Angiotensin and the remodelling of the myocardium

Macro- and micromechanical remodelling in the fish atrium is associated with regulation of collagen 1 alpha 3 chain expression

Numerous pathologies lead to remodelling of the mammalian ventricle, often associated with fibrosis. Recent work in fish has shown that fibrotic remodelling of the ventricle is 'reversible', changing seasonally as temperature-induced changes in blood viscosity alter haemodynamic load on the heart. The atrial response to varying haemodynamic load is less understood in mammals and completely unexplored in non-mammalian vertebrates. To investigate atrial remodelling, rainbow trout were chronically cooled (from 10 ± 1 to 5 ± 1 °C) and chronically warmed (from 10 ± 1 to 18 ± 1 °C) for a minimum of 8 weeks. We assessed the functional effects on compliance using ex vivo heart preparations and atomic force microscopy nano-indentation and found chronic cold increased passive stiffness of the whole atrium and micromechanical stiffness of tissue sections. We then performed histological, biochemical and molecular assays to probe the mechanisms underlying functional remodelling of the atrial tissue. We found cooling resulted in collagen deposition which was associated with an upregulation of collagen-promoting genes, including the fish-specific collagen I alpha 3 chain, and a reduction in gelatinase activity of collagen-degrading matrix metalloproteinases (MMPs). Finally, we found that cooling reduced mRNA expression of cardiac growth factors and hypertrophic markers. Following long-term warming, there was an opposing response to that seen with cooling; however, these changes were more moderate. Our findings suggest that chronic cooling causes atrial dilation and increased myocardial stiffness in trout atria analogous to pathological states defined by changes in preload or afterload of the mammalian atria. The reversal of this phenotype following chronic warming is particularly interesting as it suggests that typically pathological features of mammalian atrial remodelling may oscillate seasonally in the fish, revealing a more dynamic and plastic atrial remodelling response.

Temperature-induced cardiac remodelling in fish

Thermal acclimation causes the heart of some fish species to undergo significant remodelling. This includes changes in electrical activity, energy utilization and structural properties at the gross and molecular level of organization. The purpose of this Review is to summarize the current state of knowledge of temperature-induced structural remodelling in the fish ventricle across different levels of biological organization, and to examine how such changes result in the modification of the functional properties of the heart. The structural remodelling response is thought to be responsible for changes in cardiac stiffness, the Ca²⁺ sensitivity of force generation and the rate of force generation by the heart. Such changes to both active and passive properties help to compensate for the loss of cardiac function caused by a decrease in physiological temperature. Hence, temperature-induced cardiac remodelling is common in fish that remain active following seasonal decreases in temperature. This Review is organized around the ventricular phases of the cardiac cycle – specifically diastolic filling, isovolumic pressure generation and ejection – so that the consequences of remodelling can be fully described. We also compare the thermal acclimation-associated modifications of the fish ventricle with those seen in the mammalian ventricle in response to cardiac pathologies and exercise. Finally, we consider how the plasticity of the fish heart may be relevant to survival in a climate change context, where seasonal temperature changes could become more extreme and variable.

Summary: Thermal acclimation of some temperate fishes causes extensive remodelling of the heart. The resultant changes to the active and passive properties of the heart represent a highly integrated phenotypic response.

A potential role for angiotensin II in obesity induced cardiac hypertrophy and ischaemic/reperfusion injury

BACKGROUND

The mechanisms for obesity induced myocardial remodelling and subsequent mechanical dysfunction are poorly understood. There is good evidence that angiotensin II and TNFalpha have strong growth promoting properties and are elevated with obesity. In addition, these two peptides may interact to exacerbate myocardial ischaemic/reperfusion injury.

HYPOTHESIS

Obesity increases systemic and myocardial renin-angiotensin system (RAS) activity and TNFalpha levels and contributes to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

METHODS

Male Wistar rats were placed on a standard rat chow diet or cafeteria diet for 16 weeks. Two additional groups of rats received the respective diets and losartan (30 mg/ kg/d) in their drinking water. Hearts were perfused on the isolated working rat heart perfusion system and mechanical function was documented before and after 15 min normothermic total global ischaemia. Blood and myocardial samples were collected for angiotensin II, TNFalpha and NADPH oxidase activity determinations.

RESULTS

The rats on the cafeteria diet became obese compared to rats on the standard rat chow (438 +/- 5.9 g vs 393 +/- 7.3 g for control, p < 0.05). Obesity was associated with elevated serum angiotensin II (0.050 +/- 0.015 pmol/ml vs. 0.035 +/- 0.003 pmol/ml, p < 0.05) and TNFalpha levels (42.8 +/- 5.93 pg/ml vs. 13.18 +/- 2.50 pg/ml, p < 0.05), and increased heart to body weight ratios (3.1 +/- 0.04 mg/g vs. 2.8 +/- 0.03 mg/g, p < 0.05). Losartan had no effect on body weight but decreased basal myocardial angiotensin II and TNFAlpha levels as well as heart to body weight ratio in the obese and lean controls (2.5 +/- 0.05 mg/g and 2.6 +/- 0.04 mg/g relative to their controls, p < 0.05). Hearts from obese rats had lower reperfusion aortic outputs (AO) than their concurrent controls (18.42 +/- 1.17 ml/min vs. 27.8 +/- 0.83 ml/min, p < 0.05). Losartan improved aortic output recoveries in obese rats (23.0 +/- 1.71 ml/min, p < 0.05).

CONCLUSIONS

Obesity increased serum angiotensin II and TNFalpha levels, blood pressure, and heart weight to body weight ratios. These changes were associated with decreased basal and post-ischaemic myocardial mechanical function. Chronic AT(1) receptor antagonism prevented the adverse changes in heart weight, mechanical function and susceptibility to ischaemic/reperfusion injury. Although current data do not exclude additional mechanisms for obesity induced cardiac remodelling, they suggest that angiotensin II may contribute to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

Tonin in rat heart with experimental hypertrophy

The present study was undertaken to determine tonin expression and activity in rat heart presenting isoproterenol-induced hypertrophy. Renin, angiotensin-converting enzyme (ACE), and angiotensinogen (AG) expression were also determined. Wistar rats were treated with isoproterenol for 7 days (5 mg x kg(-1) x day(-1) sc). For untreated animals, the levels of tonin-specific activity in the atrium were 2.6- and 5.5-fold higher than those of the left and right ventricle, respectively. After treatment, the levels of tonin-specific activity increased twofold in the atrium but did not change in the ventricles. Renin expression was not detectable in these structures, and ACE expression levels did not change with treatment. AG expression was detected in the left ventricle at very low levels compared with the atrium and increased significantly only in the hypertrophied atrium (1.8-fold). Tonin mRNA was not detected in the ventricle but was found at low levels in the atrium, which increased after isoproterenol treatment. Our results permit us to conclude that tonin may play a role in the process of heart hypertrophy in the rat.

Effects of angiotensin II type 1 receptor antagonist, YM358, on cardiac hypertrophy and dysfunction after myocardial infarction in rats

This study was undertaken to investigate the effects of an angiotensin II type 1 receptor antagonist, YM358 (2,7-diethyl-5-[[2'(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-5H-pyrazolo [1,5-b] [1,2,4]triazole potassium salt monohydrate), on cardiac hypertrophy and dysfunction in rats with heart failure after myocardial infarction (MI). One day after the coronary ligation, rats were randomized, and administered YM358 or vehicle for 2, 4 or 8 weeks. In MI rats, mean blood pressure, left ventricular (LV) systolic pressure, and the first derivative of LV pressure significantly decreased, and LV end-diastolic pressure (LVEDP) markedly increased after 2 to 8 week treatment of YM358. From 2 weeks after the ligation, ratios of cardiac weight and lung weight to body weight (BW) significantly increased, which indicated the progression of cardiac hypertrophy and lung congestion in MI rats. Two weeks after the ligation, YM358 did not improve LV function, although it decreased the elevated LVEDP and cardiac weights/BW ratios 8 weeks after the ligation. These results indicated that long-term treatment with YM358 improves the reduced cardiac function and reduces cardiac hypertrophy after MI, and may be useful for the treatment of congestive heart failure.

Increased expression of biglycan mRNA in pressure-overloaded rat heart

Biglycan mRNA expression in rat myocardium after abdominal aortic banding with renal ischemia was examined. The Northern blot analysis demonstrated that expression of biglycan mRNA in the pressure-overloaded hearts on days 2, 7, 14 and 28 was 2.88 +/- 0.89, 2.32 +/- 0.49, 2.17 +/- 0.57 and 1.81 +/- 0.46-fold higher, respectively, than that in the sham-operated hearts. In situ hybridization showed an increased density of biglycan mRNA signal-positive cells in the pressure-overloaded hearts. The cells with positive signals were spindle-shaped mesenchymal cells in the myocardial interstitium. A marked increase in biglycan mRNA signal expression was also observed in endothelial cells and smooth muscle cells of the thickened myocardial capillary wall. These results demonstrated an increase in biglycan mRNA in the pressure-overloaded heart in mesenchymal cells in the myocardial interstitium, and in endothelial and smooth muscle cells of the capillaries, indicating that biglycan contributes to the ventricular and vascular remodeling in response to pressure overload.

In-hospital heart failure, first-year ventricular dilatation and 10-year survival after acute myocardial infarction

BACKGROUND

Little is known about the factors that determine long-term prognosis in patients who have survived the first year after acute myocardial infarction (AMI).

AIMS

To study the influence of left and right ventricular (LV and RV) dilatation during the first year after AMI on subsequent 10-year survival in comparison with in-hospital heart failure and other established prognostic indices.

METHODS

Radionuclide ventriculography was performed before the era of thrombolysis and post-infarction ACE-inhibition in 57 patients with AMI at hospital discharge and again 1 year later, and compared with survival the ensuing 10 years.

RESULTS

After 1 year significant LV-dilatation (>20%) had occurred in 32 (56%) patients. One year after the re-investigation the mortality in these was 19% vs. 0% in patients without dilatation (P=0.02); after 5 years the difference was 38 vs. 12% (P=0.02), whereafter it declined and became insignificant at 10 years. Neither RV-dilatation, nor LVEF determined at discharge or at the 1-year reinvestigation influenced long-term survival. In contrast, clinical heart failure recorded during the hospital stay had a sustained negative influence on long-term survival.

CONCLUSION

Progressive LV dilatation after discharge and clinical heart failure during the hospital stay are both determinants of late survival after AMI, whereas LV ejection fraction at hospital discharge or 1 year later has little, if any, effect on survival beyond 1-year post-AMI.

Correlation between changes in morphology, electrical properties, and angiotensin-converting enzyme activity in the failing heart

Evidence is available that morphologic and electrophysiologic abnormalities are present in the failing heart. In the present work, the progressive changes in electrical properties and morphology of the failing heart of Syrian cardiomyopathic hamsters (TO2) were investigated at different stages of the pathological process, and the possible role of the renin-angiotensin system was studied. Cardiomyopathic hamsters 2 and 11 months of age were used. Age-matched normal hamsters (F1B) were utilized as controls. Measurements of membrane potential, conduction velocity and refractoriness were made with conventional intracellular electrodes connected to a high impedance DC amplifier. Serum and cardiac angiotensin-converting enzyme (ACE) activities were measured in controls and cardiomyopathic animals. The results indicated that interstitial fibrosis and calcification were present in the heart of 2-month old Syrian cardiomyopathic hamsters. Measurements of the resting potential performed in the isolated right ventricle of 2-month old Syrian cardiomyopathic hamsters indicated an average value of -66.7 +/- 0.96 mV (n = 25); in the controls of the same age was -78.5 +/- 1 mV (n = 25, P < 0.05); and in 11-month old cardiomyopathic hamsters was -67.8 +/- 0.83 mV (n = 10). The duration of the action potential measured at 50 and 90% of repolarization in 2-month old hamsters was well above the controls. The conduction velocity measured in the isolated right ventricle of 2-month old Syrian cardiomyopathic hamsters (44.2 +/- 1.6 cm/s, n = 12) was not different from the control (43.7 +/- 1.1 cm/s, n = 7, P > 0.05) but was significantly larger than that recorded from the ventricle of 11-month old animals (37.8 +/- 2.9 cm/s, n = 11, P < 0.05). ACE activity was 0.26 +/- 0.01 nmol/mg x min in the heart of controls at 2 months of age and did not change with age. Although in the 2-month old cardiomyopathic hamsters the enzyme activity (0.28 +/- 0.04 nmol/mg x min) was not different from the controls (P > 0.05), in myopathic animals at 11 months of age, the enzyme activity (0.56 +/- 0.027 nmol/mg x min) was greater than controls (P < 0.05). The ACE activity in plasma followed the same pattern. The conclusion from these experiments is, that some parameters like resting potential, action potential duration, and morphological abnormalities appeared quite early in the failing process. The decline in conduction velocity, however, appeared later on, concurrently with the activation of plasma and cardiac renin-angiotensin systems.

Rationale and design of the Valsartan Heart Failure Trial: a large multinational trial to assess the effects of valsartan, an angiotensin-receptor blocker, on morbidity and mortality in chronic congestive heart failure

BACKGROUND

To investigate the role of persistent angiotensin activity despite angiotensin-converting enzyme inhibitor therapy in the progression of heart failure, the Valsartan Heart Failure Trial has been designed to investigate the effect of the angiotensin-receptor blocker, valsartan, on morbidity and mortality.

METHODS AND RESULTS

Nearly 5,000 patients with New York Heart Association classes II to IV heart failure, while receiving all standard therapy, are being randomized to treatment with valsartan, 160 mg twice daily, or placebo in a worldwide study. Follow-up will be continued until 906 deaths have been recorded. Additional end points will include the need for hospitalization, other major morbid events, quality--of life measurement, changes in neurohormone levels, and changes in left ventricular size and function. Substudies will explore exercise tolerance, arrhythmias, and magnetic resonance imaging.

CONCLUSION

This study should help establish the role of angiotensin-receptor blockade in the treatment of heart failure.

Effect of chronic blockade of angiotensin II-receptor subtypes on aortic compliance in rats with myocardial infarction

This study was undertaken to investigate changes in aortic geometry and compliance after long-term blockade of angiotensin receptors type 1 (AT1) and AT2 receptors under basal conditions and after myocardial infarction (MI). Sham-operated (sham) or MI rats received either no treatment, AT1 antagonist GR138950C (GR; 2 mg/kg/day i.v.), or AT2 antagonist PD123319 (PD; 3 mg/kg/day s.c.). After 3 weeks, mean arterial blood pressure (MAP) was measured. Thoracic aorta diastolic diameter (D[dia]), compliance coefficient (CC), and distensibility coefficient (DC) were determined noninvasively in anesthetized rats by using ultrasound and wall tracking. After the rats were killed, histologic measurements were made on aortic cross sections. In sham rats, MAP was reduced by GR treatment (76 +/- 6 vs. 106 +/- 5 mm Hg), but not by PD. D(dia) was reduced in both GR-treated (1.74 +/- 0.08 vs. 2.09 +/- 0.05 mm) and PD-treated (1.83 +/- 0.05 vs. 2.09 +/- 0.05 mm) sham rats. CC and DC were not modified by either treatment. Although media cross-sectional area was not affected by either GR or PD treatment in sham rats, media thickness and media/lumen ratio were increased in both cases. Induction of MI had no effect on aortic structure, geometry, or mechanics; however, treatment with either GR or PD improved DC versus untreated MI rats. We conclude that AT1 and AT2 receptors are involved in angiotensin II-mediated effects on aortic geometry and mechanics under both basal conditions and after MI. Whereas blockade of AT1 receptors most likely influences vascular properties through a depressor mechanism, AT2 receptors induce pressure-independent remodeling.

Prolonged Captopril Therapy in Murine Viral Myocarditis

BACKGROUND: Acute myocarditis can progress to chronic heart muscle disease and cardiomyopathy. In the coxsackievirus B(3) (CB(3)) mouse model of myocarditis, early administration of captopril, an angiotensin-converting enzyme (ACE) inhibitor, ameliorated histopathological changes in inflammation, necrosis, and calcification and reduced heart weight. Late administration of captopril reduced heart weight but did not affect the histological findings. In this study, we investigated the effects of prolonged captopril treatment in the chronic phase of this model. METHODS AND RESULTS: Three-week-old male CD(1) mice were infected with CB(3) and then randomized to receive placebo or captopril starting on day 7 of infection. Captopril, 2 g/L, was given as the drinking water daily for up to 6 months. Autopsies were performed at 6 and 10 months. Heart-to-body weight ratios were obtained, and deaths were tallied. Myocardial fibrosis was graded according to a score system. In addition, picrosirius red stain (PSR) also was used for assessment of collagen deposition. Mean heart weights were similar in both groups. Mean body weight was significantly lower in captopril-treated mice (40.7 g) than in the untreated group (43.6 g) at 6 months (P =.0155), and mortality was higher (8.7 vs 0.87%; P =.009). At 6 months, the mean myocardial fibrosis score in treated mice (0.12) was significantly less than in untreated animals (0.35; P =.035). With PSR, the mean myocardial fibrosis score in the captopril group (1.20) was also significantly less than in the untreated group (1.58; P =.045). At 10 months, fibrosis scores were similar in both groups. CONCLUSIONS: Chronic captopril treatment in CB(3) myocarditis reduces myocardial fibrosis.

Electrophysiologic and morphologic abnormalities in the failing heart: effect of enalapril on the electrical properties

BACKGROUND

Knowledge of the electrophysiologic abnormalities in the failing heart is meager. In this work morphologic and electrophysiologic changes were investigated in the cardiomyopathic hamster (BIO TO-2) at 11 months of age. The results were compared with control hamsters (F1B) of the same age.

METHODS AND RESULTS

Conventional KCl microelectrodes were used to measure membrane potential, conduction velocity, and refractoriness. Histologic studies consisted of Harris' hematoxylin and eosin, Masson trichrome, and von Kossa's calcium stain. The resting potential of myopathic fibers (-67.8 mV; SEM 1 0.83) in the cardiomyopathic hamsters was less negative than the control subjects' potential (-78.5 V; SEM + 1), and the action potential duration measured at 50% of repolarization was increased by 213%. The conduction velocity (36.9 cm/s) was 15.7% lower than that of the control subjects. Enalapril (50 micrograms/mL) caused a hyperpolarization of 6.8 mV, it increased the action potential duration at 90% of repolarization by 110%, and the conduction velocity of the myopathic fibers was appreciably increased compared to the control hamsters'. The refractoriness of myopathic and normal ventricular fibers was also increased by enalapril. Histologic studies performed on the right and left ventricular wall indicated interstitial fibrosis, necrotic foci, and extensive calcification.

CONCLUSIONS

The results indicate severe morphologic and electrophysiologic abnormalities in the failing ventricular muscle. The effect of enalapril on membrane potential and conduction velocity might indicate that the activation of the cardiac renin-angiotensin system during the process of heart failure is, in part, responsible for the abnormalities described here. The improvement of impulse propagation and the increase in refractoriness seem to represent important factors involved in the antiarrhythmic action of enalapril.

Nipradilol, a new beta-adrenergic blocker, reduces left ventricular remodeling following myocardial infarction in spontaneously hypertensive rats

Left ventricular (LV) cavity dilation (remodeling) following myocardial infarction (MI) is a risk factor for morbidity and mortality. This study was undertaken to determine whether nipradilol, a new beta-adrenergic blocker with vasodilating action, reduces LV remodeling after MI produced by coronary ligation in spontaneously hypertensive rats. The effects on LV remodeling of the following drugs, which were administered orally for 4 weeks, were evaluated by assessing LV end-diastolic volume index (LVEDVI): (1) vehicle, (2) nipradilol, 10 mg/kg per day. (3) propranolol, 50 mg/kg per day, and (4) captopril, 30 mg/kg per day. Since LVEDVI depends on infarct size, the effects of the drugs on LVEDVI were compared between rats with a similar infarct size, i.e., moderate, 20%-40%; and large, 40%-60%, on the basis of the histological determination of infarct size. The nipradilol-treated and captopril-treated rats had significantly smaller LVEDVI than did the vehicle-treated rats with both moderate and large infarction (large infarct: 2.48 +/- 0.12 ml/kg for the vehicle group, 1.69 +/- 0.10 ml/kg for the nipradilol group, P < 0.01, and 1.79 +/- 0.14 ml/kg for the captopril group, P < 0.01). In contrast, LVEDVI-in the propranolol-treated rats was significantly greater than that in the vehicle-treated rats with a moderate infarct (2.09 +/- 0.09 ml/kg for the vehicle group versus 2.44 +/- 0.10 ml/kg for the propranolol group, P < 0.05). The results indicate that nipradilol and captopril reduce LV remodeling after MI, whereas propranolol promotes it.

Cardioprotective effect of angiotensin-converting enzyme inhibitors in patients with coronary artery disease

Clinical and experiments study with angiotensin-converting enzyme (ACE) inhibitors suggest that these agents may improve coronary artery disease by acting at multiple sites in the series of events leading to end-stage heart disease. These agents reduce blood pressure, improve prognosis and symptoms in patients with severe heart failure and in patients after acute myocardial infarction with left ventricular dysfunction. They are useful in the early, acute phase of myocardial infarction. More recently, ACE inhibitors have been shown to reduce in vitro vascular hypertrophy, to attenuate arteriosclerosis, and to maintain endothelium function. Whether these effects occur at clinical levels is still uncertain. The exciting clinical data have led to the proposal that alteration of ACE activity, particularly in tissue, is an important factor in development and progression of CAD. The ACE system is complex, with endocrine, paracrine, and autocrine effects. ACE is present in cardiac and vascular tissue. Therefore, the beneficial effects of ACE inhibitors can be classified as "cardio" and "vasculo" protective. This article summarizes a number of independent and complementary mechanisms pointing to a role of ACE and ACE inhibition in coronary artery disease.

Weight reduction regresses left ventricular mass regardless of blood pressure level in obese subjects

The effects of weight reduction on left ventricular mass in obese normotensive and hypertensive subjects were investigated. Previous studies have shown that weight reduction in hypertensive (HT) obese patients is associated with decreased left ventricular mass (LVM) and decreased blood pressure (BP). This study was performed to examine whether weight reduction would also regress LVM in normotensive (NT) obese subjects and to clarify the mechanisms of these effects if they occurred. A weight-reduction program consisted of mild exercise and mild hypocaloric intake. M-mode echocardiography was performed to estimate the LVM. After the 12-week intervention, the mean reductions in body weight (BW) in the NT (n = 11) and HT (n = 11) groups were 4.9 kg (p < 0.005) and 4.6 kg (p < 0.0005), respectively. Systolic, diastolic, and mean BP were significantly reduced by 13, 9, and 11 mm Hg, respectively, in the HT group. By contrast, no significant changes in systolic, diastolic, or mean BP were observed in the NT group. LVM was significantly reduced from 176 +/- 26 gm to 159 +/- 26 gm (p < 0.05) in the HT group and from 167 +/- 33 gm to 145 +/- 34 gm (p < 0.02) in the NT group. These results suggest that weight reduction in obese subjects by mild exercise and mild hypocaloric intake can lead to a reduction in LVM, regardless of whether the subjects have normal or high blood pressure.

The cellular basis of angiotensin converting enzyme mRNA expression in rat heart

Angiotensin converting enzyme (ACE) is a key factor in the regulation of two peptide systems: the renin angiotensin system (RAS) and the kinin-kallikrein system (KKS). Since it is involved in the biosynthesis of Angiotensin II (Ang II) as well as in the degradation of bradykinin (BK) it could play an important role in cardiovascular physiology and pathophysiology. ACE is widely expressed in the heart and upregulated in pathophysiological situations such as heart failure and cardiac hypertrophy. In addition, inhibition of ACE has beneficial effects in these conditions. Whereas the regulation of cardiac ACE has been studied extensively, little is known concerning the cellular expression of ACE in cardiac tissue. To define the cellular localization of ACE mRNA expression in the rat heart, we separated coronary microvascular endothelial cells from cardiac myocytes using differential centrifugation and growth on selective media. ACE mRNA expression was measured by a specific polymerase chain reaction assay after reverse transcription (RT-PCR) in different cardiac cells. The studies showed that ACE is differentially expressed in endothelial cells as well as in cardiac myocytes. This differential regulation of ACE in myocytes and non-myocytes may play a role for the diverse actions of the cardiac angiotensin system under physiological and pathological conditions.

Effects of enalapril on T and B cell function in rats after myocardial infarction

The cellular mechanisms following myocardial infarction remain poorly characterized. It is believed that an inflammatory and immunologic process may be involved and that the beneficial effects of enalapril on remodeling may, in part, work through an immune mechanism. To characterize the effect of enalapril on immune alterations in the late phase of ventricular remodeling after myocardial infarction, rats underwent left coronary artery ligation followed by 6 weeks of either enalapril or placebo treatment. Infarct sizes, heart weights, and volumes were compared. Peripheral and splenic leukocyte and lymphocyte subsets, along with T cell blastogenesis, were quantified in enalapril treated rats 6 weeks after coronary ligation and compared to untreated control rats. Additionally, antibody production to a de novo antigen, keyhole limpet hemocyanin, was assessed with and without treatment. Average infarct size was equivalent among enalapril-treated myocardial infarction rats and untreated infarct rats. There was, however, less left and right ventricular hypertrophy in the enalapril treated group. Enalapril completely prevented the 42% increase in white blood count, the 88% increase in neutrophils, and the 28% increase in lymphocyte count seen in untreated infarct rats. Both untreated and enalapril treated rats tended toward a decrease in T helper:suppressor ratio. All rats treated with enalapril, however, had a significant increase in the T helper:suppressor ratio versus untreated control rats (F = 3.6, P = .018). Blastogenesis was markedly increased in T cells from infarcted animals. This was mitigated by treatment with enalapril. Additionally, immunoglobulin G antibody production was significantly lessened in rats treated with enalapril. The results of this study suggest that alterations in immunoregulatory cell type and function occurs following myocardial infarction. The beneficial effects of the angiotensin-converting enzyme inhibitor enalapril may be, in part, due to its mitigating effects on immune cell release and activation following myocardial infarction.

Defining the susceptible period of developmental toxicity for the AT1-selective angiotensin II receptor antagonist losartan in rats

Previous developmental and reproductive toxicity studies conducted in rats with Losartan, a potent AT1 subtype selective angiotensin II receptor antagonist, noted treatment-related effects on the pups of dams treated beyond the second trimester through lactation, as demonstrated by increases in pre- and postweaning pup deaths and decreased pup body weights [Spence et al. (1995) Teratology 51:000-000]. The studies presented here were designed to define the critical period for the induction of neonatal toxicity and to examine the effects of Losartan on kidney development when the drug is administered to the dam beyond the second trimester through lactation. In a developmental toxicity study with postweaning evaluation, pregnant rats were administered 5, 20, and 100 mg Losartan/kg/day on gestation days 6 through 15 (GD 6-15). There were no adverse effects on the F1 generation as assessed by mortality, clinical signs, weight gain, external examinations, developmental signs, behavioral tests, and gross or microscopic examination of the kidney. In a fostering/cross-fostering study, pregnant rats were administered 100 mg Losartan/kg/day on GD 15 through lactation day 20 (LD 20). Following delivery, pups from dams treated with Losartan were fostered to control dams, pups from control dams were fostered to Losartan-treated dams, and pups were also fostered to dams within the same group. Maternal exposure to Losartan during lactation increased the incidence of pup deaths on postnatal days 1-3 (PND 1-3), caused decreased pup weights on PND 7, and decreased performance in the auditory startle test in females and increased performance on the second swim maze test in males, relative to controls. Maternal exposure to Losartan during gestation was associated with decreased pup weight on PND 21 and effects observed on male performance in the swim maze test. Treatment during gestation was also associated with decreased pup cardiac weight as well as drug-induced histopathological changes of the kidneys from F1 pups, including medial hypertrophy of intracortical arterioles and dilatation of the renal pelvis. While the cardiac and renal vascular effects disappeared with time, significant renal lesions were still evident by PND 90. In a late-gestation/lactation study with renal evaluation, pregnant rats were administered 0.5, 1.0, 5.0, 20, and 100 mg Losartan/kg/day on GD 15-LD 20. Maternal toxicity was evident as decreased body weight gain in the 100 mg Losartan/kg/day group.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibition and beta-adrenoceptor blockade regress established ventricular remodeling in a canine model of discrete myocardial damage

OBJECTIVES

This study was designed to assess the effect of angiotensin-converting enzyme inhibition and beta-adrenoreceptor blockade on established ventricular remodeling.

BACKGROUND

Angiotensin-converting enzyme inhibitor therapy attenuates the development of ventricular remodeling when given shortly after myocardial infarction. However, regression of established ventricular remodeling after infarction has received little attention.

METHODS

The relative effects of angiotensin-converting enzyme inhibitor therapy and beta-adrenoceptor blockade on established ventricular remodeling were assessed in a canine model characterized by increased left ventricular mass and chamber dilation as a result of localized myocardial necrosis produced by transmyocardial direct current shock. Dogs were randomly assigned to 3 months of therapy with captopril (25 mg twice daily, n = 7) or metoprolol (100 mg twice daily, n = 7) or to a control group with no intervention (n = 6), 11 +/- 4 (mean +/- SD) months after acute myocardial damage.

RESULTS

Compared with the control group, dogs in both the captopril and metoprolol groups had reduced left ventricular mass as measured by magnetic resonance imaging (-8.1 +/- 3.8 vs. 1.7 +/- 2.8 g, p = 0.003 and -9.6 +/- 5.6 vs. 1.7 +/- 2.8 g, p = 0.001), respectively. Captopril and metoprolol also produced a reduction in left ventricular end-diastolic volume (-7.6 +/- 6.0 and -6.0 +/- 5.8 ml, respectively) compared with the control value (-1.6 +/- 3.8 ml) (p = 0.14 [NS]). Both agents reduced mean arterial pressure but had disparate effects on pulmonary wedge pressure and right atrial pressure. There was no significant correlation between change in ventricular mass or volume and change in any measured hemodynamic or neurohormonal variable.

CONCLUSIONS

These data suggest that pharmacologic intervention with angiotensin-converting enzyme inhibition or beta-adrenoceptor blockade can result in regression of established ventricular remodeling. The mechanism of this response will require further study, but these data did not support a close association between regression of remodeling and hemodynamic unloading of the ventricle or systemic neuroendocrine factors.

Relative effects of alpha 1-adrenoceptor blockade, converting enzyme inhibitor therapy, and angiotensin II subtype 1 receptor blockade on ventricular remodeling in the dog

BACKGROUND

Progressive ventricular remodeling after myocardial damage is associated with a poor prognosis. Optimal prevention of the histopathological processes involved in remodeling requires a more complete understanding of the mechanisms involved in initiating and maintaining these structural changes. Since the sympathetic nervous system and the renin-angiotensin system may be involved in the remodeling process, the structural effects of pharmacological inhibitors have been evaluated in a canine model of localized myocardial injury resulting from transmyocardial DC shock.

METHODS AND RESULTS

The study is comprised of two protocols run in series. In protocol 1, zofenopril (Z), a converting enzyme inhibitor (CEI), prevented the increase in left ventricular mass (LVM) and end-diastolic volume (LVV) observed in the control group (C) at 16 weeks (Z: LVM, 69.8 +/- 3.4 to 65.4 +/- 2.6 g, P = NS; LVV, 45.4 +/- 2.7 to 51.6 +/- 2.7 mL, P = NS; C: LVM, 68.4 +/- 3.2 to 91.4 +/- 2.9 g, P = .0001; LVV, 56.6 +/- 3.0 to 71.9 +/- 2.4 mL, P = .0003). Terazosin, an alpha 1-adrenoceptor antagonist, failed to prevent remodeling at 16 weeks despite continued receptor blockade. In protocol 2, the antiremodeling effect of full-dose CEI therapy with ramipril was confirmed. Low-dose ramipril that exerted no hemodynamic effect failed to prevent remodeling (LVM, 89.7 +/- 4.6 to 105.7 +/- 3.4 g, P = .01; LVV, 61.8 +/- 3.8 to 76.8 +/- 3.3 mL, P = .002). An angiotensin II subtype 1 receptor blocker also failed to prevent the increase in LVM or LVV (LVM, 89.0 +/- 4.6 to 109.7 +/- 5.3 g, P = .0001; LVV, 66.0 +/- 1.9 to 78.4 +/- 3.6 mL, P = .007).

CONCLUSIONS

High-dose CEI therapy can prevent progressive structural changes resulting from localized myocardial damage induced by DC shock. the failure of alpha 1-adrenoceptor blockade and angiotensin II subtype 1 blockade to attenuate remodeling argues against an important direct role for norepinephrine acting through alpha 1-receptors or angiotensin II acting through the type 1 receptor in the remodeling process in this model.

Cellular mechanisms of captopril-induced matrix remodeling in Syrian hamster cardiomyopathy

BACKGROUND

Although angiotensin-converting enzyme (ACE) inhibitors have become a mainstay of treatment for chronic congestive heart failure (CHF), it is not known whether the cardiac remodeling effects are a secondary phenomenon, resulting from ACE inhibitors' hemodynamic actions of afterload reduction, or occur through an independent mechanism.

METHODS AND RESULTS

We used ultrasonic tissue characterization to define potentially salutary effects of treatment with ACE inhibitors on the material properties of the heart and its potential influence on cardiac remodeling at the cellular level. Ten 1-month-old, cardiomyopathic (CM) Syrian hamsters and 6 normal (NL) hamsters were treated with captopril (2 g/L water ad libitum), and 10 CM hamsters and 10 NL hamsters were maintained untreated for 3 months. Hearts were excised, and backscattered radiofrequency data were acquired from 1200 independent sites from each specimen with a high-resolution 50-MHz acoustic microscope for calculation of integrated backscatter (IB). Treatment with captopril reduced left ventricular mass, calcium concentration, and IB in CM hearts without affecting myofiber size or collagen concentration. The IB from grossly normal regions of myocardium in NL hamsters, treated CM hamsters, and untreated CM hamsters was not significantly different. The IB from the microscopic regions of scar tissue in treated CM hamsters was significantly less (P = .0004) than that from scar tissue in untreated CM hamsters.

CONCLUSIONS

The reduced IB from treated scar tissue components reflects specific alterations in the material properties (elastic stiffness, density) of fibrous regions in CM hearts induced by captopril. This is the first report that defines specific cellular effects of ACE inhibitors on the material properties of isolated components of cardiac tissue in experimental cardiomyopathy. These alterations in material properties of scar tissue components represent a potential mechanism for the salutary actions of ACE inhibitors in heart failure.

Dosing of ACE inhibitors in postinfarct protection

ACE inhibitors improve not only symptoms and signs of heart failure in patients with symptomatic left ventricular dysfunction but also lead to a slower progression of heart failure. In asymptomatic patients with left ventricular dysfunction, the progression to symptomatic heart failure is retarded by ACE inhibitors. As heart failure is preceded in about 80% by myocardial infarctions, trials were designed to influence the development of heart failure after myocardial infarction. It could be shown that therapy with ACE inhibitors ameliorates the progressive left ventricular dilatation and that this effect is translated into a significant increase of life expectancy. Mainly based on the CONSENSUS I study, large doses of ACE inhibitors were used in most subsequent trials. The mean daily doses of enalapril were 18.4 mg in the CONSENSUS I trial and 16.6 and 16.7 mg in both arms of the SOLVD trial. There is a trend towards lower doses of ACE inhibitors, as in the SAVE trial only 79% of the patients taking captopril received the target dose of 150 mg daily. Smaller studies used similar target doses, but a beneficial effect on left ventricular enlargement has been shown with a daily dose of only 75 mg captopril. Based on the hypothesis that the left ventricular enlargement is mainly determined by the activation of the local cardiac renin angiotensin system, even lower, and therefore better tolerated, doses of ACE inhibitors may prove effective. However, studies comparing the effect of different doses of ACE inhibitors on left ventricular remodeling are missing. Consequently, the above-mentioned target doses of ACE inhibitors should be aimed at when treating patients after myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of functional angiotensin II receptors on rat cardiac fibroblasts

BACKGROUND

Cardiac hypertrophy results in an increased deposition of the extracellular matrix (ECM) proteins fibronectin and collagen. Recent evidence indicates that angiotensin II (Ang II) might have an important role in the development of myocardial fibrosis accompanying cardiac hypertrophy. We sought to determine whether fibroblasts of cardiac origin (isolated from neonatal and adult animals) express receptors for Ang II and to examine the ability of this peptide to regulate fibronectin and collagen gene expression in a cultured adult cardiac fibroblast cell preparation.

METHODS AND RESULTS

Binding of 125I-Ang II to both neonatal and adult cardiac fibroblasts in culture was specific, reversible, and saturable, with the receptor evenly distributed over the cell population. Competition binding experiments with receptor-specific antagonists indicate that Ang II receptors found on both fibroblast types were of the AT1 subtype. Analysis of mRNA levels for the AT1 receptor indicates that adult cardiac fibroblasts express higher levels of the message than neonatal fibroblasts or cardiac myocytes. Addition of 10(-9) mol/L Ang II to adult cardiac fibroblasts resulted in an induction of ECM proteins above control levels, as determined through Northern blots and total collagen assays.

CONCLUSIONS

Results from this study indicate that neonatal and adult rat cardiac fibroblasts in culture express AT1 receptors for Ang II. Ang II stimulation of AT1 receptors results in an increased gene expression for ECM proteins. These data suggest that Ang II might have important regulatory roles over cardiac fibroblast function under normal and pathological conditions.

Long-term oral nitrate therapy prevents chronic ventricular remodeling in the dog

OBJECTIVES

The purpose of this experiment was to assess the long-term effects of oral nitrate therapy on ventricular remodeling in a canine model of discrete myocardial damage.

BACKGROUND

A progressive increase in left ventricular mass and volume has been documented after experimental and clinical myocardial infarction. This ventricular remodeling has been associated with the development of congestive heart failure. Nitrate therapy, especially when combined with hydralazine, is effective in the management of clinical heart failure. Moreover, nitrates inhibit infarct expansion, one of the earliest manifestations of ventricular remodeling. Whether nitrates can attenuate chronic left ventricular remodeling is unknown.

METHODS

Dogs with discrete myocardial necrosis produced 24 h earlier by transmyocardial direct current shock were randomized to receive isosorbide mononitrate, 30 mg twice daily (n = 10), or no treatment (n = 4); the latter group was augmented by 13 control dogs from a prior study in which an identical protocol was used. Ventricular structure was assessed with nuclear magnetic resonance imaging at baseline and at 1 and 16 weeks after myocardial damage.

RESULTS

Left ventricular mass increased at 1 week in the control group (mean +/- SD 68.1 +/- 10.7 g to 80.1 +/- 12.1 g, p = 0.0001) but not in the nitrate-treated group (70.2 +/- 7.7 g to 69.6 +/- 7.3 g, p = NS). No change in left ventricular volume was observed in either group during the 1st week after myocardial damage. After 16 weeks of follow-up left ventricular mass had increased by 12.7 +/- 7.1 g (p = 0.001) in the control group and had decreased by 1.2 +/- 7.7 g in the nitrate group. Left ventricular volume was increased at 16 weeks by 14.2 +/- 10.3 ml in the control group but was decreased by 3.7 +/- 7.5 ml in the nitrate group. Isosorbide mononitrate produced transient hemodynamic effects with a return of most measured variables toward baseline within 2 h after administration of the drug. At 1 week there was no intergroup difference in rest hemodynamic variables assessed 12 h after drug administration. At 16 weeks, pulmonary capillary wedge pressure (15 +/- 4 vs. 8 +/- 3 mm Hg, p = 0.0001), pulmonary artery pressure (24 +/- 5 vs. 16 +/- 3 mm Hg, p = 0.0001) and right atrial pressure (10 +/- 3 vs. 6 +/- 3 mm Hg, p = 0.008) were all higher in the control group.

CONCLUSIONS

Long-term oral nitrate therapy attenuates the early and late manifestations of ventricular remodeling after myocardial damage in the dog. Hemodynamic observations suggest the possibility that drug-induced preload or afterload reduction does not completely explain this effect.

Ventricular remodeling after myocardial infarction. Experimental and clinical studies

Changes of ischemic myocardium following coronary occlusion, including active and passive functions, and adaptive changes of non-ischemic surviving myocardium have been summarized under the term "left ventricular remodeling" post myocardial infarction. An increase in left ventricular volume may be a consequence, and associated with an adverse prognosis. Although left ventricular dilatation may increase stroke volume and, thus, be compensatory at first, in about one-fifth of patients it ultimately results in progressive dysfunction and heart failure. Major determinants of this process are time, infarct size, infarct location, global left ventricular function assessed 4 days after infarction by radionuclide ejection fraction and right heart catheter (stroke volume), and morphology of the infarct-associated coronary artery. The surviving myocardium hypertrophies and may also dilate structurally. Depression of left ventricular ejection fraction chronically after the infarct is due to deterioration of wall motion of chamber segments initially classified normal by radionuclide analysis. Biochemical changes may also occur, including reduction of phosphocreatine, prolongation of time to peak Cai2+, and changes in myosin isoforms. Systemic or local humoral factors may be involved in these changes, however, clear evidence is still lacking. Perfusion of surviving myocardium may be altered under various conditions due to morphologic and functional changes of coronary vasculature. Successful prevention of heart failure and death by angiotensin converting enzyme inhibitors in asymptomatic patients with left ventricular dysfunction post-myocardial infarction has supported the pathophysiologic concepts of remodeling.

Effects of angiotensin-converting enzyme inhibitors on tissue renin-angiotensin systems

The renin-angiotensin system (RAS) plays a major role in the control of blood pressure and cardiovascular homeostasis and is involved in the pathogenesis of a number of cardiovascular disorders. The efficacy of angiotensin-converting enzyme (ACE) inhibitors in the treatment of hypertension and congestive heart failure has led to the widespread clinical use of ACE inhibitors in primary or secondary prevention of heart disease. The demonstration of the expression of the components of the RAS in several extrarenal tissues, as well as local generation of angiotensin II, has confirmed the existence of a tissue RAS that may serve organ-specific functions and act independently from the plasma RAS. The concept of paracrine/autocrine functions of the local RAS has changed our understanding of the functions of the RAS and suggests that tissue ACE inhibition may be of greater importance than inhibition of circulating ACE in the treatment of congestive heart failure and other cardiovascular disorders. Whereas the circulating endocrine RAS appears to be responsible for mediation of acute effects, the tissue RAS seems to be involved in more chronic situations, such as secondary structural changes of the cardiovascular system, and therefore could contribute to the pathogenesis of hypertension as well as other cardiovascular disorders, such as cardiac hypertrophy, coronary artery disease, and atherosclerosis. Several experimental and clinical findings suggest that reversal of cardiovascular structural changes secondary to cardiovascular disease and enhancement of renal sodium excretion by ACE inhibitors are important long-term antihypertensive actions possibly mediated by inhibition of the tissue RAS.

Cardiac myocyte necrosis induced by angiotensin II

Although the role of angiotensin II (Ang II) in the pathogenesis and progression of the failing heart is uncertain, previous reports have suggested that myocyte injury may be a component in this process. In this study, we investigated this possibility in more detail. Cardiotoxic effects of nonacutely hypertensive doses of Ang II were examined in 90 rats, including those receiving an angiotensin infusion (200 ng/min i.p.) and those with renovascular hypertension, where endogenous stimulation of Ang II occurred. Myocyte injury and wound healing resulting from these treatments were evaluated by 1) immunofluorescence after in vivo monoclonal antibody labeling of myosin to detect abnormal sarcolemmal permeability, 2) [3H]thymidine incorporation into DNA, to detect fibroblast proliferation, and 3) light microscopic evidence of myocytolysis and subsequent scar formation. We found that exogenous Ang II produced multifocal antimyosin labeling of cardiac myocytes and myocytolysis, which were maximal on days 1-2 of the infusion. Subsequently, DNA synthesis rates were increased, with fibroblast proliferation reaching peak levels on day 2 (Ang II-treated rats, 90.0 +/- 18.6 cpm/micrograms DNA; control rats, 11.4 +/- 2.3 cpm/micrograms DNA; p less than 0.05); microscopic scarring was found on day 14 and represented 0.12 +/- 0.02% of the myocardium. Concurrent treatment with both propranolol (30 mg/kg/day s.c.) and phenoxybenzamine (5 mg/kg/day i.m.) did not attenuate Ang II-induced antimyosin labeling. Increased endogenous Ang II, resulting from renal ischemia after abdominal aortic constriction, produced both antimyosin labeling and increased rates of DNA synthesis like that observed with Ang II infusion. Both myocyte injury and fibroplasia were prevented with captopril (65 mg/day p.o.), but this protective effect was not seen with reserpine pretreatment. Infrarenal aortic banding without renal ischemia, on the other hand, produced hypertension without necrosis. We conclude that pathophysiological levels of endogenous as well as low-dose exogenous Ang II were associated with altered sarcolemmal permeability and myocytolysis with subsequent fibroblast proliferation and scar formation. Myocyte injury was unrelated to the hypertensive or enhanced adrenergic effects of Ang II or to hypertension per se. Captopril was effective in preventing myocyte injury in renovascular hypertension. The mechanism(s) responsible for Ang II-induced necrosis will require further study.

Enalapril prevents cardiac fibrosis and arrhythmias in hypertensive rats

To evaluate the effects of hypertension on cardiac hypertrophy, on myocardial structure, and on ventricular arrhythmias, 27 3-month-old spontaneously hypertensive rats were treated with enalapril (10 mg/kg) daily for 11 months and compared with 26 untreated control rats. Systolic arterial pressure was significantly decreased in treated rats, and at the end of the experiment, it was 199 +/- 3 mm Hg (treated) versus 237 +/- 3 mm Hg (controls) (p less than 0.001). At this time, spontaneous arrhythmias and induced arrhythmias either by programmed electrical stimulation (train of stimuli +1 or 2 extrastimuli) or by trains of eight stimuli at decreasing coupling intervals were observed in isolated heart preparations. Comparing enalapril-treated and control rats, spontaneous arrhythmias (9 of 27 versus 20 of 26, respectively; p less than 0.01), programmed stimulation-induced arrhythmias (3 of 26 versus 12 of 23, respectively; p less than 0.01), and trains of stimuli-induced arrhythmias (4 of 26 versus 14 of 19, respectively, p less than 0.001) were less frequent in the enalapril group. Left ventricular weight was decreased in treated rats by 18% (p less than 0.001). Enalapril administration diminished the fraction of myocardium occupied by foci of replacement fibrosis normally occurring in control rats by 59% (p less than 0.001). Finally, a significant correlation was found between left ventricular weight, the extent of myocardial fibrosis, and the occurrence of ventricular fibrillation. It was concluded that chronic treatment with enalapril, which resulted in attenuation of systemic arterial pressure by limiting cardiac hypertrophy and myocardial fibrosis, decreases the propensity of the heart of hypertensive rats to arrhythmogenesis.

Cardioreparative effects of lisinopril in rats with genetic hypertension and left ventricular hypertrophy

BACKGROUND

In genetic and acquired hypertension, a structural remodeling of the nonmyocyte compartment of the myocardium, including the accumulation of fibrillar collagen within the interstitium and adventitia of intramyocardial coronary arteries and a medial thickening of these vessels, represents a determinant of pathological hypertrophy that leads to ventricular dysfunction.

METHODS AND RESULTS

To evaluate the benefit of angiotensin converting enzyme inhibition in reversing this interstitial and vascular remodeling in the rat with genetic spontaneous hypertension (SHR) and established left ventricular hypertrophy (LVH), we treated 14-week-old male SHR with oral lisinopril (average dose, 15 mg/kg/day) for 12 weeks. Myocardial stiffness and coronary vascular reserve to adenosine (800 micrograms/min) were examined in the isolated heart; myocardial collagen and intramural coronary artery architecture were analyzed morphometrically. In lisinopril-treated SHR compared with 14-week-old baseline or 26-week-old untreated SHR and age- and sex-matched Wistar-Kyoto (WKY) controls, we found 1) a regression in LVH and normalization of blood pressure, 2) a complete regression of interstitial fibrosis, represented by a decrease of interstitial collagen volume fraction from 7.0 +/- 1.3% to 3.2 +/- 0.3% (p less than 0.025; WKY, 2.8 +/- 0.5%), 3) normalization of myocardial stiffness constant from 19.5 +/- 0.9 to 13.7 +/- 1.3 (p less than 0.025; WKY, 13.8 +/- 2.2), 4) a reversal of intramural coronary artery remodeling, including a decrease in the ratio of perivascular fibrosis to vessel lumen size from 1.4 +/- 0.2 to 0.4 +/- 0.1 (p less than 0.025; WKY, 0.6 +/- 0.1) and medial thickening from 12.3 +/- 0.6 to 7.4 +/- 0.5 microns (p less than 0.005; WKY, 7.4 +/- 0.4 microns), and 4) a restoration of coronary vasodilator response to adenosine from 12.3 +/- 0.9 to 26.0 +/- 1.4 ml/min/g (p less than 0.005; WKY, 21.8 +/- 2.2 ml/min/g). Thus, in SHR with LVH and adverse structural remodeling of the cardiac interstitium, lisinopril reversed fibrous tissue accumulation and medial thickening of intramyocardial coronary arteries and restored myocardial stiffness and coronary vascular reserve to normal.

CONCLUSIONS

These cardioreparative properties of angiotensin converting enzyme inhibition may be valuable in reversing left ventricular dysfunction in hypertensive heart disease.

Effects of quinapril, a new angiotensin converting enzyme inhibitor, on left ventricular failure and survival in the cardiomyopathic hamster. Hemodynamic, morphological, and biochemical correlates

The effect of chronic therapy with quinapril on the temporal progression of left ventricular failure and survival was assessed in the CHF 146 cardiomyopathic (CM) hamster, which is an idiopathic model of congestive heart failure. Age-matched Golden Syrian (GS) hamsters served as normal controls. Quinapril was administered in the drinking water at average daily doses of 10.2, 112.4, and 222.4 mg/kg/day. In untreated CM hamsters, in vitro left ventricular performance progressively deteriorated with increasing age beginning at roughly 180 days. This decline in left ventricular performance was accompanied by a decrease in coronary flow and an increase in left ventricular volume. Administration of quinapril from 180 to 300 days of age prevented the decline of in vitro left ventricular contractile performance and coronary flow and also reduced the age-dependent increases in left ventricular volume. The cardioprotective effects of quinapril were observed at doses of 112.4 and 222.4 mg/kg/day but not at 10.2 mg/kg/day. Lung angiotensin converting enzyme activity was significantly inhibited by quinapril in GS and CM hamsters at 240 and 300 days of age at all dose levels. In contrast, significant inhibition of ventricular angiotensin converting enzyme activity was observed consistently at doses of 112.4 and 222.4 mg/kg/day quinapril but not at 10.2 mg/kg/day. In the survival protocol, CM and GS hamsters were treated with vehicle or quinapril (100 mg/kg/day) from 180 to 522 days of age. During the initial 210 days of treatment (from 180 to 390 days of age) 78.3% of the vehicle-treated CM hamsters died compared with 27.7% of quinapril-treated CM hamsters. Quinapril increased the median survival time of CM hamsters by 32.9% (112 days). It is concluded that chronic quinapril therapy exerts a significant cardioprotective effect and also increases survival.

Remodeling of the rat right and left ventricles in experimental hypertension

Pathological left ventricular hypertrophy in renovascular hypertension is associated with the accumulation of fibrillar collagen within the extracellular space and around intramyocardial coronary arteries. Even though the angiotensin converting enzyme inhibitor captopril was previously found to attenuate this interstitial and perivascular fibrosis, the relative importance of arterial and ventricular systolic pressures versus circulating angiotensin II (AII) and aldosterone (AL) in promoting hypertrophy and collagen accumulation in renovascular hypertension is uncertain. By drawing on the in-parallel arrangement of the right and left ventricles, with respect to their coronary circulation, and the in-series mechanical alignment of the ventricles, with a pressure-overloaded left and a normotensive right ventricle, this study sought to address this uncertainty. Three models of experimental hypertension, each having a different circulating AII and AL profile, were examined and compared with their controls: renovascular hypertension, where both AII and AL are increased; infrarenal aorta banding, where AII and AL are normal; and a chronic infusion of AL, where AII is suppressed or normal and AL is increased. In renovascular hypertension, as well as with AL, we found a significant rise in the interstitial collagen volume fraction and perivascular collagen area of the pressure-overloaded, hypertrophied left ventricle as well as the normotensive, nonhypertrophied right ventricle. This remodeling was not seen in either ventricle with infrarenal aorta banding despite comparable systemic hypertension and left ventricular hypertrophy. Thus, in experimental arterial hypertension in the rat, myocyte and nonmyocyte compartments of the myocardium are under separate controls: myocyte hypertrophy is most closely related to ventricular loading while circulating AII and AL, acting alone or in concert with other humoral factors, regulate the accumulation of collagen within the right and left ventricles.