Angiotensin converting enzyme inhibition, AT1 receptor inhibition, and combination therapy with pacing induced heart failure: effects on left ventricular performance and regional blood flow patterns

Candesartan abrogates G protein-coupled receptors agonist-induced MAPK activation and cardiac myocyte hypertrophy

The renin-angiotensin-aldosterone system (RAAS) has been identified as a major contributor to the development of cardiac hypertrophy and the subsequent transition to heart failure. G protein-coupled receptors agonists such as angiotensin II (Ang II), endothelin-1 (ET-1) and phenylephrine (PE) have been implicated in hypertrophic responses in ventricular myocytes through the activation of several families of MAP kinases. In this study we examined the effect of candesartan, an Ang II type 1-(AT1)-receptor antagonist, on cardiac hypertrophy by using cultured neonatal rat cardiomyocytes. Stimulation with Ang II (100 nM), ET-1 (100 nM) or PE (1 µM) induced marked increases in [3H]Leucine incorporation (≥ 50%), compatible with enhanced protein synthesis. The addition of candesartan abrogated the increase in [3H]Leucine incorporation in response not only to Ang II but also to ET-1 and PE. To elucidate the mechanisms involved in this antihypertrophic effect of candesartan, we studied the activation of p38-MAPK, extracellular signal-regulated kinases (ERK1/2) and stress-activated protein kinases (SAPKs). Ang II, ET-1 and PE increased the phosphorylation levels of ERK1/2, p54 SAPK and p46SAPK and p38 in a time-dependent manner. This activation was completely blocked in the case of Ang II by pretreatment with candesartan. ET-1-induced activation of ERKs, SAPKs and p38 was also partially, but significantly, reduced by candesartan. PE-induced activation of SAPKs, but not ERKs and p38, was also reduced by candesartan. These results suggest that the hypertrophic response to ET-1 and PE, along with Ang II, is dependent upon a functioning AT1-receptor and may be mediated by AT 1 activation of the MAP kinases.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Small and large animal models in cardiac contraction research: advantages and disadvantages

The mammalian heart is responsible for not only pumping blood throughout the body but also adjusting this pumping activity quickly depending upon sudden changes in the metabolic demands of the body. For the most part, the human heart is capable of performing its duties without complications; however, throughout many decades of use, at some point this system encounters problems. Research into the heart's activities during healthy states and during adverse impacts that occur in disease states is necessary in order to strategize novel treatment options to ultimately prolong and improve patients' lives. Animal models are an important aspect of cardiac research where a variety of cardiac processes and therapeutic targets can be studied. However, there are differences between the heart of a human being and an animal and depending on the specific animal, these differences can become more pronounced and in certain cases limiting. There is no ideal animal model available for cardiac research, the use of each animal model is accompanied with its own set of advantages and disadvantages. In this review, we will discuss these advantages and disadvantages of commonly used laboratory animals including mouse, rat, rabbit, canine, swine, and sheep. Since the goal of cardiac research is to enhance our understanding of human health and disease and help improve clinical outcomes, we will also discuss the role of human cardiac tissue in cardiac research. This review will focus on the cardiac ventricular contractile and relaxation kinetics of humans and animal models in order to illustrate these differences.

Hemodynamics and myocardial blood flow patterns after placement of a cardiac passive restraint device in a model of dilated cardiomyopathy

BACKGROUND

The present study examined a cardiac passive restraint device which applies epicardial pressure (HeartNet Implant; Paracor Medical, Inc, Sunnyvale, Calif) in a clinically relevant model of dilated cardiomyopathy to determine effects on hemodynamic and myocardial blood flow patterns.

METHODS

Dilated cardiomyopatht was established in 10 pigs (3 weeks of atrial pacing, 240 beats/min). Hemodynamic parameters and regional left ventricular blood flow were measured under baseline conditions and after acute placement of the HeartNet Implant. Measurements were repeated after adenosine infusion, allowing maximal coronary vasodilation and coronary flow reserve to be determined.

RESULTS

Left ventricular dilation and systolic dysfunction occurred relative to baseline as measured by echocardiography. Left ventricular end-diastolic dimension increased and left ventricular fractional shortening decreased (3.8 ± 0.1 vs 6.1 ± 0.2 cm and 31.6% ± 0.5% vs 16.2% ± 2.1%, both P < .05, respectively), consistent with the dilated cardiomyopathy phenotype. The HeartNet Implant was successfully deployed without arrhythmias and a computed median mid-left ventricular epicardial pressure of 1.4 mm Hg was applied by the HeartNet Implant throughout the cardiac cycle. Acute HeartNet placement did not adversely affect steady state hemodynamics. With the HeartNet Implant in place, coronary reserve was significantly blunted.

CONCLUSIONS

In a large animal model of dilated cardiomyopathy, the cardiac passive restraint device did not appear to adversely affect basal resting myocardial blood flow. However, after acute HeartNet Implant placement, left ventricular maximal coronary reserve was blunted. These unique results suggest that cardiac passive restraint devices that apply epicardial transmural pressure can alter myocardial blood flow patterns in a model of dilated cardiomyopathy. Whether this blunting of coronary reserve holds clinical relevance with chronic passive restraint device placement remains unestablished.

Role of blood flow in carotid body chemoreflex function in heart failure

Peripheral chemoreflex sensitivity is potentiated in clinical and experimental chronic heart failure (CHF). Blood supply to tissues is inevitably reduced in CHF. However, it remains poorly understood whether the reduced blood flow is the cause of increased peripheral chemoreflex sensitivity in CHF. This work highlights the effect of chronically reduced blood flow to the carotid body (CB) on peripheral chemoreflex function in rabbits. In pacing-induced CHF rabbits, blood flow in the carotid artery was reduced by 36.4 ± 5.2% after 3 weeks of pacing. For comparison, a similar level of blood flow reduction was induced by carotid artery occlusion (CAO) over a similar 3 week time course without pacing. CB blood supply was reduced by similar levels in both CHF and CAO rabbits as measured with fluorescent microspheres. Compared with sham rabbits, CAO enhanced peripheral chemoreflex sensitivity in vivo, increased CB chemoreceptor activity in an isolated CB preparation and decreased outward potassium current (Ik) in CB glomus cells to levels similar to those that were observed in CHF rabbits. In CAO CB compared to sham, neural nitric oxide (NO) synthase (nNOS) expression and NO levels were suppressed, and angiotensin II (Ang II) type 1 receptor (AT1-R) protein expression and Ang II concentration were elevated; these changes were similar to those seen in the CB from CHF rabbits. A NO donor and AT1-R antagonist reversed CAO-enhanced chemoreflex sensitivity. These results suggest that a reduction of blood flow to the CB is involved in the augmentation of peripheral chemoreflex sensitivity in CHF.

Aprotinin modifies left ventricular contractility and cytokine release after ischemia-reperfusion in a dose-dependent manner in a murine model

BACKGROUND

Periods of ischemia-reperfusion (I/R) during cardiac surgery are associated with transient left ventricular (LV) dysfunction and an inflammatory response. In this study, we examined the potential dose-dependent effects of aprotinin (APRO) on LV contractility and cytokine release in the setting of I/R.

METHODS

An index of LV contractility, LV maximal elastance (E(max)), was measured at baseline, 30 min of ischemia, and 60 min of reperfusion by microtransducer volumetry. Mice were randomized as follows: (a) APRO 20,000 kallikrein-inhibiting units (KIU)/kg (n = 11); (b) APRO 4 x 10(4) KIU/kg (n = 10); (c) APRO 8 x 10(4) KIU/kg (n = 10); and (d) vehicle (saline; n = 10). APRO doses were calculated to reflect half, full, and twice the clinical Hammersmith dosing schedule. After I/R, plasma was collected for cytokine measurements.

RESULTS

After I/R, E(max) decreased from the baseline value by more than 40% in the vehicle group as well as in the APRO 4 x 10(4) KIU/kg and APRO 8 x 10(4) KIU/kg groups (P < 0.05). However, E(max) returned to near baseline values in the APRO 2 x 10(4) KIU/kg group. Tumor necrosis factor (TNF) increased 10-fold after I/R, but it was reduced with higher APRO doses.

CONCLUSIONS

This study demonstrated that a low dose of APRO provided protective effects on LV contractility, whereas higher doses suppressed TNF release. These unique findings suggest that there are distinct and independent mechanisms of action of APRO in the context of I/R.

Control of pulmonary vascular tone during exercise in health and pulmonary hypertension

Despite the importance of the pulmonary circulation as a determinant of exercise capacity in health and disease, studies into the regulation of pulmonary vascular tone in the healthy lung during exercise are scarce. This review describes the current knowledge of the role of various endogenous vasoactive mechanisms in the control of pulmonary vascular tone at rest and during exercise. Recent studies demonstrate an important role for endothelial factors (NO and endothelin) and neurohumoral factors (noradrenaline, acetylcholine). Moreover, there is evidence that natriuretic peptides, reactive oxygen species and phosphodiesterase activity can influence resting pulmonary vascular tone, but their role in the control of pulmonary vascular tone during exercise remains to be determined. K-channels are purported end-effectors in control of pulmonary vascular tone. However, K(ATP) channels do not contribute to regulation of pulmonary vascular tone, while the role of K(V) and K(Ca) channels at rest and during exercise remains to be determined. Pulmonary hypertension is associated with alterations in pulmonary vascular function and structure, resulting in blunted pulmonary vasodilatation during exercise and impaired exercise capacity. Although there is a paucity of studies pertaining to the regulation of pulmonary vascular tone during exercise in idiopathic pulmonary hypertension, the few studies that have been performed in models of pulmonary hypertension secondary to left ventricular dysfunction suggest altered control of pulmonary vascular tone during exercise. Since the increased pulmonary vascular tone during exercise limits exercise capacity, future studies are needed to investigate the vasomotor mechanisms that are responsible for the blunted exercise-induced pulmonary vasodilatation in pulmonary hypertension.

Myocardial protection in the failing heart: II. Effect of pulsatile cardioplegic perfusion under simulated left ventricular restoration

OBJECTIVE

The open ventricle was studied in pacing-induced experimental heart failure to determine the extent of coronary perfusion and distribution during either continuous or pulsatile cardioplegic perfusion compared with whole blood in the beating heart.

METHODS

In 5 animals that underwent pacing-induced heart failure and in 6 control swine, regional coronary blood flows were measured on bypass in the open left ventricle (simulating exposure for left ventricle restoration) during (1) beating, (2) nonpulsatile cardioplegia, and (3) pulsatile cardioplegia modalities. Mean perfusion pressure was maintained at 80 mm Hg.

RESULTS

Flow magnitude and distribution differed in control and failing hearts in the open left ventricle. In control hearts, transmural and endocardial cardioplegic flow of nonpulsatile and pulsatile flow (which were similar to each other) exceeded beating flow by 63% and 70%, respectively, in the open left ventricle condition. Transmural and subendocardial vascular resistance increased in failing hearts during cardioplegic delivery, resulting in lower subendocardial flow under nonpulsatile conditions for the same perfusion pressure. In failing hearts, subendocardial perfusion conditions did not change in the beating state (0.89 vs 0.78 mL/min/g in control and failing open beating states, respectively), but nonpulsatile cardioplegic flow was significantly reduced by 154%, and became lower than beating flow by 32.2% (0.78 vs 0.59 mL/min/g). Conversely, pulsatile cardioplegic delivery improved endocardial flow in the open failing hearts, as cardioplegic perfusion with pulsatility exceeded beating flow by 41%. In heart failure, pulsatility from either the beating heart, which causes extrinsic compression of coronary vessels, or intrinsic vessel distension during pulsatile cardioplegic perfusion preserved endocardial perfusion better than nonpulsatile cardioplegia at the same perfusion pressure.

CONCLUSION

In the failing open ventricle (simulated geometry during ventricular restoration), subendocardial blood flow was maintained in the beating state, but decreased significantly from control values during nonpulsatile cardioplegic perfusion. Conversely, pulsatile cardioplegic delivery improved subendocardial perfusion of the open failing ventricle. These findings of improved subendocardial perfusion during pulsatile delivery (either during beating or cardioplegic perfusion) compared with nonpulsatile cardioplegic delivery may have important implications for myocardial protection in failing hearts.

Myocardial protection in the failing heart: I. Effect of cardioplegia and the beating state under simulated left ventricular restoration

OBJECTIVE

Heart failure was induced by cardiac pacing to evaluate myocardial flow distribution of the open ventricle during delivery of either cardioplegia or in the beating state during simulated left ventricular restoration.

METHODS

Studies included 5 (pacing-induced) failing pig hearts and 6 control hearts. Pacing-induced cardiac failure reduced fractional shortening by approximately 22%, increased left ventricular end-diastolic diameter by 34%, caused pulmonary hypertension (mean blood pressure increased from 12 to 35 mm Hg), and led to significant ascites. Global and regional coronary blood flow were measured with microspheres during cardiopulmonary bypass at 80 mm Hg perfusion pressure in either vented (collapsed) or open (exposure by traction for left ventricular restoration) left ventricles during continuous perfusion under either beating-heart or cardioplegic conditions.

RESULTS

In control hearts, venting and exposure ventriculotomy did not affect flow. In failing hearts decompressed by venting, coronary flow was lower during the beating and cardioplegic delivery than during control conditions at the same perfusion pressure of 80 mm Hg. Mean cardioplegic flow during ventricular decompression by venting exceeded beating flow by 97%. Conversely, traction to increase the ventricular radius during exposure ventriculotomy reduced endocardial cardioplegic coronary blood flow by 64% (from 0.97 to 0.59 mL/[min x g]), whereas the beating state raised endocardial flow by 95% (from 0.40 to 0.78 mL/[min x g]). Changing ventricular shape changed coronary vascular resistance in failing hearts during beating or cardioplegic delivery.

CONCLUSIONS

Coronary blood flow alterations occurred only in failing hearts when geometry was changed from closed to open state. The beating method provided more endocardial flow than cardioplegic delivery during ventricular exposure for restoration. Vascular remodeling raised coronary vascular resistance in failing hearts, thereby requiring higher pressure for similar blood flows.

Role of angiotensin II type 2 receptors and kinins in the cardioprotective effect of angiotensin II type 1 receptor antagonists in rats with heart failure

OBJECTIVES

We studied the role of angiotensin II type 2 (AT(2)) receptors and kinins in the cardioprotective effect of angiotensin II type 1 antagonists (AT(1)-ant) in rats with heart failure (HF) after myocardial infarction.

BACKGROUND

The AT(1)-ant is as effective as angiotensin-converting enzyme inhibitors in treating HF, but the mechanisms whereby AT(1)-ant exert their benefits on HF in vivo are more complex than previously understood.

METHODS

Brown Norway Katholiek rats (BNK), which are deficient in kinins because of a mutation in the kininogen gene, and their wild-type control (Brown Norway [BN]) underwent myocardial infarction. Two months later, they were treated for two months with: 1) vehicle; 2) AT(1)-ant (L158809, Merck, Rahway, New Jersey); 3) AT(1)-ant + AT(2)-ant (PD-123319, Parke Davis, Ann Arbor, Michigan); or 4) AT(1)-ant + kinin B(2) receptor antagonist (B(2)-ant) (icatibant) (only BN). We measured left ventricular weight (LVW) gravimetrically, myocyte cross-sectional area (MCSA) and interstitial collagen fraction (ICF) histologically, and ejection fraction by ventriculography.

RESULTS

Development of HF was comparable in BN and BNK rats. The AT(1)-ant reduced LVW and MCSA and the AT(2)-ant blocked these effects in BN rats, but the B(2)-ant did not. The AT(1)-ant reduced LVW and MCSA in BNK rats, and this effect was reversed by the AT(2)-ant. In BN rats, ICF was reduced and LVEF increased by AT(1)-ant, and both AT(2)-ant and B(2)-ant reversed these effects. In BNK rats, the AT(1)-ant failed to reduce ICF, and its therapeutic effect on LVEF was significantly blunted.

CONCLUSIONS

In HF, the AT(2) receptor plays an important role in the therapeutic effects of AT(1)-ant, and this effect may be mediated partly through kinins; however, kinins appear to play a lesser role in the antihypertrophic effect of AT(1)-ant.

Combined Treatment with an AT1 Receptor Blocker and Angiotensin Converting Enzyme Inhibitor Has an Additive Effect on Inhibiting Neointima Formation via Improvement of Nitric Oxide Production and Suppression of Oxidative Stress

Accumulating evidence shows that inhibition of the vascular renin-angiotensin system results in suppression of injury-elicited neointima formation. We attempted to determine whether or not combined treatment with an angiotensin II type 1 receptor blocker (ARB) and angiotensin converting enzyme inhibitor (ACEI) has an additive inhibitory effect on balloon-injury-elicited neointima formation in the carotid artery. Male Sprague-Dawley rats were treated with an ARB (valsartan: 3 mg/kg/day) and/or an ACEI (benazepril: 0.3 mg/kg/day) from 1 week before until 2 weeks after balloon injury. Experiments were also conducted with one-third of the dose combination used in the original experiments. Both ARB and ACEI inhibited neointima formation without any blood pressure changes. The full-dose combination lowered blood pressure and suppressed neointima formation significantly compared with the levels in the groups treated with either ACEI or ARB alone. The low-dose combination without blood pressure reduction also inhibited neointima formation to a similar extent as the full-dose combination. We measured 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a marker of oxidative stress, and nitrite and nitrate (NOx), an index of nitric monoxide production, in media conditioned by the injured artery. NOx production was lower and 8-iso-PGF2alpha was higher in the media of the injured artery, compared with those in the normal artery. ACEI restored NOx production more dramatically than ARB, and ARB suppressed 8-iso-PGF2alpha markedly compared with ACEI. These results suggest that the combination of an ARB and an ACEI exerts an additive inhibitory effect, presumably through an increase in production and bioavailability of NO from the endothelium.

Angiotensin II type 1 receptor A1166C polymorphism and prophylactic indomethacin treatment induced ductus arteriosus closure in very low birth weight neonates

Altered pulmonary vascular resistance might be a factor for delayed closure of the ductus arteriosus (DA) in preterm infants. Angiotensin II plays a central role in the elevation of pulmonary vascular resistance. Angiotensin II exerts its vasoconstrictor effect on the angiotensin II type 1 receptor (AT1R). Homozygous carriers of the AT1R A1166C genetic variant present an exaggerated vasoconstrictor response to angiotensin II. We have investigated whether the presence of AT1R CC1166 influences the effect of prophylactic indomethacin treatment on the closure of DA until the fifth postnatal day in preterm infants. In this retrospective study detailed medical history of the first postnatal week was obtained in 159 infants born before the 33rd gestational week. All were treated by prophylactic indomethacin to induce permanent closure of the DA. On the sixth postnatal day the DA was still open in 56, whereas it was permanently closed in 103. The AT1R A1166C genotype of the infants was determined from Guthrie spots. Stepwise binary logistic regression analysis was used to assess the effect of medical conditions and genotype on the risk of patent DA (PDA). Birth weight, infantile respiratory distress, and severe hypotension were independent risk factors for PDA (p < 0.01, p < 0.05, p < 0.05, respectively). The carrier state of AT1R CC1166 was protective against PDA (p < 0.05; odds ratio, 0.067). AT1R AC1166 genotype was not associated with PDA. Our results indicate that the risk of PDA might be lower in infants of AT1R CC1166 than in those with AC or AA genotypes.

Pharmacologic Blockade of the Renin-Angiotensin System: Vascular Benefits Beyond Commonly Understood Pharmacologic Actions

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) are recognized primarily for their use in hypertension, in heart failure, and after myocardial infarction. New evidence, particularly with ACE inhibitors, has shown their ability to reduce acute coronary events associated with atherosclerosis in patients without a history of the aforementioned cardiac conditions. This is likely due to inhibitory effects on the renin-angiotensin system--a system that adversely influences fibrinolytic balance, vascular endothelial function, and vascular inflammation, all key components of atherosclerotic progression and adverse coronary outcomes. Results of various studies suggest favorable effects of ACE inhibitors and ARBs on markers of these components, including effects on plasminogen activator inhibitor-1, endothelin-1, and nitric oxide by ACE inhibitors, and effects on vascular cell adhesion molecule-1 and C-reactive protein by ARBs. Although early evidence suggests that ACE inhibitors may provide a greater beneficial effect on some of these markers compared with ARBs, and that certain ACE inhibitors may provide greater vascular benefits than others, further investigation is required to verify such findings. Overall, understanding the distinct coronary vascular benefits of these agents will emphasize the importance of using them, particularly ACE inhibitors, to improve outcomes in patients with coronary atherosclerotic disease.

Angiotensin-converting enzyme inhibitors improve coronary flow reserve in dilated cardiomyopathy by a bradykinin-mediated, nitric oxide-dependent mechanism

BACKGROUND

ACE inhibitors have been used extensively in heart failure, where they induce systemic vasodilatation. ACE inhibitors have also been shown to reduce ischemic events after myocardial infarction, although their mechanisms of action on the coronary circulation are less well understood. The purpose of the present study was to determine the effects and the mechanism of action of the ACE inhibitor enalaprilat and the AT1 antagonist losartan on regional myocardial perfusion and coronary flow and vasodilator reserve in conscious dogs with pacing-induced dilated cardiomyopathy (DCM).

METHODS AND RESULTS

Twenty-seven conscious, chronically instrumented dogs were studied during advanced stages of dilated cardiomyopathy, which was induced by rapid pacing. Enalaprilat (1.25 mg IV) improved transmural distribution (endocardial/epicardial ratio) at rest (baseline, 0.91+/-0.11; enalaprilat, 1.02+/-0.07 mL/min per g; P<0.05) and during atrial pacing (baseline, 0.82+/-0.11; enalaprilat, 0.98+/-0.07; P<0.05). Enalaprilat also restored subendocardial coronary flow reserve (CFR) (baseline CFR, 1.89+/-0.11; enalaprilat CFR, 2.74+/-0.33; P<0.05) in DCM. These effects were abolished by pretreatment with the NO synthase inhibitor nitro-L-arginine. The effects were recapitulated by the bradykinin(2) receptor agonist cereport but not by the AT1 antagonist losartan.

CONCLUSIONS

The ACE inhibitor enalaprilat improves transmural myocardial perfusion at rest and after chronotropic stress and restores impaired subendocardial coronary flow and vasodilator reserve in DCM. The effects of enalaprilat were bradykinin mediated and NO dependent and were not recapitulated by losartan. These data suggest beneficial effects of ACE inhibitors on the coronary circulation in DCM that are not shared by AT1 receptor antagonists.

Effects of losartan and its combination with quinapril on the cardiac sympathetic nervous system and neurohormonal status in essential hypertension

OBJECTIVE

Sympathetic nervous and renin-angiotensin systems play important roles in essential hypertension. This study was aimed at assessing the effects of losartan or its combination with quinapril on the cardiac nervous system and neurohormonal status in essential hypertension.

DESIGN AND METHODS

Randomized, comparative study of 105 patients with mild essential hypertension, carried out at Shizuoka General Hospital. In phase 1, 40 hypertensives were allocated randomly into the losartan (50 mg) group or the quinapril (10 mg) group. In phase 2, 65 hypertensives, after 3 months 10 mg quinapril monotherapy, were allocated randomly into groups with 50 mg losartan (n = 32) or 5 mg amlodipine (n = 33) added to quinapril, and were treated for a further 3 months. All patients underwent [(123)I]metaiodobenzylguanidine (MIBG) imaging and neurohormonal measurements before and 3 months after treatment.

RESULTS

Both monotherapies significantly increased renin activity, while losartan monotherapy also increased angiotensin II (AII) concentration. In both the losartan and quinapril groups, the washout rate was significantly decreased (18.1 +/- 11.4 versus 13.9 +/- 11.0%, P < 0.0002 and 13.3 +/- 9.3 versus 12.3 +/- 9.1%, P < 00001, respectively) without changes in the heart to mediastinum ratio (H/M ratio). Both combined therapies lowered blood pressure to similar levels. A combination therapy with losartan and quinapril significantly increased the H/M ratio (1.93 +/- 0.29 and 2.02 +/- 0.29, P < 0.01) and decreased the washout rate (17.6 +/- 11.0 and 15.3 +/- 9.2%, P < 0.02) without affecting AII concentration, whereas a combination therapy with amlodipine and quinapril therapy did not affect the scintigraphic parameters with an increase in the AII concentration.

CONCLUSIONS

With a usual antihypertensive dose, both losartan and quinapril had a little suppressive effect on the cardiac sympathetic activity in essential hypertension. In contrast, the combination therapy with losartan and quinapril, which results in a higher degree of inhibition of the renin-angiotensin system, could suppress the cardiac sympathetic activity effectively.

Long-term angiotensin-converting enzyme and angiotensin I--receptor inhibition in pacing-induced heart failure: effects on myocardial interstitial bradykinin levels

BACKGROUND

We examined whether and to what degree long-term angiotensin-converting enzyme (ACE) inhibition, angiotensin type 1 (AT(1))-receptor blockade, or combined inhibition in developing congestive heart failure (CHF) alter myocardial interstitial bradykinin (BF) levels.

METHODS AND RESULTS

Pigs (27-30 kg) underwent rapid pacing-induced CHF (240 bpm, 3 weeks; n = 10); pacing CHF with concomitant ACE inhibition (benezaprilat, 3.75 mg/day; n = 10); pacing CHF and concomitant AT(1)-receptor blockade (valsartan, 60 mg/day; n = 10); pacing CHF and combined inhibition (benezaprilat/valsartan, 1.87/60 mg/day, respectively; n = 10); or served as controls (no pacing, no treatment; n = 10). Steady-state myocardial interstitial BK levels were quantitated by microdialysis. Cardiac output decreased to 1.95 +/- 0.18 L/min in pacing CHF compared with control (3.78 +/- 0.38; P < .05). Cardiac output increased from untreated CHF values with concomitant ACE inhibition (3.91 +/- 0.27 L/min), AT(1)-receptor blockade (3.30 +/- 0.41 L/min), or combined ACE/AT(1)-receptor inhibition (4.13 +/- 0.32 L/min; all P < .05 v CHF). With pacing CHF, myocardial interstitial BK levels were reduced by approximately 50% from control values and were normalized in the ACE inhibition and combined inhibition groups.

CONCLUSIONS

Long-term ACE inhibition increases myocardial interstitial BK levels with CHF; addition of AT(1)-receptor blockade does not seem to abrogate these effects.

Myocardial bradykinin following acute angiotensin-converting enzyme inhibition, AT1 receptor blockade, or combined inhibition in congestive heart failure

BACKGROUND

The present study examined the effects of acute angiotensin-converting enzyme inhibition (ACEI), AT(1) receptor blockade (AT(1) block), or combined treatment on in vitro and in vivo bradykinin (BK) levels.

METHODS

BK levels were measured in isolated porcine myocyte preparations (n = 13) in the presence of exogenous BK (10(-8) M); with an ACEI (benezaprilat; 0.1 mM) and BK; an AT(1) block (valsartan; 10(-5) M) and BK; and combined treatment and BK. In a second study, myocardial microdialysis was used to measure porcine interstitial BK levels in both normal (n = 14) and pacing-induced congestive heart failure (CHF) (240 beats/min, 3 weeks, n = 16) under the following conditions: baseline, following ACEI (benezaprilat, 0.0625 mg/kg) or AT(1) block (valsartan, 0.1 mg/kg), and a combined treatment (benezaprilat, 0.0625 mg/kg; valsartan, 0.1 mg/kg).

RESULTS

In the left ventricular myocyte study, BK levels increased over 93% with all treatments compared to untreated values (P < 0.05). In the in vivo study, basal interstitial BK values were lower in the CHF group than in controls (2.64 +/- 0.57 vs 5.91 +/- 1.4 nM, respectively, P < 0.05). Following acute infusion of the ACEI, BK levels in the CHF state increased from baseline (57% +/- 22; P < 0.05). Following combined ACEI/AT(1) block, BK levels increased from baseline in both control (42% +/- 11) and CHF groups (60% +/- 22; P < 0.05 for both).

CONCLUSION

These findings suggest that ACEI, or combined ACEI/AT(1) block increased BK at the level of the myocyte and potentiated BK levels in the CHF myocardial interstitium.

Difficult cases in heart failure: Raison d'Être behind ACE inhibitors and AT1 receptor combinations in chronic heart failure: chemical nuances or clinical significance?

The following case description serves to illustrate the difficulties often faced in clinical practice in implementing what appear to be fairly simple and clear evidence-based guidelines regarding angiotensin-converting enzyme (ACE) inhibitors and no clear guidelines regarding angiotensin receptor blocker (ARB) use or, more importantly, ACE inhibitor and ARB combinations in chronic heart failure. (c)2001 by CHF, Inc.

Angiotensin receptor blockers: evidence for preserving target organs

Hypertension is a major problem throughout the developed world. Although current antihypertensive treatment regimens reduce morbidity and mortality, patients are often noncompliant, and medications may not completely normalize blood pressure. As a result, current therapy frequently does not prevent or reverse the cardiovascular remodeling that often occurs when blood pressure is chronically elevated. Blockade of the renin-angiotensin system (RAS) is effective in controlling hypertension and treating congestive heart failure. Both angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) inhibit the activity of the RAS, but these two classes of antihypertensive medications have different mechanisms of action and different pharmacologic profiles. Angiotensin-converting enzyme inhibitors block a single pathway in the production of angiotensin II (Ang II). In addition, angiotensin I is not the only substrate for ACE. The ACE inhibitors also block the degradation of bradykinin that may have potential benefits in cardiovascular disease. Bradykinin is, however, the presumed cause of cough associated with ACE inhibitor therapy. Data from clinical trials on ACE inhibitors serve to support the involvement of the RAS in the development of cardiovascular disease. Angiotensin receptor blockers act distally in the RAS to block the Ang II type 1 (AT1) receptor selectively. Thus, ARBs are more specific agents and avoid many side effects. Experimental and clinical trials have documented the efficacy of ARBs in preserving target-organ function and reversing cardiovascular remodeling. In some instances, maximal benefit may be obtained with Ang II blockade using both ARBs and ACE inhibitors. This review describes clinical trials that document the efficacy of ARBs in protecting the myocardium, blood vessels, and renal vasculature.

Expression and activity of pulmonary endothelin converting enzyme in heart failure: relation to endothelin biosynthesis and receptor distribution

BACKGROUND

Although reduced pulmonary clearance of endothelin-1 (ET-1) has been suggested to contribute to increased circulating levels in congestive heart failure (CHF), the regulation of the pulmonary ET system with CHF remains to be defined. Accordingly, the aim of the present study is to investigate the expression and activity of the ET system with the development of CHF.

METHODS AND RESULTS

Pulmonary tissue samples were collected from pigs with pacing CHF (240 bpm, 3 wks, n = 10) and controls (n = 10). The pulmonary messenger RNA (mRNA) and protein levels of endothelin converting enzyme-1 (ECE-1) subisoforms, ET-1, and ET receptor profiles were determined. The gene expression of ET-1 precursor, ECE-1a, and ET(A) was upregulated 4-, 3-, and 2-fold, respectively, with CHF. Pulmonary tissue ET-1 was increased to 13 +/- 2 fmol/mg protein from control values of 5 +/- 1 fmol/mg protein (P <.05), and ECE-1 activity was augmented from 3,264 +/- 665 fmol/mg protein in control animals to 14,073 +/- 654 fmol/mg protein per hour in CHF animals (P <.05). The ET(B) receptor density decreased, whereas ET(A) receptors were increased in CHF, indicating a shift in the ET(A) to ET(B) ratio.

CONCLUSIONS

Both the increased synthesis and the decreased clearance of ET-1 via ET(B) receptors may contribute to the increased systemic and pulmonary ET-1 levels in CHF.

Renin-angiotensin system inhibition on noradrenergic nerve terminal function in pacing-induced heart failure

Chronic angiotensin-converting enzyme (ACE) inhibition has been shown to improve cardiac sympathetic nerve terminal function in heart failure. To determine whether similar effects could be produced by angiotensin II AT(1) receptor blockade, we administered the ACE inhibitor quinapril, angiotensin II AT(1) receptor blocker losartan, or both agents together, to rabbits with pacing-induced heart failure. Chronic rapid pacing produced left ventricular dilation and decline of fractional shortening, increased plasma norepinephrine (NE), and caused reductions of myocardial NE uptake activity, NE histofluorescence profile, and tyrosine hydroxylase immunostained profile. Administration of quinapril or losartan retarded the progression of left ventricular dysfunction and attenuated cardiac sympathetic nerve terminal abnormalities in heart failure. Quinapril and losartan together produced greater effects than either agent alone. The effect of renin-angiotensin system inhibition on improvement of left ventricular function and remodeling, however, was not sustained. Our results suggest that the effects of ACE inhibitors are mediated via the reduction of angiotensin II and that angiotensin II plays a pivotal role in modulating cardiac sympathetic nerve terminal function during development of heart failure. The combined effect of ACE inhibition and angiotensin II AT(1) receptor blockade on cardiac sympathetic nerve terminal dysfunction may contribute to the beneficial effects on cardiac function in heart failure.

Rationale for the use of combination angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker therapy in heart failure

BACKGROUND

Heart failure (HF) is a major cause of morbidity and mortality in the United States. The renin-angiotensin system (RAS) plays a major role in its pathophysiology, and angiotensin-converting enzyme (ACE) inhibitors are the cornerstone of therapy. However, HF continues to progress despite this therapy, perhaps because of production of angiotensin II by alternative pathways, which lead to direct stimulation of the angiotensin II receptor. Angiotensin II receptor blocker (ARB) therapy alone or in combination with the ACE inhibitor is a promising approach to block the RAS and slow HF progression more completely.

METHODS

The current medical literature on the pathophysiology of HF and the use of ACE inhibitors and ARBs was extensively reviewed.

RESULTS

Evidence from basic science, experimental animals, and clinical trials provides data on the safety and efficacy of RAS inhibition with ACE inhibitors and ARBs as monotherapy and in combination. Data from the Evaluation of Losartan in the Elderly (ELITE) II trial indicate that ARBs alone do not appear to be more effective than ACE inhibitors in HF, but studies evaluating their use in combination are currently ongoing.

CONCLUSIONS

The addition of an ARB offers more complete angiotensin II receptor blockade of the RAS than can be obtained by ACE inhibitors alone. Combination therapy preserves the benefits of bradykinin potentiation offered by ACE inhibitors while providing potential antitrophic influences of AT(2) receptor stimulation and may play an increased role in the treatment of chronic HF in the future.

Enhanced reduction of myocardial infarct size by combined ACE inhibition and AT(1)-receptor antagonism

The effects of the angiotensin-converting-enzyme inhibitor (ACEI) ramiprilat, the angiotensin II type 1 receptor antagonist (AT(1)A) candesartan, and the combination of both drugs on infarct size (IS) resulting from regional myocardial ischaemia were studied in pigs. Both ACEI and AT(1)A reduce myocardial IS by a bradykinin-mediated process. It is unclear, however, whether the combination of ACEI and AT(1)A produces a more pronounced IS reduction than each of these drugs alone. Forty-six enflurane-anaesthetized pigs underwent 90 min low-flow ischaemia and 120 min reperfusion. Systemic haemodynamics (micromanometer), subendocardial blood flow (ENDO, microspheres) and IS (TTC-staining) were determined. The decreases in left ventricular peak pressure by ACEI (by 9+/-2 (s.e. mean) mmHg), AT(1)A (by 11+/-2 mmHg) or their combination (by 18+/-3 mmHg, P<0.05 vs ACEI and AT(1)A, respectively) were readjusted by aortic constriction prior to ischaemia. With placebo (n=10), IS averaged 20.0+/-3.3% of the area at risk. IS was reduced to 9.8+/-2.6% with ramiprilat (n=10) and 10.6+/-3.1% with candesartan (n=10). Combined ramiprilat and candesartan (n=10) reduced IS to 6.7+/-2.1%. Blockade of the bradykinin-B(2)-receptor with icatibant prior to ACEI and AT(1)A completely abolished the reduction of IS (n=6, 22.8+/-6.1%). The relationship between IS and ischaemic ENDO with placebo was shifted downwards by each ACEI and AT(1)A and further shifted downwards with their combination (P<0.05 vs all groups); icatibant again abolished such downward shift. The combination of ACEI and AT(1)A enhances the reduction of IS following ischaemia/reperfusion compared to a monotherapy by either drug alone; this effect is mediated by bradykinin.

Combination therapy with angiotensin converting enzyme inhibition and AT1 receptor inhibitor on ventricular remodeling after myocardial infarction in rats

BACKGROUND

There are limited data regarding the effects of angiotensin II receptor blockade after myocardial infarction (MI). In addition, whether combined angiotensin converting enzyme (ACE) inhibitor and angiotensin II type I (AT(1)) receptor antagonist may be superior to either drug alone on ventricular remodeling remains unclear. The goal of this study was to determine if the cardiac effects of the combined administration of an ACE inhibitor and AT(1) receptor antagonist are greater than those produced by either of these agents administered individually after MI.

METHODS AND RESULTS

After MI, rats were divided into 4 groups: 1) untreated animals, 2) lisinopril treatment (20 mg/kg/day), 3) losartan treatment (20 mg/kg/day), and 4) lisinopril plus losartan treatment. After 3 months, the cardiac parameters studied were: mortality, fibrosis (hydroxyproline), hypertrophy (ventricular weight/body weight ratio [VW/BW]), left ventricular enlargement (volume at end-diastolic pressure equaled zero/body weight ratio [V0/BW]), and ventricular function (isovolumetric developed pressure, dp/dt, -dp/dt). A lowest mortality rate in the animals treated with the combination of both ACE inhibitor and AT(1) receptor antagonist was observed. Although lisinopril and losartan significantly decreased VW/BW ratio, when administered concomitantly, VW/BW ratio was lower than when either agent was administered individually. There were no differences in right ventricle hydroxyproline concentration. Only combination therapy decreased V0/BW ratio. The treatment with lisinopril plus losartan resulted in increases in the development of pressure versus untreated group; without alteration in dp/dt and -dp/dt.

CONCLUSIONS

The combination of the AT(1) receptor blockade and ACE inhibitor is more effective than individual treatment on ventricular remodeling and survival after MI in rats.

ET-1 in the myocardial interstitium: relation to myocyte ECE activity and expression

Increased plasma levels of endothelin-1 (ET-1) have been identified in congestive heart failure (CHF), but local myocardial interstitial ET-1 levels and the relation to determinants of ET-1 synthesis remain to be defined. Accordingly, myocardial interstitial ET-1 levels and myocyte endothelin-converting enzyme (ECE)-1 activity and expression with the development of CHF were examined. Pigs were instrumented with a microdialysis system to measure myocardial interstitial ET-1 levels with pacing CHF (240 beats/min, 3 wk; n = 9) and in controls (n = 14). Plasma ET-1 was increased with CHF (15 +/- 1 vs. 9 +/- 1 fmol/ml, P < 0.05) as was total myocardial ET-1 content (90 +/- 15 vs. 35 +/- 5 fmol/g, P < 0.05). Paradoxically, myocardial interstitial ET-1 was decreased in CHF (32 +/- 4 vs. 21 +/- 2 fmol/ml, P < 0.05), which indicated increased ET-1 uptake by the left ventricular (LV) myocardium with CHF. In isolated LV myocyte preparations, ECE-1 activity was increased by twofold with CHF (P < 0.05). In LV myocytes, both ECE-1a and ECE-1c mRNAs were detected, and ECE-1a expression was upregulated fivefold in CHF myocytes (P < 0.05). In conclusion, this study demonstrated compartmentalization of ET-1 in the myocardial interstitium and enhanced ET-1 uptake with CHF. Thus a local ET-1 system exists at the level of the myocyte, and determinants of ET-1 biosynthesis are selectively regulated within this myocardial compartment in CHF.

Therapeutic implications of escape from angiotensin-converting enzyme inhibition in patients with chronic heart failure

The level of inhibition of the angiotensin-converting enzyme (ACE) provided by standard doses of ACE inhibitors may only be partial during long-term treatment in patients with severe chronic heart failure (CHF). Partial ACE inhibition with time is often referred to as escape from ACE inhibition and labeled ACE escape. Several lines of evidence suggest that ACE escape occurs in patients with severe CHF. Plasma levels of angiotensin II rise above initial values during long-term ACE inhibition, and the effects of ACE inhibitors on cardiac remodeling and lowering of sympathetic nervous system activity attenuate after 1 year of treatment. Moreover, angiotensin II type I receptor blockade (ARB) produces clinical and hemodynamic benefits in patients with CHF who are already receiving ACE inhibitors. The therapeutic implications of ACE escape include evaluation of higher- than-standard doses of ACE inhibitors and routine addition of ARB to ACE inhibition in patients with severe CHF. Data are reviewed to demonstrate that ACE escape reflects inadequate ACE dosage rather than a decrease in ACE inhibition occurring with time.

Cardiac protection: evolving role of angiotensin receptor blockers

Congestive heart failure (HF) is a common and serious public health problem affecting approximately 5 million Americans. Recent treatment strategies have focused on attenuating the effects of angiotensin (Ang) II, which include vasoconstriction, sodium retention, sympathetic activation, and cell growth. Angiotensin-converting enzyme (ACE) inhibitors, which primarily block the systemic formation of Ang II, reduce HF-related morbidity and mortality rates. However, ACE inhibitors may not suppress Ang II activity over their entire dosing interval and, with long-term therapy, Ang II levels tend to return to normal. It is now known that Ang II can be formed independent of ACE by the action of enzymes such as chymase in local tissues, including the heart. Despite the established benefits of ACE inhibitor treatment, HF-related morbidity and mortality rates continue to increase because the aging of the population is placing more patients at risk of HF. By acting at the receptor level, Ang II receptor blockers (ARBs) should, at least theoretically, provide more "complete" Ang II blockade. Early evidence suggests that ARBs induce hemodynamic improvement in patients with HF and may reduce mortality rates. Because ACE inhibitors and ARBs block Ang II through fundamentally different mechanisms, the combination may provide additive therapeutic effects in patients with HF. Results from a pilot study suggest that the combination of an ACE inhibitor and valsartan results in a more thorough inhibition of Ang II and an additive improvement in cardiac hemodynamics. Clinical trials now in progress will elucidate the effects of combined ACE inhibitor and ARB therapy on HF-related morbidity and mortality rates.

Angiotensin II receptor blockers: review of the binding characteristics

Several angiotensin II receptor blockers (ARBs), including candesartan cilexetil, irbesartan, losartan, telmisartan, and valsartan, are currently approved by the US Food and Drug Administration (FDA) for the treatment of patients with hypertension. These agents share a common mechanism of action-antagonism of the angiotensin type 1 (AT1) receptor-and as a result, they block a number of angiotensin II effects that are relevant to the pathophysiology of cardiovascular disease, including vasoconstriction, renal sodium reabsorption, aldosterone and vasopressin secretion, sympathetic activation, and vascular and cardiac hyperplasia and hypertrophy. Unlike the angiotensin converting enzyme (ACE) inhibitors, these new drugs block the effects of angiotensin II regardless of whether it is produced systemically in the circulation or locally via ACE- or non-ACE-dependent pathways in tissues. ARBs also block the angiotensin II-induced feedback regulation of renin release, resulting in an increase in angiotensin II levels. With the AT1 receptor blocked, angiotensin II is available to activate the angiotensin type 2 (AT2) receptor, which mediates several potentially beneficial effects in the cardiovascular system, including vasodilation, antiproliferation, and apoptosis. Thus, ARBs provide a highly selective approach for regulating the effects of angiotensin II.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists in the treatment of heart failure caused by left ventricular systolic dysfunction

Activation of the renin-angiotensin-aldosterone system (RAAS) in left ventricular systolic dysfunction is a critically important determinant in the pathophysiologic processes that lead to progression of heart failure and sudden death. Angiotensin II, acting at the specific angiotensin receptor (AT1-R), activates a series of intracellular signaling sequences which are ultimately expressed within the cardiovascular system as vasoconstriction and associated vascular hypertrophy and remodeling. Angiotensin converting enzyme (ACE) inhibition leads to increases in the vasodilatory peptides bradykinin and substance P and at least an initial reduction in angiotensin II concentrations. AT1-R blocking drugs prevent access of angiotensin II to the AT1-R and thus prevent cellular activation. ACE inhibitors have clearly been demonstrated through a large number of clinical trials to increase survival in congestive heart failure, primarily by reducing the rate of progression of left ventricular dilatation and decompensation. However, this beneficial effect diminishes over time. Preliminary short-term clinical studies evaluating the efficacy of AT1-R blocking drugs in the treatment of heart failure have suggested that they elicit similar hemodynamic and neuroendocrine effects as do the ACE inhibitors. The combination ACE inhibitors and AT1-R blocking drugs offer the theoretical advantage of increasing bradykinin while blocking the actions of angiotensin II, and thus possibly show a synergistic effect. Again, preliminary studies have yielded encouraging results that are difficult to interpret because neither ACE inhibitor nor the AT1-R blocking drug doses were titrated to tolerance. Pharmacological manipulation of the RAAS has led to better understanding of its role in heart failure and improved clinical outcomes.