The renin-angiotensin system in heart failure

The renin-angiotensin aldosterone system does appear to have a central role in the haemodynamic and metabolic response to declining ventricular function. Human heart failure usually occurs in the setting of preceding disease, which may itself influence the underlying activity of the system. Studies of the renin-angiotensin system after myocardial infarction are in agreement with animal models, that transient activation of the renin-angiotensin system occurs. This may be sustained if the cardiac insult is severe and especially if diuretic therapy is initiated. In those patients in whom the insult is less severe, activity of the renin-angiotensin system wanes. The finding that patients with stable untreated heart failure do not have markedly activated renin-angiotensin systems is not surprising, but correction of the plasma and extracellular volume (for instance with a diuretic) will result in reappearance of activation of these systems. Since the introduction of angiotensin-converting enzyme inhibitors, several new peptides have been discovered (atrial natriuretic peptide, endothelin etc.) that have important effects on cardiovascular function. New potential therapeutic agents with actions on neuroendocrine systems, such as the atrial peptidase inhibitors, angiotensin-II receptor antagonists and renin inhibitors, are on the horizon. Such exciting new discoveries will give as much insight into the pathophysiology of heart failure as the angiotensin-converting enzyme inhibitors have done.     

Modification of myosin gene expression by imidapril in failing heart due to myocardial infarction

The beneficial effects of imidapril, an angiotensin converting enzyme (ACE) inhibitor were investigated on changes in myofibrillar ATPase as well as myosin heavy chain (MHC) content and gene expression due to myocardial infarction (MI). Three weeks after occluding the left coronary artery, rats were treated with or without imidapril (1 mg/kg/day), for 4 weeks. The infarcted hearts exhibited depressed rates of left ventricular (LV) pressure development (57+/-2.4% reduction) and pressure decay (55.5+/-1.6% reduction). LV myofibrillar Ca(2+) ATPase activity, unlike that in the right ventricle (RV), was decreased in the infarcted animals compared with controls (6.8+/-0.4 vs 10.3+/-0.6 micromol Pi/mg/hr). MHC alpha-isoform contents were decreased by 47 and 41% whereas those of MHC beta-isoform were increased by 823 and 1200% in the LV and RV due to MI, respectively. MHC alpha-isoform mRNA levels were decreased by 55 and 35% whereas those for MHC beta-isoform were increased by 50 and 30% in the infarcted LV and RV, respectively. Imidapril treatment partially prevented the changes due to MI in LV function (rate of pressure development, 24+/-2.3% reduction and rate of pressure decay, 14+/-1.8% reduction), myofibrillar Ca(2+) ATPase activity (8.2+/-0.7 micromol Pi/mg/hr), MHC protein content (alpha-MHC, 24% reduction and beta-MHC, 525% increase) and MHC gene expression (alpha-MHC, 18% reduction and beta-MHC, 15% increase). The results suggest that the beneficial effects of ACE inhibition on the failing heart are associated with improvements in myofibrillar ATPase activities as well as prevention of changes in MHC isozyme protein contents and their gene expression.     

Changes in kidney function following heart failure treatment: focus on renin-angiotensin system blockade

This article begins with a brief overview of the therapeutic agents used in the treatment of heart failure, with a special emphasis on pharmacologic agents that block the renin-angiotensin system (RAS). The discussion then builds upon the basic pathophysiology concepts introduced earlier in this issue to explain how therapies commonly used in heart failure affect kidney function. Against this background, a few of the common clinical dilemmas that clinicians often encounter when treating patients with agents that block the RAS system are discussed.     

Role of the renin-angiotensin system in the development of congestive heart failure in the dog as assessed by chronic converting-enzyme blockade

Hormonal factors may be important in the regulation of peripheral vascular resistance (PVR) in congestive heart failure (CHF). The role of the renin-angiotensin system in the development of CHF was studied in 16 unanesthetized dogs. CHF was induced by rapid right ventricular pacing, with and without chronic converting-enzyme inhibition (CEI) by captopril. The hemodynamic changes and the activity of renin, aldosterone, norepinephrine and vasopressin were studied. The control dogs showed a greater decrease in cardiac output and a greater increase of mean pulmonary artery pressure than the captopril-treated group. In the group with CEI, only a small, transient increase in PVR was observed during the development of CHF; in the control group, there was an increase of 94% of basal values. The control group showed a continual increase of renin, aldosterone and norepinephrine. Four control dogs showed an inappropriately high secretion of arginine vasopressin. The increase of sympathetic nervous activity was only insignificantly attenuated by angiotensin II inhibition and was without a considerable influence on PVR except for an early transient increase in vascular tone. In our animal model, the renin-angiotensin system plays an important role in the regulation of PVR in CHF. In this kind of CHF the sympathetic nervous system appears to be of minor importance for the long-term regulation of PVR. Plasma arginine vasopressin levels were increased in control dogs; this increase may contribute to the increased vascular tone.     

Effects of renin-angiotensin system blockade on mortality and hospitalization in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HF-PEF) is a well-recognized complication of long-standing hypertension. However, beyond the control of the traditional cardiovascular risk factors, there are few other recommendations for its management. To examine the potential benefit of renin-angiotensin system (RAS) inhibition in HF-PEF, we performed a systematic review of the published medical literature. MEDLINE, EMBASE, and COCHRANE databases were searched from 1966 to 2011 for longitudinal studies examining HF-PEF patients receiving treatment with RAS inhibitors, either ACE inhibitors (ACE-I) or angiotensin receptor blockers (ARB) in addition to their standard treatment compared to those receiving standard treatment alone. We examined the all-cause mortality, cardiovascular mortality, and hospitalizations for heart failure. A total of 12 studies with 11,259 participants were included in the analysis. Among the randomized clinical trials, with the use of RAS inhibitors over standard treatment, there was no improvement in all-cause mortality (RR: 0.99; 95 % CI: 0.88–1.12; p = 0.88), while there was a trend toward lowered rates of hospitalization (RR: 0.93; 95 % CI: 0.86–1.01; p = 0.08). There were no major differences in the outcomes between the ACE-I or ARB. However, among the observational studies with the use of RAS inhibitors, there was a significant benefit in all-cause mortality (RR: 0.76; 95 % CI: 0.62–0.93; p = 0.009), with no significant impact on the hospitalization rates. RAS inhibition in HF-PEF was not associated with significant reduction in all-cause or cardiovascular mortality, but randomized control trials appear to demonstrate a trend toward reduction in the risk for subsequent hospitalization. Further prospective randomized trials are warranted to confirm the effects of RAS inhibition on mortality and hospitalization.     

The renin-angiotensin system and experimental heart failure

Experimental studies suggest that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II (Ang II), are involved in the pathophysiology of cardiac hypertrophy and failure. All the components required for Ang II production are present in the heart, and cardiac Ang II formation appears to be regulated independent from the circulating RAS. In animal models and in patients with heart failure, the cardiac RAS is activated and, presumably, local Ang II formation is enhanced. Several cardiac cell types express Ang II type 1 (AT1) and/or type 2 (AT2)-receptors and represent potential targets for Ang II-mediated effects. In neonatal cardiac myocytes, Ang II induces a hypertrophic response via the AT1-receptor. Likewise, activation of the AT1-receptor triggers hypertrophy in terminally differentiated cardiac myocytes and in perfused heart preparations. In the neonatal system, Ang II appears to be a major autocrine/paracrine mediator of cardiac myocyte hypertrophy in response to passive mechanical stretch. By contrast, AT1-receptor activation apparently is not required to trigger load-induced hypertrophy in the adult cardiomyocyte. Recent studies suggest that the AT2-receptor opposes AT1-receptor-mediated growth signals in neonatal and in adult cardiac myocytes. Pharmacological studies have established that a blockade of the RAS at the level of the angiotensin-converting enzyme (ACE) or the AT1-receptor ameliorates the remodeling process of the heart and prolongs long-term survival in animal models of cardiac hypertrophy and failure. The therapeutic effects of ACE inhibitors and AT1-receptor antagonists clearly suggest an important role for the ACE-Ang II-AT1-receptor axis in the development of cardiac hypertrophy and failure. It must be kept in mind, however, that these drugs enhance AT2-receptor and B2-kinin receptor-dependent signaling pathways which may contribute significantly to the beneficial effects observed in vivo. Molecular and physiological analyses of transgenic mice with a cardiac-specific overexpression of the AT1 or AT2-receptor confirm that AT1 and AT2-receptor-dependent signaling cascades potently modulate cardiac myocyte function and growth. However, studies in AT1-receptor knockout mice demonstrate that cardiac hypertrophy in response to hemodynamic overload can occur independent from the AT1-receptor. In this paper, we review recent experimental evidence suggesting a critical role for the RAS in cardiac hypertrophy and failure with special emphasis on the putative role of Ang II and Ang II-receptor signaling in cardiac myocytes.     

肾素-血管紧张素系统双基因多态性与高血压合并舒张性心力衰竭的关系

目的探讨中国南方部分汉族高血压患者肾素一血管紧张素系统中血管紧张素转换酶（ACE）及血管紧张素原（AGT）双基因多态性与舒张性心力衰竭发病的关系。方法应用聚合酶链反应及限制性片断长度多态性技术,对432例高血压患者的ACE基因插入／缺失（I／D）及AGTM235T多态性进行检测。将其中207例合并舒张性心力衰竭者作为病例组,其余225例心功能正常者作为对照组。结果①病例组DD基因型及D等位基因的频率均高于对照组;②病例组TT基因型及T等位基因的频率与对照组比较差异无统计学意义;③联合分析ACE与ACT基因多态性显示,两组中同时具有DD型ACE基因及TT型AGT基因的频率分别为29．0％及14．9％,前者明显高于后者。结论DD型ACE基因可能是该地区高血压患者舒张性心力衰竭发病的遗传危险因素,ACE和AGT基因在慢性心力衰竭的发生中具有协同作用。     

Suppression of the renin-angiotensin system by intravenous digoxin in chronic congestive heart failure

Recent studies have demonstrated that therapy with digitalis preparations may be of inconsistent benefit in the treatment of chronic congestive heart failure. One explanation may be a varying effect on vasoconstrictor hormones, as digoxin has been shown to suppress plasma renin activity in normal and hypertensive persons. Therefore, the effect of short-term digoxin administration on plasma renin activity and plasma aldosterone in six patients with compensated, severe, chronic congestive heart failure was evaluated. Intravenous administration of digoxin (0.50 mg) resulted in a reduction of plasma renin activity from 4.3 ± 0.9 to 2.0 ± 0.9 ng/ml per hour and plasma aldosterone from 34 ± 16 to 14 ± 6 ng/dl (both p < 0.05). Maximal response occurred at three hours after administration, with return to baseline by seven hours. Therefore, evaluation of the role of digitalis in chronic heart failure requires consideration of its direct or indirect effect on angiotensin-mediated vasoconstriction and aldosterone-mediated sodium retention, as well as other neurohormonal mechanisms of vasoconstriction.     

肾素-血管紧张素系统基因多态性与冠心病合并慢性心力衰竭严重程度的关系

目的检测部分中国南方汉族人群冠心病合并慢性心力衰竭患者的ACE及AGT基因多态性分布情况,以探讨肾素-血管紧张素系统（1／AS）基因多态性对冠心病合并慢性心力衰竭严重程度的影响。方法应用聚合酶链反应及限制性片断长度多态性技术,对210例冠心病合并慢性心力衰竭患者的ACE基因插入／缺失（I/D）及AGT基因M235T多态性进行检测,采用彩色多普勒检测患者的左室舒张末内径（LVDD）及左室射血分数（LVEF）。结果不同ACE基因型患者其LVDD及LVEF均存在差异,LVDD（DD）〉LVDD（ID）〉LVDD（II）（P〈0．05）,LVEF（DD）〈IXEF（ID）〈LVEF（II）（P〈0．05）,不同AGT基因型亚组间LVDD及LVEF差别均无统计学意义（P〉0．05）。结论ACE基因I／D多态性与中国南方部分汉族人群冠心病合并慢性心力衰竭的严重程度相关,DD型ACE基因的冠心病患者发生心力衰竭后病情较其他基因型者更加严重。AGT基因M235T多态性似与冠心病合并慢性心力衰竭的严重程度无关。     

Interrelation of electrolytes and renin-angiotensin system in congestive heart failure

Many of the electrolyte derangements seen in chronic heart failure are related to activation of the renin-angiotensin system. Activation of the system may cause the retention of both sodium and water; the former is primarily related to the release of aldosterone and the latter is related to an angiotensin-mediated increase in thirst and decrease in the excretion of free water. The interaction of these mechanisms may explain why patients with chronic heart failure have higher values for total body sodium but lower values for serum sodium concentration than hypertensive patients or normal subjects. Activation of the renin-angiotensin system may also cause potassium depletion, which is manifest clinically by a decrease in both total body potassium and serum potassium concentration. These electrolyte disturbances may play a role in the development of ventricular arrhythmias. The renin-angiotensin system may also contribute to the development of magnesium deficits. These hormone-electrolyte interactions have important implications in the treatment of patients with heart failure, especially those in whom the renin-angiotensin system is pharmacologically inhibited.     

Combined blockade of the renin-angiotensin system]

In view of the internal counter-regulation mechanisms of the renin-angiotensin system (RAS), complete blockade would not seem to be possible if only one of its components is targeted. Instead of increasing the dosage of an angiotensin converting enzyme (ACE) inhibitor or that of an angiotensin II antagonist (AA), blockade of the system at two different levels by neutralising the internal counter-regulation mechanism could provide more effective blockade and, therefore, more pronounced biological effects. For this reason, the authors undertook two studies in a model of mild salt depletion of a normotensive subject, which showed additive effects on the lowering of the blood pressure and renin secretion during combined administration of captopril and losartan, then enalapril and losartan. There was no additive effect on plasma aldosterone levels. The administration of the ACE inhibitor neutralised the expected increases in plasma Angiotensin II values due to the losartan. All combinations of ACE inhibitor and AA were tested in spontaneous hypertensive rats using a dosage scale from 1 to 30, the results of which showed the beneficial effects of combined blockade on left ventricular mass and the deleterious effects on renal function when blockade of the RAS is too complete. Based on the results obtained in normotensive subjects and homogeneous groups of hypertensive animals, the authors conclude that low doses of an AA and of an ACE inhibitor is more effective in lowering the blood pressure than higher doses of each drug administered separately. How can these results be applied clinically in hypertension and cardiac failure? The choice between increasing the dose of each of the two drugs or the association of low doses of both drugs will depend more on the tolerance of each therapeutic strategy than on the efficacy. The choice between the two strategies will also depend on the demonstration of consequences specific to each modality of inhibition of the system, especially with respect to the effects of accumulation of bradykinin and to stimulation of type 2 receptors. The additive effects of a combined treatment should be validated by repeated administration in hypertensive patients.     

Retinal neovascularization is prevented by blockade of the renin-angiotensin system

Both angiotensin II and vascular endothelial growth factor are angiogenic agents that have recently been implicated in the pathogenesis of proliferative diabetic retinopathy. In this study, retinal neovascularization was examined in a model of retinopathy of prematurity with the use of neonatal transgenic (mRen-2)27 rats, which overexpress renin in tissues, and Sprague-Dawley rats. Blockers of the renin-angiotensin system were administered during the neovascularization period. The ACE inhibitor lisinopril and the angiotensin type 1 receptor antagonist losartan both increased retinal renin levels and prevented inner retinal blood vessel growth. Quantitative in situ hybridization revealed that the expression of vascular endothelial growth factor and its type 2 receptor in the inner retina and proliferating blood vessels were increased in rats with retinopathy of prematurity. Lisinopril reduced both retinal vascular endothelial growth factor and its type 2 receptor mRNA in retinopathy of prematurity rats, whereas losartan had no effect. It is predicted that agents that interrupt the renin-angiotensin system may play an important role as retinoprotective agents in various forms of proliferative retinopathy.     

Renal implications of the renin-angiotensin-aldosterone system blockade in heart failure

The renin-angiotensin-aldosterone system actively participates in the derangement of renal function since the early stages of heart failure (HF). A diminished capacity to excrete sodium secondary to increased proximal tubular re-absorption and loss of the renal functional reserve are the two most relevant initial alterations of renal function in which angiotensin II has been proven to act directly. Meanwhile, the octapeptide contributes to maintain glomerular filtration rate (GFR) within normal limits through efferent arteriole vasoconstriction. Administration of angiotensin converting enzyme inhibitors (ACEi) or angiotensin receptor antagonists (ARA) may thus be accompanied by a functional fall in that parameter. Advanced age, higher initial serum creatinine, history of hypertension, diabetes and atrial fibrillation predict the onset of GFR impairment associated with blockade of the renin-angiotensin system. Concomitant administration of betablockers may help to protect renal function, and preliminary data indicate that the combination of ACEi and ARA is not accompanied by a higher renal risk. The good prognostic effects of aldosterone antagonists in HF does not seem to be related to intrarenal effects of these compounds with the exception of preventing potassium loss and hypokalemia. The systematic therapeutic use of drug(s) provided with beneficial renal effects, to treat arterial hypertension or myocardial ischemia, may contribute to delay of, or prevent the development of HF.     

Preservation of glomerular filtration rate in human heart failure by activation of the renin-angiotensin system

When renal perfusion pressure is reduced in experimentally induced low-output states, glomerular filtration rate is preserved by angiotensin II-mediated efferent arteriolar vasoconstriction, but available evidence in man suggests that angiotensin II supports renal function only to the extent that it preserves systemic blood pressure. We performed simultaneous assessments of cardiac and renal function in 56 patients with severe chronic heart failure before and after 1 to 3 months of converting-enzyme inhibition. Among the 29 patients with a pretreatment renal perfusion pressure under 70 mm Hg, patients with preserved renal function (creatinine clearance greater than 50 ml/min/1.73 m2) had markedly elevated values for plasma renin activity (11.8 +/- 3.8 ng/ml/hr) and showed a significant decline in creatinine clearance after converting-enzyme inhibition (61.1 +/- 3.0 to 45.9 +/- 5.3 ml/min/1.73 m2; p less than .05). In contrast, although similar with respect to all pretreatment demographic, hemodynamic, and clinical variables, patients with a creatinine clearance under 50 ml/min/1.73 m2 had low values for plasma renin activity (3.4 +/- 0.8 ng/ml/hr) and, despite similar drug-induced decreases in systemic blood pressure, showed no change in creatinine clearance after therapy with captopril or enalapril (32.6 +/- 2.5 to 41.4 +/- 3.8 ml/min/1.73 m2). Changes in creatinine clearance varied linearly and inversely with pretreatment values for plasma renin activity (r = - .64, p less than .001); converting-enzyme inhibition effectively abolished the pretreatment difference in renal function seen in the high- and low-renin subgroups. In the 27 patients with a renal perfusion pressure of 70 mm Hg or greater, creatinine clearance did not vary significantly with plasma renin activity and was not altered by therapy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heterogeneity of myosin isozyme content of rabbit heart

A detailed study was carried out to measure the relative contents of V1 and V3 myosin isozymes in different regions of rabbit ventricle as a function of age, to assess animal-to-animal variability, and to compare different experimental approaches aimed at minimizing the effects of such variability. In addition, comparisons were made in normal developing hearts between ventricular isozyme composition and myofibrillar myosin calcium-stimulated adenosine triphosphatase. V1 isozyme predominated relative to V3 isozyme in the hearts of 2-week-old rabbits, decreasing to become a minor component in 10-week-old animals. Despite this trend, there was considerable variability in relative isozyme content of whole ventricular tissue among different rabbits of the same age. This variability was reduced in comparisons of littermates and by use of cardiac biopsies to measure changes in isozyme content in the same animal over time. Within different regions of a given heart, there also were small but significant differences in the percent V1 isozyme. The percent V1 was greatest for right ventricular papillary, followed by right ventricular free wall and then the left ventricle (free wall plus septum). There also were differences in the percent V1 within those regions, as exemplified by the significantly higher values for ventricular epicardium vs. endocardium. There was a linear correlation between the myofibrillar myosin calcium-stimulated adenosine triphosphatase and percent V1 of total isozyme for both right and left ventricles in normal and developing hearts. The regression lines for calcium-stimulated adenosine triphosphatase vs. percent V1 had a steeper slope in the left than in the right ventricle.     

The relationship of the sympathetic nervous system and the renin-angiotensin system in congestive heart failure

Congestive heart failure is a complex clinical syndrome characterized by circulatory and metabolic abnormalities. It has been apparent for more than 25 years that the sympathetic nervous system and the renin-angiotensin-aldosterone system are markedly activated in the late stages of heart failure. These two systems interact to facilitate sympathetic drive and promote salt and water retention. Circumstantial evidence is now accumulating to indicate that excessive sympathetic drive and angiotensin II activity may contribute to the pathophysiology of heart failure. These observations suggest that a dual strategy of modulating sympathetic nervous system activity to the heart while blocking angiotensin II activity may provide a rational therapeutic approach to the treatment of heart failure. Xamoterol, a beta 1 partial agonist, may enhance myocardial contractile force in the steady state, while acting to inhibit excessive sympathetic drive during exercise or severe heart failure. The concomitant use of a converting-enzyme inhibitor would be expected to blunt the detrimental effects of excessive angiotensin II activity. Modulation of adrenergic drive coupled with inhibition of marked angiotensin II activity may be potentially more effective in the treatment of congestive heart failure than either strategy used alone.