insulin increased NO production in mouse IMCD cells (mIMCD) in a time- and dose-dependent manner. A concomitant dose-dependent increase in the NO metabolite (NOx) was also observed in the medium from insulin-stimulated cells. NO production peaked in mIMCD cells at a dose of 100 nm insulin with simultaneously increased NOx levels in the medium. At this dose, insulin significantly increased p-eNOS(Ser1177) levels in mIMCD cells. Pretreatment of cells with a PI 3-kinase inhibitor or insulin receptor silencing with RNA interference abolished these effects of insulin, whereas insulin-like growth factor-1 receptor (IGF-1R) silencing had no effect. We also showed that chronic insulin infusion to normal C57BL/6J mice resulted in increased endothelial NOS (eNOS) protein levels and NO production in the inner medulla. However, insulin-infused IRKO mice, with targeted deletion of insulin receptor from tubule epithelial cells of the kidney, had ∼50% reduced eNOS protein levels in their inner medulla along with a significant rise in BP relative to WT littermates. We have previously reported increased baseline BP and reduced urine NOx in IRKO mice. Thus, reduced insulin receptor signaling in IMCD could contribute to hypertension in the insulin-resistant state.

Response of various conduit arteries in tachycardia- and volume overload-induced heart failure

Although hemodynamics changes occur in heart failure (HF) and generally influence vascular function, it is not clear whether various HF models will affect the conduit vessels differentially or whether local hemodynamic forces or systemic factors are more important determinants of vascular response in HF. Here, we studied the hemodynamic changes in tachycardia or volume-overload HF swine model (created by either high rate pacing or distal abdominal aortic-vena cava fistula, respectively) on carotid, femoral, and renal arteries function and molecular expression. The ejection fraction was reduced by 50% or 30% in tachycardia or volume-overload model in four weeks, respectively. The LV end diastolic volume was increased from 65 ± 22 to 115 ± 78 ml in tachycardia and 67 ± 19 to 148 ± 68 ml in volume-overload model. Flow reversal was observed in diastolic phase in carotid artery of both models and femoral artery in volume-overload model. The endothelial function was also significantly impaired in carotid and renal arteries of tachycardia and volume-overload animals. The endothelial dysfunction was observed in femoral artery of volume-overload animals but not tachycardia animals. The adrenergic receptor-dependent contractility decreased in carotid and femoral arteries of tachycardia animals. The protein expressions of NADPH oxidase subunits increased in the three arteries and both animal models while expression of MnSOD decreased in carotid artery of tachycardia and volume-overload model. In conclusion, different HF models lead to variable arterial hemodynamic changes but similar vascular and molecular expression changes that reflect the role of both local hemodynamics as well as systemic changes in HF.

M-atrial natriuretic peptide and nitroglycerin in a canine model of experimental acute hypertensive heart failure: differential actions of 2 cGMP activating therapeutics

Background

Systemic hypertension is a common characteristic in acute heart failure (HF). This increasingly recognized phenotype is commonly associated with renal dysfunction and there is an unmet need for renal enhancing therapies. In a canine model of HF and acute vasoconstrictive hypertension we characterized and compared the cardiorenal actions of M‐atrial natriuretic peptide (M‐ANP), a novel particulate guanylyl cyclase (pGC) activator, and nitroglycerin, a soluble guanylyl cyclase (sGC) activator.

Methods and Results

HF was induced by rapid RV pacing (180 beats per minute) for 10 days. On day 11, hypertension was induced by continuous angiotensin II infusion. We characterized the cardiorenal and humoral actions prior to, during, and following intravenous M‐ANP (n=7), nitroglycerin (n=7), and vehicle (n=7) infusion. Mean arterial pressure (MAP) was reduced by M‐ANP (139±4 to 118±3 mm Hg, P<0.05) and nitroglycerin (137±3 to 116±4 mm Hg, P<0.05); similar findings were recorded for pulmonary wedge pressure (PCWP) with M‐ANP (12±2 to 6±2 mm Hg, P<0.05) and nitroglycerin (12±1 to 6±1 mm Hg, P<0.05). M‐ANP enhanced renal function with significant increases (P<0.05) in glomerular filtration rate (38±4 to 53±5 mL/min), renal blood flow (132±18 to 236±23 mL/min), and natriuresis (11±4 to 689±37 mEq/min) and also inhibited aldosterone activation (32±3 to 23±2 ng/dL, P<0.05), whereas nitroglycerin had no significant (P>0.05) effects on these renal parameters or aldosterone activation.

Conclusions

Our results advance the differential cardiorenal actions of pGC (M‐ANP) and sGC (nitroglycerin) mediated cGMP activation. These distinct renal and aldosterone modulating actions make M‐ANP an attractive therapeutic for HF with concomitant hypertension, where renal protection is a key therapeutic goal.

Renal and hormonal effects of systemic nitric oxide inhibition in patients with congestive heart failure and in healthy control subjects

BACKGROUND

The significance of basal renal nitric oxide (NO) availability in the regulation of renal perfusion and sodium excretion in human congestive heart failure (CHF) has not been described previously.

METHODS AND RESULTS

We studied the effects of acute systemic NO synthesis inhibition with N(G)-monomethyl-L-arginine (L-NMMA) in 12 patients with CHF and 10 healthy control subjects (CON) in a randomized placebo-controlled study. Effect parameters were renal plasma flow (RPF), renal vascular resistance (RVR), glomerular filtration rate (GFR), urine sodium excretion and plasma levels of vasoactive hormones. L-NMMA was associated with a significant decrease in RPF (CON-LNMMA: -13 ± 3% [P = .014]; CHF-LNMMA: -17 ± 7% [P = .017]) and a profound increase in RVR in both CHF and CON (CON-LNMMA: +26 ± 6% [P = .009]; CHF-LNMMA: +37 ± 70% [P = .005]). Significant decreases in sodium excretion were found in both CHF-LNMMA and CON-LNMMA. Relative changes from baseline were not statistically different between CHF-LNMMA and CON-LNMMA. After L-NMMA, RPF values correlated inversely with plasma aldosterone in CHF-LNMMA (P = .01). L-NMMA induced an increase in A-type natriuretic peptide (ANP) only in CHF-LNMMA (+18 ± 8%; P = .035), which correlated significantly with basal ANP levels (P = .034).

CONCLUSIONS

There was no difference in the renal response to L-NMMA in CHF vs CON, suggesting that the impact of NO on renal perfusion and sodium excretion is maintained in stable CHF. We suggest that NO influences the release of ANP during high levels of atrial stretch in CHF.

Can we prevent or treat renal dysfunction in acute heart failure?

Most patients with heart failure (HF) already have or develop renal dysfunction; this might contribute to their poor outcome. Current treatment for HF can also contribute to worsen renal function. High furosemide doses are traditionally associated with worsening renal function (WRF), but patients with fluid overload may benefit of aggressive fluid removal. Unfortunately, promising therapies like vasopressin antagonists and adenosine antagonists have not been demonstrated to improve outcomes. Likewise, correction of low renal blood flow through dopamine, inotropic agents, or vasodilators does not seem to be associated with a clear benefit. However, transient WRF associated with acute HF treatment may not necessarily portend a poor prognosis. In this review, we focus on the strategies to detect renal dysfunction in acute HF, the underlying pathophysiological mechanisms, and the potential treatments.

Vasodilators in the management of acute heart failure

Recent guidelines by the Heart Failure Society of America have recommended consideration for use of nitroprusside, nitroglycerin, or nesiritide in addition to diuretics to achieve hemodynamic and symptomatic improvement. This article reviews the results of previous studies evaluating the pharmacologic and clinical effects and safety profiles of these drugs in patients with heart failure.

Usefulness of translesional pressure gradient and pharmacological provocation for the assessment of intermediate renal artery disease

OBJECTIVE

We sought to determine the hemodynamic significance of intermediate RAS by measuring translesional systolic pressure gradients (TSPG), using a pressure-sensing guidewire at baseline and after acetylcholine (ACh) induced hyperemia, following selective renal artery angiography.

BACKGROUND

Renal artery stenosis (RAS) is a cause of reversible hypertension and nephropathy. Stenting effectively relieves RAS, however improvement in blood pressure control or renal function is variable and unpredictable. Hemodynamic significance is usually present with RAS when diameter stenosis is >75%, but is less predictable in intermediate (30%-75%) RAS.

METHODS

Twenty-two patients (26 renal arteries) with uncontrolled hypertension underwent invasive hemodynamic assessment because of intermediate RAS, defined as radiocontrast angiographic diameter stenosis (DS) between 30% and 75% (quantitative DS was measured prospectively). Translesional pressure gradients were measured using a 0.014" pressure-sensing wire. Hyperemia was induced by administration of intrarenal ACh.

RESULTS

Visual and measured angiographic lesion severity did not correlate with TSPG either at baseline (visual DS, R(2) = 0.091, P = 0.13; measured DS, R(2) = 0.124, P = 0.07) or with hyperemia (visual DS, R(2) = 0.057, P = 0.24; measured DS, R(2) = 0.101, P = 0.12). Baseline and maximal hyperemic gradient did correlate (R(2) = 0.567; P < 0.05). Pharmacological provocation produced a significant increase in TSPG (mean; baseline, 18 +/- 21 vs. hyperemia, 34 +/- 41 mm Hg; P < 0.05). A hemodynamically significant lesion (TSPG > 20 mm Hg) was found in 14/26 (54%) arteries (13 patients); 13 (60%) patients subsequently underwent renal artery stenting for hemodynamically significant RAS. At follow-up (at least 30 days), there was a significant decrease in systolic blood pressure (mean; 167 +/- 24 vs. 134 +/- 19 mm Hg; P < 0.001).

CONCLUSIONS

Intrarenal administration of ACh induces hyperemia and can be used to unmask resistive renal artery lesions. Gradient measurement and induced hyperemia may be warranted in the invasive assessment of intermediate renal artery stenoses, rather than relying on stenosis severity alone. Further study is needed to determine whether translesional pressure gradients and pharmacological provocation predict clinical benefit after renal artery stenting.

Inflammation and endothelial dysfunction as therapeutic targets in patients with heart failure

Evidence suggests that vascular endothelium plays key role in the regulation of vascular tone, in the process of inflammation and in the thrombotic mechanisms. Recent studies indicate that it is an important component of the pathophysiological mechanisms of heart failure. Heart failure may induce endothelial dysfunction by different mechanisms, such as reduced synthesis and release of nitric oxide (NO), increased degradation of NO or by increased production of endothelin-1. In addition, endothelial dysfunction has been associated with the progression of heart failure. Alterations in neurotransmitters, hormones and also in physiological stimuli are present in heart failure and affect the vascular endothelium. Treatments with beneficial effects on endothelial dysfunction may also improve prognosis in patients with heart failure.

Effects of clopidogrel and aspirin combination versus aspirin alone on platelet aggregation and major receptor expression in patients with heart failure: the Plavix Use for Treatment Of Congestive Heart Failure (PLUTO-CHF) trial

BACKGROUND

Persistent platelet activation may contribute to thrombotic events in patients with congestive heart failure (CHF). Chronic use of mild platelet inhibitors could therefore represent an independent avenue to improve morbidity, mortality, and quality of life in this expanding population. Although clopidogrel is widely used in patients with acute coronary syndromes and ischemic stroke, the ability of this novel ADP-receptor antagonist to inhibit platelet function in patients with CHF is unknown. We assessed antiplatelet properties of clopidogrel with aspirin (C+A) versus aspirin alone (A) in patients with CHF with heightened platelet activity.

METHODS

Patients with left ventricular ejection fraction <40%, or CHF symptoms in the setting of preserved systolic function and New York Heart Association class II-IV were screened. Patients were considered to have platelet activation when 4 of the following 5 parameters were met: ADP-induced platelet aggregation >60%; collagen-induced aggregation >70%; whole blood aggregation >18 ohms; expression of GP IIb/IIIa >220 log MFI; and P-selectin cell positivity >8%. All patients were treated with 325 mg of acetylsalycilic acid (ASA) for at least 1 month. Patients receiving an antithrombotic agent other than ASA were excluded. Patients meeting clinical and laboratory criteria were randomly assigned to C+A (n=25), A (n=25) groups, or represent screen failures (n=38). Platelet studies (conventional and whole blood aggregometry, shear-induced activation, expression of 10 major receptors and formation of platelet-leukocyte microparticles) were performed at baseline and after 30 days of therapy.

RESULTS

There were no deaths, hospitalizations, or serious adverse events. There were no changes in platelet parameters in the A group. In contrast, therapy with C+A resulted in a significant inhibition of platelet activity assessed by ADP-induced (P =.00001), and epinephrine-induced (P =.0016) aggregation, closure time (P =.04), expression of PECAM-1 (P =.009), GP Ib (P =.006), GP IIb/IIIa antigen (P =.0001), GP IIb/IIIa activity with PAC-1 (P =.0021), and CD151 (P =.0026) when compared with the A group. Therapy with C+A also resulted in the reduced formation of platelet-leukocyte microparticles (P =.021). Collagen-induced aggregation in plasma and in whole blood, expression of vitronectin receptor, P-selectin, CD63, CD107a, and CD107b did not differ among groups.

CONCLUSIONS

Treatment with C+A for 1 month provides significantly greater inhibition of platelet activity than ASA alone in patients with CHF. Patients with CHF with heightened platelet activity represent a potential target population in which addition of clopidogrel may decrease mortality rates by reducing the incidence of thrombotic vascular events.

Impaired endothelium-mediated vasodilation in heart failure: clinical evidence and the potential for therapy

Numerous studies in the last decade have clearly shown an attenuated endothelium-dependent vasodilation in patients with chronic heart failure. This abnormality has been demonstrated in the peripheral, pulmonary, and coronary circulation in patients with both ischemic and nonischemic cardiomyopathy; its magnitude correlates with the severity of symptoms. Endothelial dysfunction in patients with cardiomyopathy and a relatively new onset of symptoms suggests that change in endothelial function occurs early in the course of the disease. In contrast to other circulatory beds, renal circulation has shown significant vasodilatory response to endothelial stimulation. The development of endothelial dysfunction may not be homogeneous, and its magnitude may differ among circulatory systems. Although the clinical implications of the attenuated endothelium-dependent vasodilation in heart failure are not clear, this condition may lead to decreased organ perfusion, impaired exercise tolerance, and progression of disease. Many therapeutic interventions have resulted in improvement of endothelial function in patients with heart failure. Some of these interventions have also proven effective in enhancing exercise capacity, symptoms, and survival in patients with heart failure. This association suggests a therapeutic role for improvement of endothelial function in patients with chronic heart failure.

Endothelial function in patients with chronic heart failure

Congestive heart failure is characteristically associated with systemic vasoconstriction and impaired vasodilatory capacity, leading to decreased peripheral perfusion. Factors identified as possible causes of reduced vasodilatory capacity include activation of the sympathetic nervous system and the renin-angiotensin system, vascular stiffness due to increased sodium and fluid retention, and structural vascular changes. More recently, the role of the endothelium as a mediator of vasoregulation and tissue perfusion has been recognized.

Functional assessment of the circulation of the single kidney

Functional alterations in the renal circulation that can contribute to abnormal renal perfusion have been demonstrated in various models of renal injury. To detect impairments in renal vascular function, renal flow reserve can be determined by repeated measurements of renal blood flow (RBF) during pharmacological challenge with short-acting vasodilators that should increase RBF in kidneys that are not severely damaged structurally. Among the invasive techniques for such measurements, the most readily available is probably the intravascular Doppler, which can be employed during renal angiography for rapid evaluation of changes in RBF during intrarenal injections of vasoactive substances. High-resolution tomographic imaging techniques, like electron-beam x-ray computed tomography, further offer the potential for noninvasive measurements of renal parenchymal perfusion and function, in association with either intrarenal or systemic injections of vasoactive substances. Acetylcholine is a potent short-acting renal vasodilator that can be useful to assess the response of the renal microcirculation, define renal flow reserve, and examine the endothelium-dependent responses of RBF. Such assessments of the function of the renal circulation can assist in evaluation of patients with systemic or renal disease for early detection and monitoring of renovascular injury.

Abnormal renal vasodilation to an amino acid infusion in congestive heart failure: normalization by enalapril

In congestive heart failure (CHF), the neurohormonal mechanisms that cause renal vasoconstriction, particularly those depending on the renin-angiotensin system, could interfere with renal vasodilating mechanisms. To elucidate this issue, we studied the kidney response to an amino acid infusion (known to cause renal vasodilation in healthy individuals) in eight patients with CHF. We found that the amino acid infusion (0.7 mL/kg/h of a 10% solution) elicited no renal hemodynamic response, in marked contrast to healthy subjects. We next hypothesized that the renin-angiotensin system (known to be activated in heart failure) has a role in the lack of response to the amino acid infusion. To test this hypothesis, we repeated the study after two 5-mg doses of enalapril, an inhibitor of the angiotensin-converting enzyme, administered 12 hours apart. After enalapril treatment, the amino acid infusion caused a 45% increase in mean renal blood flow (RBF) from 383 +/- 55 to 557 +/- 51 mL/min at the fifth hour (P < 0.05). This normalization of the renal response to the amino acid infusion occurred without changes in cardiac output or in systemic vascular resistance. Hence, the renal fraction of the cardiac output increased during the amino acid infusion. The recovery of the renal vascular response was not accompanied by an increase in glomerular filtration rate (GFR; filtration fraction decreased), suggesting a predominant efferent arteriole dilatation. Our study shows that, in heart failure, the kidney loses its ability to increase RBF in response to an amino acid load. This lack of renal vascular response can be restored by inhibiting the renin-angiotensin system and is unrelated to changes in systemic hemodynamics.

Suppressed impact of nitric oxide on renal arteriolar function in rats with chronic heart failure

We performed experiments to test the hypothesis that experimental heart failure (HF) is associated with altered nitric oxide (NO)-dependent influences on the renal microvasculature, including diminished modulation of constrictor responses to ANG II. Eight to ten weeks after inducing HF in rats by coronary artery ligation, we administered enalaprilat to suppress ANG II synthesis and studied renal arteriolar function using the in vitro blood-perfused juxtamedullary nephron technique. In kidneys from sham-operated rats, NO synthase inhibition [100 microM Nomega-nitro-L-arginine (L-NNA)] reduced afferent arteriolar diameter by 4.1 +/- 0.6 microm and enhanced ANG II responsiveness (10 nM ANG II decreased afferent diameter by 10.1 +/- 1.4 micrometer before and 12.8 +/- 1.6 micrometer during L-NNA treatment; P < 0.05). In kidneys from HF rats, L-NNA did not alter afferent arteriolar baseline diameter or ANG II responsiveness (10 nM ANG II decreased diameter by 12.5 +/- 1.5 micrometer before and 12.5 +/- 2.3 micrometer during L-NNA). The effects of L-NNA on efferent arteriolar function were also abated in HF rats. In renal cortex of HF rats, NO synthase activity was decreased by 63% and superoxide dismutase activity was diminished by 39% relative to tissue from sham-operated rats. Urinary nitrate/nitrite excretion was also reduced in HF rats. Thus both diminished synthesis and augmented degradation are likely to contribute to a decreased renal microvascular impact of endogenous NO during chronic HF, the consequences of which include loss of NO-dependent modulation of ANG II-induced vasoconstriction.

Renal circulatory effects of adenosine in patients with chronic heart failure

OBJECTIVES

We sought to study the renal circulatory effects of adenosine in patients with chronic congestive heart failure (CHF).

BACKGROUND

Renal blood flow (RBF) is often reduced in patients with chronic CHF and may lead to decreased renal function. The cause of reduced RBF is multifactorial and involves systemic as well as local vasoregulatory mechanisms. Stimulation of renal adenosine A1 receptors in animal models has resulted in a significant vasoconstriction of afferent and efferent glomerular arterioles and deterioration of renal function. Although adenosine serum levels have been shown to be elevated in patients with CHF, their effect on the renal circulation in this patient population has not been studied.

METHODS

Nine patients with CHF from left ventricular systolic dysfunction were studied. The effects of adenosine at a dose of 10(-5) mol/liter infused directly into the main renal artery on heart rate, renal artery blood pressure, renal artery cross-sectional area (measured by intravascular ultrasound), renal Doppler blood flow velocity (measured by a Doppler flow wire in the renal artery), RBF and renal vascular resistance (RVR) were evaluated.

RESULTS

Infusion of adenosine resulted in no significant effect on heart rate or renal artery blood pressure but caused a substantial increase in RVR (11,204 +/- 1,469 to 31,494 +/- 3,911 dynes x s x cm(-5), p = 0.0005), which led to a marked fall in RBF in every patient (mean values 376 +/- 36 to 146 +/- 22 ml/m2, p = 0.0002). These changes in RVR and RBF were associated with no significant change in renal artery cross-sectional area (0.389 +/- 0.040 to 0.375 +/- 0.033 cm2, p = 0.3).

CONCLUSIONS

Stimulation of renal adenosine receptors in patients with CHF results in marked renal vasoconstriction that leads to an important reduction in RBF. Lack of change in renal artery cross-sectional area suggests that adenosine affects intrarenal resistance blood vessels rather than large conductance vessels. These results may indicate a rationale for investigation of renal adenosine receptor blockade for enhancement of RBF and improvement of renal function in patients with chronic CHF.