Captopril reduces purine loss and reperfusion arrhythmias in the rat heart after coronary artery occlusion

Role of Oxidative Stress in the Genesis of Ventricular Arrhythmias

Ventricular arrhythmias, mainly lethal arrhythmias, such as ventricular tachycardia and fibrillation, may lead to sudden cardiac death. These are triggered as a result of cardiac injury due to chronic ischemia, acute myocardial infarction and various stressful conditions associated with increased levels of circulating catecholamines and angiotensin II. Several mechanisms have been proposed to underlie electrical instability of the heart promoting ventricular arrhythmias; however, oxidative stress which adversely affects ion homeostasis due to changes in the ion channel structure and function, seems to play a critical role in eliciting different types of ventricular arrhythmias. Prevention or mitigation of the severity of ventricular arrhythmias due to antioxidants has been indicated as the fundamental contribution in the field of preventive cardiology; however, novel interventions have to be developed for greater effectiveness and specificity in attenuating the adverse effects of oxidative stress. In this review, we have attempted to discuss proarrhythmic effects of oxidative stress differing in time and concentration dependence and highlight a molecular and cellular concept how it alters cardiac cell automaticity and conduction velocity sensitizing the probability of ventricular arrhythmias with resultant sudden cardiac death due to ischemic heart disease and other stressful situations. It is concluded that pharmacological approaches targeting multiple mechanisms besides oxidative stress might be more effective in the treatment of ventricular arrhythmias than current antiarrhythmic therapy.

A Novel Category of Anti-Hypertensive Drugs for Treating Salt-Sensitive Hypertension on the Basis of a New Development Concept

Terrestrial animals must conserve water and NaCl to survive dry environments. The kidney reabsorbs 95% of the sodium filtered from the glomeruli before sodium reaches the distal connecting tubules. Excess sodium intake requires the renal kallikrein-kinin system for additional excretion. Renal kallikrein is secreted from the distal connecting tubule cells of the kidney, and its substrates, low molecular kininogen, from the principal cells of the cortical collecting ducts (CD). Formed kinins inhibit reabsorption of NaCl through bradykinin (BK)-B₂ receptors, localized along the CD. Degradation pathway of BK by kinin-destroying enzymes in urine differs completely from that in plasma, so that ACE inhibitors are ineffective. Urinary BK is destroyed mainly by a carboxypeptidase-Y-like exopeptidase (CPY) and partly by a neutral endopeptidase (NEP). Inhibitors of CPY and NEP, ebelactone B and poststatin, respectively, were found. Renal kallikrein secretion is accelerated by potassium and ATP-sensitive potassium (KATP) channel blockers, such as PNU-37883A. Ebelactone B prevents DOCA-salt hypertension in rats. Only high salt intake causes hypertension in animals deficient in BK-B2 receptors, tissue kallikrein, or kininogen. Hypertensive patients, and spontaneously hypertensive rats, excrete less kallikrein than normal subjects, irrespective of races, and become salt-sensitive. Ebelactone B, poststatin, and KATP channel blockers could become novel antihypertensive drugs by increase in urinary kinin levels. Roles of kinin in cardiovascular diseases were discussed.

Erythropoietin improves left ventricular function and coronary flow in an experimental model of ischemia-reperfusion injury

BACKGROUND

Recent studies show that erythropoietin (EPO) plays a protective role in brain ischemia. In this condition, administration of EPO protects neurons from ischemic damage. Recently, it has been shown that in patients with chronic heart failure (CHF), EPO treatment improved cardiac function. In the present study we assessed the role of EPO and EPO-receptor (EPO-R) in the heart.

METHODS AND RESULTS

We studied the presence and functionality of the EPO-R in isolated rat hearts in the Langendorff set-up. Hearts were perfused for 20 min with 10 U/ml EPO or vehicle. Immunohistochemistry revealed the presence of the EPO-R on endothelial cells, fibroblasts and to a lesser extent cardiomyocytes. Furthermore, perfusion with EPO resulted in a 50% increase in the phosphorylated MAP kinases p42/p44. To evaluate the protective role of EPO in cardiac ischemia, we performed low-flow (0.6 ml/min) ischemia/reperfusion experiments in isolated rat hearts. Administration of EPO (10 U/ml) reduced the cellular damage by 56% (P<0.05) during reperfusion, diminished apoptosis by 15% (P<0.05) and resulted in a significantly improved recovery of left ventricular pressure (P=0.02) and coronary flow (P=0.01).

CONCLUSION

The present data suggest that a functional EPO-R is present in rat adult cardiac tissue and that exogenous EPO administration improves cardiac function after ischemia/reperfusion injury.

Protection of the cardiovascular system by imidapril, a versatile angiotensin-converting enzyme inhibitor

Imidapril hydrochloride (imidapril) is a long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor, which has been used clinically in the treatment of hypertension, chronic congestive heart failure (CHF), acute myocardial infarction (AMI), and diabetic nephropathy. It has the unique advantage over other ACE inhibitors in causing a lower incidence of dry cough. After oral administration, imidapril is rapidly converted in the liver to its active metabolite imidaprilat. The plasma levels of imidaprilat gradually increase in proportion to the dose, and decline slowly. The time to reach the maximum plasma concentration (T(max)) is 2.0 h for imidapril and 9.3 h for imidaprilat. The elimination half-lives (t(1/2)) of imidapril and imidaprilat is 1.7 and 14.8 h, respectively. Imidapril and its metabolites are excreted chiefly in the urine. As an ACE inhibitor, imidaprilat is as potent as enalaprilat, an active metabolite of enalapril, and about twice as potent as captopril. In patients with hypertension, blood pressure was still decreased at 24 h after imidapril administration. The antihypertensive effect of imidapril was dose-dependent. The maximal reduction of blood pressure and plasma ACE was achieved with imidapril, 10 mg once daily, and the additional effect was not prominent with higher doses. When administered to patients with AMI, imidapril improved left ventricular ejection fraction and reduced plasma brain natriuretic peptide (BNP) levels. In patients with mild-to-moderate CHF [New York Heart Association (NYHA) functional class II-III], imidapril increased exercise time and physical working capacity and decreased plasma atrial natriuretic peptide (ANP) and BNP levels in a dose-related manner. In patients with diabetic nephropathy, imidapril decreased urinary albumin excretion. Interestingly, imidapril improved asymptomatic dysphagia in patients with a history of stroke. In the same patients it increased serum substance P levels, while the angiotensin II receptor antagonist losartan was ineffective. These studies indicate that imidapril is a versatile ACE inhibitor. In addition to its effectiveness in the treatment of hypertension, CHF, and AMI, imidapril has beneficial effects in the treatment of diabetic nephropathy and asymptomatic dysphagia. Good tissue penetration and inhibition of tissue ACE by imidapril contributes to its effectiveness in preventing cardiovascular complications of hypertension. The major advantages of imidapril are its activity in the treatment of various cardiovascular diseases and lower incidence of cough compared with some of the older ACE inhibitors.

Increased kallikrein expression protects against cardiac ischemia

Multiple indirect lines of evidence point at a cardioprotective role for enhanced bradykinin formation. In particular, the inhibition of angiotensin-converting enzyme, also known as kininase II, can protect against cardiac ischemia, putatively via accumulation of bradykinin. To address whether an increase in kinin formation is sufficient to protect against cardiac ischemia, we studied transgenic rats harboring the human tissue kallikrein gene TGR(hKLK1) under the control of the metallothionein promoter, which drives expression of the transgene in various organs including the heart. We subjected the isolated hearts from transgenic rats and their transgene negative littermates to ex vivo regional cardiac ischemia and reperfusion. During the experiment, the hearts were treated with either vehicle or the specific bradykinin type 2 receptor antagonist HOE 140 (10-9 M). In the transgenic rats, overflow of nucleotide breakdown products upon reperfusion was significantly less (455 +-54 nmol/min/g in transgene negative rats vs. 270+-57 nmol/min/g in the transgenic rats, P.

Force-length relationship in dogs as a measure of protective effect of imidapril on regional myocardial ischemia and reperfusion injury

Our laboratory previously reported that the end-systolic force-length relationship of the left ventricle provides a better method of evaluating myocardial contractile properties than the left ventricular end-systolic pressure-volume relationship, because it avoids deficiencies of the latter parameter such as dependence of its slope (E(max)) on the volume intercept (V(0)). The slope (E(c)) of the left ventricular end-systolic force-length relationship represents the contractility of functioning myocardium, while its length intercept (L(0)) reflects the length of non-functioning myocardium. However, the effect of regional myocardial ischemia on these parameters, as evaluated by the force-length relationship, remains unknown. To clarify the effects of regional ischemia and angiotensin-converting enzyme inhibition on the myocardium during ischemia-reperfusion, the changes in E(c) and L(0) were determined in anesthetized open-chest dogs. (1) Control group (n=26): Before and after 15 min of complete coronary artery occlusion, as well as after 15 min of reperfusion, left ventricular pressure and volume were simultaneously recorded during inferior vena cava occlusion. The left ventricular force-length relationship was obtained from the pressure and volume of three cylindrical segments of the ventricle, and E(c) and L(0) were calculated. (2) Imidapril group (n=14): Imidaprilat (1 microg/kg/min) was continuously infused from 30 min before ischemia to the end of the experiment, and the same procedures were followed as in the control group. Fourteen out of the 26 dogs (54%) in the control group died of reperfusion-induced ventricular arrhythmias, while only two of the 14 dogs (14%) in the imidapril group did so (P<0.05). In the control group, E(c) was increased during ischemia and remained at the same level after reperfusion. However, E(c) was not altered in the imidapril group. Although L(0) was increased during ischemia and decreased after reperfusion in both groups, the percent increase of L(0) in the imidapril group was significantly smaller than in the control group (8% vs. 32%, P<0.05). With the improvement of these indices, the bradykinin concentration of coronary venous blood increased in the imidapril group (P<0.01). These findings suggest that regional myocardial ischemia increased the average contractility of overall functioning myocardium despite the increased non-functioning myocardium. Moreover, imidapril has a cardioprotective effect against ischemia-reperfusion injury by decreasing infarct size, and through the antiarrhythmic effect and the reversal of increased overall contractility.

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.

Left ventricular dilatation after myocardial infarction: ACE inhibitors, beta-blockers, or both?

Left ventricular (LV) dilatation after myocardial infarction (MI) is a major predictor of prognosis and identifies which patients will develop heart failure. Left ventricular dilatation or remodeling starts immediately after MI and progresses in the chronic phase of heart failure. Factors influencing remodeling, such as infarct size and neurohumoral activation, including the sympathetic and renin-angiotensin system, are discussed. Remodeling can be affected by reduction of infarct size and inhibition of neurohumoral activation. The effect of thrombolysis, beta-blockade, and angiotensin-converting enzyme (ACE) inhibition in the acute phase after MI and in the chronic phase of heart failure on remodeling are discussed. On the basis of beneficial effects of ACE inhibition and beta-blockade in acute MI and in chronic heart failure, a treatment strategy is proposed in which both ACE inhibition and beta-blockade are started early after MI. Depending on infarct size and ventricular function, continued treatment in the chronic phase of heart failure must be considered.

Electrocardiographic Changes and Mortality Due to Myocardial Infarction in Rats With or Without Imidapril Treatment

BACKGROUND: Various angiotensin-converting enzyme inhibitors are known to improve heart function and prolong survival in patients and animals after myocardial infarction. Because myocardial infarction is known to induce arrhythmias, this study tested the hypothesis that early treatment with the angiotensin converting enzyme inhibitor imidapril reduces mortality during acute myocardial infarction because of protective effects against arrhythmogenesis. METHODS AND RESULTS: Rats were randomly divided into four groups: sham control, myocardial infarction, sham plus imidapril, and myocardial infarction plus imidapril. Myocardial infarction was produced by ligation of the left anterior descending coronary artery. Treated rats received imidapril (1 mg/kg/day) through a gastric tube beginning 1 hour after coronary occlusion; control rats received tap water. Electrocardiogram (ECGs) were recorded 1, 3, 7, and 21 days postocclusion. Infarct size and scar weight were determined at 21 days in the myocardial infarction groups with and without imidapril treatment. ECGs of untreated rats showed ST-segment changes, abnormal Q waves, premature ventricular complexes, and QT(c) prolongation 1-21 days after coronary occlusion. Total mortality in 21 days averaged 35% in untreated rats; mortality within 48 hours was 30%. On the other hand, imidapril-treated rats showed fewer ST-segment changes, fewer abnormal Q waves, and a decreased incidence of premature ventricular complexes after coronary occlusion; the ST-segment and QT(c) interval returned to basal values within 1 week after occlusion. Imidapril treatment did not affect the ECG pattern in sham-treated control animals. Total mortality in the imidapril-treated group in 21 days after infarction was 22.5%; mortality within 48 hours was 20% (P <.05 compared with the untreated infarction group). Infarct size and scar weight caused by coronary occlusion did not differ in the untreated and imidapril-treated groups. CONCLUSIONS: Early treatment with imidapril markedly decreases mortality in rats after acute myocardial infarction. The lower mortality is not associated with a decrease in infarct size but is consistent with a protective effect of the drug against arrhythmogenesis.

Protective effect of the angiotensin-converting enzyme inhibitor captopril on postischemic myocardial damage in perfused rat heart

This study was undertaken to examine whether a sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitor, captopril, improves postischemic cardiac function and myocardial metabolism in the perfused working rat heart, and to elucidate the mechanism by which captopril protects the myocardium from postischemic damage. Isolated rat hearts were perfused by the working heart technique for 15 min. Ischemia was then induced for 30 min by lowering the afterload pressure and coronary flow to zero. After ischemia, hearts were reperfused for 30 min by returning afterload pressure to 60 mmHg. Captopril, a non-sulfhydryl-containing ACE inhibitor, enalapril, or a type 1 angiotensin II receptor antagonist, DuP 753, was added to the perfusate 5 min before ischemia, and the treatment was continued during the first 10-min period of reperfusion. In all groups there was no significant difference in pressure-rate product, coronary flow, tissue levels of ATP, total adenine nucleotides (TANs), energy charge potential (ECP), or creatine phosphate (CrP) before and during ischemia. During reperfusion following ischemia, captopril significantly improved the recovery of pressure-rate product, coronary flow, and tissue levels of ATP, TAN, ECP, and CrP, but neither enalapril nor DuP 753 had an effect. In conclusion, captopril improved postischemic cardiac function and myocardial metabolism in the perfused rate heart and its effect was independent of the blunting of angiotensin II formation.

Early pharmacologic intervention may prevent the deterioration in endothelial function after experimental myocardial infarction in rats: effects of ibopamine and captopril

BACKGROUND

Endothelial function is progressively disturbed after myocardial infarction (MI), which may be related to both neurohumoral activation and hemodynamic alterations. Consequently, it may be suggested that drugs that favorably affect these factors may also have a positive effect on endothelial function.

METHODS AND RESULTS

Rats underwent coronary ligation (n = 24) or remained unoperated (n = 21), and were randomized to captopril (25 mg/kg/d) or ibopamine (10 mg/kg/d) or remained untreated. Treatment was started following MI and lasted 8 weeks, after which rats were sacrificed for in vitro studies. Left ventricular end-systolic pressure was higher in rats treated with captopril (83 +/- 6 mmHg) and ibopamine (80 +/- 3 mmHg), as compared with untreated MI rats (48 +/- 6 mmHg, P < .01 for both). Increased plasma norepinephrine levels in MI rats were reduced by captopril and ibopamine (both P < .05). Infarct size was smaller in rats treated with captopril (26.7 +/- 3.6%, P < .05) and ibopamine (31.4 +/- 4.3%, P = NS), as compared with untreated rats (41.7 +/- 2.4%). Maximal endothelium-dependent relaxation (Emax; % precontraction) and the concentration of methacholine causing 50% Emax, expressed as negative log(pIC50) were significantly reduced in aortic rings from MI control subjects (pIC50 = 6.15 +/- 0.06 mol/L, Emax = 32.0 +/- 4.2%), as compared with normal control subjects (pIC50 = 6.57 +/- 0.07 mol/L, P < .001; Emax = 50.0 +/- 4.9%, P = .022). Captopril (pIC50 = 6.30 +/- 0.08 mol/L, Emax = 45.1 +/- 7.0%) and ibopamine (pIC50 = 6.60 +/- 0.08 mol/L, Emax = 43.8 +/- 5.2%) improved these parameters in MI rats.

CONCLUSION

The results demonstrate preservation of endothelial function by early pharmacologic intervention after experimental MI in rats in the setting of concomitant reduction in infarct size.

Renin-angiotensin system components in the interstitial fluid of the isolated perfused rat heart. Local production of angiotensin I

We used a modification of the isolated perfused rat heart, in which coronary effluent and interstitial transudate were separately collected, to investigate the uptake and clearance of exogenous renin, angiotensinogen, and angiotensin I (Ang I) as well as the cardiac production of Ang I. The levels of these compounds in interstitial transudate were considered to be representative of the levels in the cardiac interstitial fluid. During perfusion with renin or angiotensinogen, the steady-state levels (mean +/- SD) in interstitial transudate were 64 +/- 34% (P < .05 for difference from the arterial level, n = 8) and 108 +/- 42% (n = 6) of the arterial level, respectively; the levels in coronary effluent were not significantly different from those in interstitial transudate. Ang I was not detectable in interstitial transudate during perfusion with Tyrode's buffer or angiotensinogen. It was very low in interstitial transudate during perfusion with renin and rose to much higher levels during combined renin and angiotensinogen perfusion. The total production rate of Ang I present in interstitial fluid could be largely explained by the renin-angiotensinogen reaction in the fluid phase of the interstitial compartment. In contrast, the total production rate of Ang I present in coronary effluent and the net ejection rate of Ang I via coronary effluent were, respectively, 4.6 +/- 2.2 and 2.8 +/- 1.3 (P < .01 and P < .05 for difference from 1.0, n = 6) times higher than could be explained by Ang I formation in the fluid phase of the intravascular compartment. Ang I from the interstitial fluid contributed little to the Ang I in the intravascular fluid and vice versa. These data reveal two tissue sites of Ang I production, ie, the interstitial fluid and a site closer to the blood compartment, possibly vascular surface-bound renin. There was no evidence that the release of locally produced Ang I into coronary effluent and interstitial transudate occurred independently of blood-derived renin or angiotensinogen.

Which patient benefits from early angiotensin-converting enzyme inhibition after myocardial infarction? Results of one-year serial echocardiographic follow-up from the Captopril and Thrombolysis Study (CATS)

OBJECTIVES

In this study we sought to investigate the effect of intervention with captopril within 6 h of the onset of myocardial infarction on left ventricular volume and clinical symptoms of heart failure in relation to infarct size during a 1-year follow-up period.

BACKGROUND

Remodeling of the heart starts in the early phase of myocardial infarction and is associated with an adverse prognosis. Angiotensin-converting enzyme inhibition started in the subacute or late phase after myocardial infarction has been shown to improve prognosis.

METHODS

In the Captopril and Thrombolysis Study, 298 patients with a first anterior myocardial infarction treated with intravenous streptokinase were randomized to receive either oral captopril (25 mg three times a day) or placebo. The left ventricular volume index was assessed by two-dimensional echocardiography within 24 h, on days 3, 10 and 90 and after 1 year.

RESULTS

A small but significant increase in left ventricular volume indexes was observed after 12 months. Using a random coefficient model, no significant treatment effect on left ventricular volumes could be detected. In contrast, when survival models were used, the occurrence of left ventricular dilation was significatnly lower in captopril-treated patients (p = 0.018). In addition, the incidence of heart failure was lower in the captopril group (p < 0.03). This effect appeared early and was most obvious in patients with a medium-sized infarct (p = 0.04) and was not present in large infarcts.

CONCLUSIONS

Very early treatment with captopril after myocardial infarction significantly reduces the occurrence of early dilation and the progression to heart failure. These data underscore the importance of early treatment. Furthermore, patients with intermediate infarct size benefit the most from this treatment strategy.

Attenuation of reperfusion arrhythmias by selective inhibition of angiotensin-converting enzyme/kininase II in the ischemic zone: mediated by endogenous bradykinin?

We studied the effects of angiotensin-converting enzyme (ACE)/kininase II inhibition selectively in the ischemic zone on reperfusion arrhythmias, and the role of bradykinin versus angiotensin II (produced locally in this zone) in modulating the severity of such arrhythmias. Isolated rat hearts (n = 12 per group) were subjected to independent perfusion of left and right coronary beds. The left coronary bed received the ACE/kininase II inhibitor ramiprilat, alone or in combination with either HOE140 (bradykinin B2 receptor antagonist) or angiotensin II, before induction of regional ischemia (10 min) by discontinuation of flow to the bed. Ramiprilat (1, 10, or 100 nM) did not significantly alter the incidence of reperfusion-induced ventricular tachycardia (VT) or fibrillation (VF), but reduced the incidence of sustained VF from 83% in controls to 75, 50, and 25% (p < 0.05). The protective effects of 100 nM ramiprilat were abolished by coinfusion of HOE140 (10 or 100 nM) but not affected by coinfusion of angiotensin II (1 nM). HOE140 (10 nM), when infused alone into the left coronary bed before 7-min ischemia, increased the incidence of sustained VF from 42 to 100% (p < 0.05). Although HOE140 caused vasoconstriction in the left coronary bed when given alone or in combination with ramiprilat, its proarrhythmic effects were not due to a reduction of flow to the bed. We conclude that selective inhibition of ACE/kininase II in the ischemic zone moderately attenuates reperfusion arrhythmias and that enhanced bradykinin availability rather than reduced angiotensin II in synthesis contributes to such an effect.

Effect of captopril on membrane currents of ventricular myocytes

Using whole-cell patch-clamp technique, the present study examined the effects of captopril on membrane currents of ventricular myocytes. The results were as follow: when the concentration of captopril was 6 x 10(-4)mol, the fast inward sodium current and slow inward calcium current were all decreased significantly (P < 0.05). Besides, when the concentration exceeds 10(-3)mol, the delayed rectifier potassium current was increased (P < 0.05) as well. But if the experimental concentration was under 6 x 10(-4)mol, these three kinds of currents was not affected. These findings suggested that captopril has no direct antiarrhythmic effect at the average therapeutic serum level.

Expanding the paradigm of the renin-angiotensin system and angiotensin-converting enzyme inhibitors

The renin-angiotensin system acts systemically and locally to influence vascular tone, blood volume, myocardial contractility, thromboresistance, and tissue responses to injury. ACE inhibitors have assumed a vital role in the treatment of patients with ventricular dysfunction, including those who have sustained one or more myocardial infarctions. The greatest benefits appear over time and not unexpectedly are most pronounced in cases of moderate to severe reduction in left ventricular performance. Emerging evidence suggests that the paradigm for ACE inhibitor use will expand even further, opening new doors for patient care.

Effect of the angiotensin-converting enzyme inhibitor, perindoprilat, and of angiotensin-II on the transient inward current of rabbit ventricular myocytes

Angiotensin-converting enzyme (ACE) inhibitors protect the myocardium from experimental lethal ventricular arrhythmias induced by ischemia or reperfusion. Hypothetically, such arrhythmias may result from the calcium-dependent transient inward current Iti. It is already known that perindoprilat decreased the transient inward current in guinea-pig myocytes [1]. In the same preparation, however, angiotensin-II decreased the transient inward current, an effect opposite to that required to prove that the ACE inhibitor exerted its beneficial effects on Iti by lessening the action of angiotensin-II. We, therefore, selected another species, the rabbit, in which angiotensin-II was known to have a positive inotropic effect. Perindoprilat (1 microM but not 0.01 microM) decreased the transient inward current from -8.93 +/- 0.80 microA/cm2 to -5.33 +/- 0.74 microA/cm2 (p < 0.05). Perindoprilat (1 microM) also protected from the effects of angiotensin-II (0.01 and 0.1 microM), which on its own increased the amplitude of the transient inward current. Based on our results, we conclude that perindoprilat (1 microM) prevents the effect of angiotensin-II in promoting the transient inward current in the rabbit. Hence our data support the hypothesis that the ACE inhibitor, perindoprilat, might in relatively high concentrations have an antiarrhythmic effect, at least in part through inhibition of angiotensin-II-evoked calcium-dependent Iti.

Failure of captopril to attenuate myocardial damage, neutrophil accumulation, and mortality following coronary artery occlusion and reperfusion in rat

Captopril, a sulfhydryl-containing angiotensin-converting enzyme inhibitor, has been suggested as possessing antiischemic and antiinflammatory properties. To test the hypothesis that captopril may prevent neutrophil-induced myocardial injury during acute myocardial infarction (AMI), the authors subjected rats to coronary occlusion for thirty minutes and reperfusion for twenty-four hours (MI) or to sham operation (sham MI). Oral captopril (100 mg/kg) or vehicle was administered thirty minutes before coronary occlusion. The effect of captopril on mean arterial blood pressure was assessed in separate group of animals (n = 8). Infarct size and neutrophil accumulation in myocardium were determined by measuring creatine phosphokinase depletion and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Animals treated with 100 mg/kg of captopril exhibited significant reduction in mean arterial blood pressure compared with vehicle-treated animals (P < 0.01). Compared with vehicle-treated animals, administration of 100 mg/kg of captopril to MI animals attenuated neither twenty-four-hour mortality (56% vs 52%, respectively), nor infarct size (36 +/- 7% vs 34% +/- 7% respectively), nor MPO activity (1.0 +/- 0.17 vs 1.26 +/- 0.19). Thus, in the present experiment captopril did not reduce neutrophil-induced myocardial damage following coronary occlusion and reperfusion. These findings may be partly explained by the negative effect of captopril on arterial blood pressure during AMI.

Cardiac renin and angiotensins. Uptake from plasma versus in situ synthesis

The existence of a cardiac renin-angiotensin system, independent of the circulating renin-angiotensin system, is still controversial. We compared the tissue levels of renin-angiotensin system components in the heart with the levels in blood plasma in healthy pigs and 30 hours after nephrectomy. Angiotensin I (Ang I)-generating activity of cardiac tissue was identified as renin by its inhibition with a specific active site-directed renin inhibitor. We took precautions to prevent the ex vivo generation and breakdown of cardiac angiotensins and made appropriate corrections for any losses of intact Ang I and II during extraction and assay. Tissue levels of renin (n = 11) and Ang I (n = 7) and II (n = 7) in the left and right atria were higher than in the corresponding ventricles (P < .05). Cardiac renin and Ang I levels (expressed per gram wet weight) were similar to the plasma levels, and Ang II in cardiac tissue was higher than in plasma (P < .05). The presence of these renin-angiotensin system components in cardiac tissue therefore cannot be accounted for by trapped plasma or simple diffusion from plasma into the interstitial fluid. Angiotensinogen levels (n = 11) in cardiac tissue were 10% to 25% of the levels in plasma, which is compatible with its diffusion from plasma into the interstitium. Like angiotensin-converting enzyme, renin was enriched in a purified cardiac membrane fraction prepared from left ventricular tissue, as compared with crude homogenate, and 12 +/- 3% (mean +/- SD, n = 6) of renin in crude homogenate was found in the cardiac membrane fraction and could be solubilized with 1% Triton X-100. Tissue levels of renin and Ang I and II in the atria and ventricles were directly correlated with plasma levels (P < .05), and in both tissue and plasma the levels were undetectably low after nephrectomy. We conclude that most if not all renin in cardiac tissue originates from the kidney. Results support the contentions that in the healthy heart, angiotensin production depends on plasma-derived renin and that plasma-derived angiotensinogen in the interstitial fluid is a potential source of cardiac angiotensins. Binding of renin to cardiac membranes may be part of a mechanism by which renin is taken up from plasma.

A patient in whom self-terminating ventricular fibrillation was a manifestation of myocardial reperfusion

Self-terminating ventricular fibrillation was recorded in a 47 year old woman without coronary artery or other structural heart disease. Reperfusion was thought to be responsible for the ventricular fibrillation because the arrhythmia started while the ST segment was returning to the baseline during an episode of silent ischaemia that was probably caused by coronary spasm. This case shows that potentially lethal arrhythmias can arise during reperfusion and that ventricular fibrillation during reperfusion may be self-terminating.

Reduction of exercise-induced ventricular arrhythmias in mild symptomatic heart failure by benazepril

We studied 14 patients who had exercise-induced ventricular arrhythmias after a previous Q-wave myocardial infarction. All had symptomatic mild heart failure in New York Heart Association class II and a maximal oxygen consumption between 16 and 20 ml/kg/min. They were treated with the angiotensin converting enzyme inhibitor benazepril (20 mg) and hydrochlorothiazide (50 mg) for 3 months in a double-blind randomized cross-over study. Benazepril improved the maximal oxygen uptake by 15% and exercise time by 18%. Hydrochlorothiazide slightly increased exercise time (5%) and the respiratory exchange ratio but not oxygen consumption. The arrhythmias were nonsustained and reproducible in two baseline recordings. Compared with baseline, benazepril reduced the mean number (3.5 +/- 2.5) (+/- SD) of episodes of ventricular tachycardia by 66%, and total (47.4 +/- 40.9) and paired (5.2 +/- 4.5) premature ventricular contractions by 61% and 62%, respectively. Hydrochlorothiazide did not reduce the number of arrhythmias. Thus an improved cardiac function induced by benazepril is associated with a reduction in exercise-induced ventricular arrhythmias in patients with symptomatic mild heart failure after infarction.

ACE-inhibitors in coronary artery disease?

Angiotensin converting enzyme (ACE)-inhibitors are established in the treatment of arterial hypertension and heart failure. In recent years ACE-inhibitors have also been used in the treatment of patients with coronary artery disease (CAD), since from experimental data an antiischemic action of these agents is suggested. Antiischemic effects of ACE-inhibitors may be exerted through a reduction of myocardial oxygen demand, by a reduction of angiotensin-mediated coronary vasoconstriction, by an interaction with bradykinin and the prostaglandin system, by a modulation of endothelial control of vascular tone, and by an interaction with the sympathetic nervous system. However, clinical findings on potential beneficial effects of ACE-inhibitors in patients with CAD are inconsistent and controversial. While in hypertensive patients with CAD ACE-inhibitors generally seem to attenuate myocardial ischemia at rest and during exercise, a significant fraction of about 30% of normotensive patients with CAD does not benefit or even deteriorates. Lowering of coronary perfusion pressure and alteration of transmural blood flow distribution may be responsible for this. In patients with left ventricular dysfunction (SOLVD) or congestive heart failure (CONSENSUS, SOLVD) ACE-inhibitors have been proven to prevent progressive deterioration in left ventricular function and to reduce mortality. In patients with asymptomatic left ventricular dysfunction after myocardial infarction (SAVE), long-term administration of captropril was associated with an improvement in survival and reduced morbidity and mortality due to major cardiovascular events. Therefore, from a prognostic viewpoint patients with CAD and left ventricular dysfunction or congestive heart failure should be treated with ACE-inhibitors, although the clinical use of ACE-inhibitors in patients with ongoing angina pectoris may be limited by an aggravation of angina, presumably due to critically lowering coronary perfusion pressure. Finally, ACE-inhibitors failed to prevent restenosis after successful PTCA. In conclusion, from a prognostic viewpoint patients with CAD and congestive heart failure or left ventricular dysfunction should be treated with ACE-inhibitors. In hypertensive patients ACE-inhibitors generally seem to attenuate myocardial ischemia. In normotensive patients with CAD and angina pectoris but without left ventricular dysfunction ACE-inhibitors cannot generally be recommended at present, unless the patients, which may have benefit from ACE-inhibitor treatment can be better defined.

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.

Detection of angiotensin I and II in cultured rat cardiac myocytes and fibroblasts

Angiotensin II (ANG II) is a stimulus for positive chronotropic and inotropic effects, protein synthesis, and hypertrophic growth in cardiac tissue. These short- and long-term effects of ANG II are mediated through specific plasma membrane receptors. Indirect evidence suggests that ANG II synthesized in the myocardium may be important in regulating cardiac function. The cell types in the myocardium that produce components of the renin-angiotensin system have not been determined. In this study, we evaluated whether cultured cardiomyocytes and fibroblasts obtained from ventricles of neonatal rat hearts were capable of synthesizing ANG I and II. Both cardiomyocytes and fibroblasts were found to have immunofluorescent staining for ANG I, ANG II, and angiotensin-converting enzyme (ACE). The amounts of ANG I and II in cell extracts and conditioned media obtained from cardiomyocytes and fibroblasts were quantified by radioimmunoassay. The amounts of ANG I and II detected in cardiomyocyte cultures (1.48 x 10(6) cells/dish) were 32.2 +/- 16.2 (n = 4) and 6.2 +/- 2.9 (n = 4) ng/10(6) cells, respectively. The amounts of ANG I and II detected in the media conditioned by a 48-h exposure to cardiomyocytes were 5.2 +/- 1.2 (n = 3) and 2.1 +/- 1.2 (n = 3) ng/10(6) cells, respectively. The amounts of ANG I and II detected in fibroblast cultures (5.38 x 10(6) cells/dish) were 34.8 +/- 4.9 (n = 4) and 8.0 +/- 3.5 (n = 4) ng/10(6) cells, respectively. The amounts of ANG I and II obtained from media conditioned by a 48-h exposure to fibroblasts were 4.7 +/- 0.6 (n = 4) and 3.3 +/- 2.1 (n = 4) ng/10(6) cells, respectively. The identity of the radioimmunoassayable materials as ANG I and II peptides was confirmed in cardiomyocytes using an in vitro bioassay based on displacement of 125I-ANG II from receptor binding sites in cardiac membranes prepared from neonatal pig heart. Identification of ANG I and II and ACE in vitro in cultures of cardiac myocytes and fibroblasts supports the hypothesis that there is an intracardiac renin-angiotensin system that produces these peptides.

The myocardial renin-angiotensin system: existence, importance, and clinical implications

Major components of the renin-angiotensin system have been localized to cardiac tissue. Cardiac-derived angiotensin II may benefit myocardial contractility but may promote detrimental myocardial hypertrophy, coronary vasoconstriction, and arrhythmias. The benefits of ACE inhibition probably extend beyond the classic circulating RAS to include the heart directly.

Early intervention with angiotensin-converting enzyme inhibitors during thrombolytic therapy in acute myocardial infarction: rationale and design of captopril and thrombolysis study. CATS investigators group

The adjunctive use of angiotensin-converting enzyme (ACE) inhibitors with thrombolytic therapy early during acute myocardial infarction offers theoretic advantages. In the acute phase, captopril may scavenge free radicals, blunt the catecholamine response, elicit coronary vasodilation, and increase prostacyclin and bradykinin levels. In the chronic phase, ventricular remodeling may be attenuated. At present, a large number of controlled clinical trials mainly focusing on the effects of ACE inhibition in the chronic phase are underway. Only a few studies concentrate on the effect of acute intervention with ACE inhibitors in ischemia-reperfusion, i.e., thrombolysis in myocardial infarction. In April 1990 under auspices of the Interuniversity Cardiology Institute of the Netherlands, a large nationwide acute intervention trial with captopril in 280 patients receiving thrombolytic therapy was started, the Captopril and Thrombolysis Study (CATS). The primary hypothesis of CATS supposes a very early effect of ACE inhibition on evolving myocardial damage due to ischemia and the consequences of early reperfusion. This will be evaluated by serial echocardiography, Holter monitoring and neurohumoral measurements immediately on thrombolysis and during the first year after myocardial infarction.

Acute effects of the ACE inhibitor lisinopril on cardiac electrophysiological parameters of isolated guinea pig hearts

Angiotensin-converting enzyme (ACE) inhibitors are of benefit in life-threatening ventricular arrhythmias in patients with congestive heart failure and ventricular tachycardia caused by the onset of myocardial ischemia as well as by reperfusion of an ischemic area. The aim of the present study was to investigate whether direct electrophysiological effects are responsible for these observations. Therefore, we investigated the electrophysiological effects of lisinopril on the whole cardiac conduction and pacemaker system in isolated guinea pig hearts perfused by the method of Langendorff at concentrations of 0.01, 0.1, 1, and 10 microM. Lisinopril did not affect heart rate, atrioventricular, His bundle, or intraventricular conduction at any of the concentrations tested. Likewise the frequency-dependent QT duration was unchanged. At a concentration of 10 microM, lisinopril prolonged effective refractory period evaluated by premature beats (46 +/- 15%, n = 8, p less than 0.01) as well as the rate-dependent effective refractory period (31 +/- 12, n = 8, p less than 0.01) of the atrioventricular conduction. These effects can be explained by lisinopril's action as a minor calcium antagonist at a toxic concentration of 10 microM. The present results show that electrophysiological parameters are not substantially altered by lisinopril. Therefore, several other mechanisms such as the unloading of the left ventricle and/or the suppression of noradrenalin release and the electrolyte (potassium and magnesium) repletion and/or regression of left ventricular hypertrophy as long-term effects may play a major role in the antiarrhythmic efficacy of ACE inhibitors.

Beneficial effects of bradykinin on porcine ischemic myocardium

Exogenous bradykinin was administered to pigs in which an experimental infarction was evoked by ischemia and reperfusion. Ischemia (45 min) was induced in a closed-chest model with a balloon catheter in the left anterior descending artery, reperfusion by deflating and removing the balloon. The pigs were treated with saline (n = 11) or bradykinin (0.1 mg/kg in 30 min) infusion (n = 10) during the last 15 min of the ischemic period and the first 15 min of reperfusion. During ischemia, heart rate increased in the saline group to 120 +/- 9% of the initial value (p less than 0.05) and in the bradykinin group to 155 +/- 13% (p less than 0.05). After reperfusion, the rate-pressure product was increased in both groups. The increase of arterial creatine kinase levels was significantly less in the bradykinin-treated group. However, the catecholamine and purine levels were increased, as was the plasma renin activity when compared with the saline group. Two weeks after the infarction, six pigs had died in each group. In three out of five surviving saline-treated pigs and one out of four surviving bradykinin-treated pigs, a sustained ventricular tachyarrhythmia was inducible after programmed electrical stimulation. In conclusion, although systemically administered bradykinin caused a temporary increase in myocardial ischemia, it did reduce the (enzymatic indices of) infarct size. Therefore, the beneficial effects, previously found for ACE-inhibitors might at least partially be related to the potentiation of endogenous bradykinin.

Effect of captopril, an angiotensin-converting enzyme inhibitor, in patients with angina pectoris and heart failure

The effects of captopril and placebo were compared in 18 patients with chronic heart failure and angina pectoris with use of a double-blind crossover trial design. Symptoms were assessed by patient treatment preference, visual analogue scores and nitroglycerin consumption. Exercise performance was assessed using two different treadmill protocols of different work intensity with simultaneous measurement of oxygen consumption and by supine bicycle exercise and simultaneous radionuclide ventriculography. Arrhythmias were assessed by 48 h ambulatory electrocardiographic monitoring. Patients generally preferred placebo to captopril, and this appeared to be due to an increase in symptoms of angina with captopril. Treadmill exercise time on a high intensity protocol was shorter with captopril than with placebo; on a low intensity protocol, angina became a more frequent limiting symptom even though overall exercise performance was not changed. The heart rate-blood pressure product was reduced, but largely because of a reduction in blood pressure rather than in heart rate. During supine bicycle exercise, no differences in symptoms, exercise performance, ejection fraction or changes in blood pressure were noted and ventricular arrhythmias were reduced. Captopril does not appear to be clinically useful in alleviating angina pectoris in patients with heart failure, and this effect may be related to a decrease in coronary perfusion pressure. Nonetheless, desirable metabolic effects, a reduction in arrhythmias and potential effects on survival require further study of captopril in patients with both angina and heart failure.

Post-ischemic release of nucleosides and oxypurines in isolated rat hearts. Possible involvement of ventricular fibrillation

In isolated perfused rat hearts global ischemia for 2, 5, and 15 min was produced. Depending on the duration of the ischemia, postischemic reperfusion led to the release of adenosine and its catabolites, and to more or less severe ventricular tachyarrhythmias. When ventricular fibrillation occurred, a highly significant increase in the purine release was observed compared with non-fibrillating hearts. Prevention of fibrillation by antiarrhythmic drugs decreased the purine release in a highly significant way. After only 2 min of ischemia, reperfusion did not lead to ventricular fibrillation. Electrical induction of fibrillation during the reperfusion in these hearts provoked the release of very high amounts of the purine compounds. A similar effect of electrically-induced fibrillation was also obtained in hearts without a previous ischemic period. The findings suggest that ventricular fibrillation is able to induce the release of purine derivatives from the heart.

ACE inhibitors for the treatment of myocardial ischemia?

Apart from their established use in the treatment of hypertension and heart failure, ACE inhibitors have been suggested to exert anti-ischemic effects. This article reviews the mechanisms of systemic and intracardiac angiotensin formation, as well as its interaction with the bradykinin, the prostaglandin, and the sympathetic nervous system. While high doses of angiotensin can precipitate myocardial ischemia. experimental data on a potential beneficial effect of ACE inhibitors on ischemic myocardial blood flow and function are inconsistent and controversial. Pooling the few available clinical data, several ACE inhibitors may attenuate myocardial ischemia at rest and during exercise. However, a significant fraction of patients does not benefit or even deteriorates. Recent experimental studies suggest a beneficial role of ACE inhibitors in attenuating reperfusion arrhythmias and postinfarction left ventricular remodeling. Unless the mechanisms and determinants of potential anti-ischemic actions of ACE inhibitors can be better defined, their use for treatment of myocardial ischemia cannot be recommended at present.

Cardiac angiotensinogen and its local activation in the isolated perfused beating heart

Increasing evidence suggests that the renin-angiotensin system modulates cardiovascular homeostasis both via its circulating, plasma-borne components and through locally present, tissue-resident systems with site-specific activity. The existence of such a system in the heart has been proposed, based on biochemical studies as well as on the demonstration of renin and angiotensinogen messenger RNA in cardiac tissue. We conducted the present study to determine whether biologically active angiotensin peptides may be cleaved within the heart from locally present angiotensinogen. Isolated, perfused rat hearts were exposed to infusions of purified hog renin; the coronary sinus effluent was collected and subsequently assayed for angiotensin I (Ang I) and angiotensin II (Ang II) by high-pressure liquid chromatography and specific radioimmunoassay. Both Ang I and II were undetectable under control conditions but appeared promptly after the addition of renin. Dose-dependent peak values for Ang I release ranged from 2.42 +/- 0.65 fmol/min to 1.38 +/- 0.18 pmol/min during renin infusions at concentrations between 10 microunits/ml and 5 milliunits/ml. Ang II levels measured in the perfusate reflected a mean fractional intracardiac conversion of Ang I to Ang II of 7.18 +/- 1.09%. Generation of Ang I and Ang II was inhibited in the presence of specific inhibitors of renin and converting enzyme, respectively. To investigate the source of angiotensinogen, we measured spontaneous angiotensinogen release from isolated perfused hearts. In the absence of renin in the perfusate, angiotensinogen was initially released in high, but rapidly declining, concentrations and subsequently at a low, but stable, rate. Prior perfusion with angiotensinogen-rich plasma resulted in enhanced early angiotensinogen release but did not alter the second, delayed phase, suggesting that, in addition to plasma-derived substrate, locally produced angiotensinogen may also participate in the intracardiac formation of angiotensin. Supporting this interpretation, hearts from animals pretreated with dexamethasone showed increased angiotensinogen messenger RNA concentrations as well as increased rates of angiotensinogen release not only during the early but also during the late phase. Our study newly demonstrates that Ang I and II may be formed within the isolated heart from locally present substrate, which appears to be derived in part from the circulating pool and in part from endogenous synthesis. These findings add support to the concept of a functionally active and locally integrated cardiac renin-angiotensin system and emphasize its potential physiological and pathological relevance.

Characterization of cardiac angiotensin converting enzyme (ACE) and in vivo inhibition following oral quinapril to rats

1. Angiotensin converting enzyme (ACE) from the rat heart and lung was studied by use of the radioligand [125I]-351A. 2. Displacement of the bound radioinhibitor [125I]-351A was used to assess the relative potency of six ACE inhibitors in rat heart and lung homogenates and estimate the binding association constant (KA). 3. The KA for atrial preparations was significantly higher than that of the lung (P less than 0.025) and also the ventricles (P less than 0.005). Ventricular preparations and preparations from the lung also differed significantly (P less than 0.05). These differences in KA were noted for all six ACE inhibitors used to displace the radioligand. 4. The rank order of potency of the ACE inhibitors was quinaprilat = benazeprilat greater than perindoprilat greater than 351A greater than lisinopril greater than fosinoprilat. 5. Cardiac ACE inhibition was studied ex vivo following oral administration of quinapril to rats. Following 0.3 mg kg-1 quinapril, the time course and degree of inhibition of ventricular and atrial ACE were similar. 6. These results suggest that the detected differences in KA noted have only a limited potential biological significance. The difference in KA may reflect variations in the structure or conformation of ACE in different tissues.

Individualized antianginal therapy guided by systemic arterial pressure

All antianginal drugs except nitrates are also first-line antihypertensive drugs. Their antianginal efficacy has not been evaluated in relation to pretreatment blood pressure. They may aggravate ischemia due to excessive reduction in blood pressure. Until the results of direct comparative studies are available, it is advisable to start treatment of angina pectoris in normotensive and hypotensive patients with other drugs that do not primarily decrease blood pressure. Nitrates are a reasonable choice.

The effects of oral pretreatment with zofenopril, an angiotensin-converting enzyme inhibitor, on early reperfusion and subsequent electrophysiologic stability in the pig

The effects of oral zofenopril pretreatment were investigated in a chronic closed-chest pig model of ischemia and reperfusion. Pigs (25-35 kg) were pretreated orally with zofenopril (15 mg/day) on the 2 days prior to ischemia, which was evoked by the inflation of a catheter balloon in the left anterior descending coronary artery over 45 minutes. The catheter was then removed and the myocardium was reperfused. After 2 weeks, infarct properties were assessed by signal averaging of the body surface electrocardiogram and the inducibility of malignant ventricular tachyarrhythmias was tested with a programmed electrical stimulation protocol. A significant increase in the pressure-rate product (43 +/- 11%, mean +/- SEM), indicating the oxygen demand of the heart, was prevented by zofenopril (19 +/- 8%, p less than 0.05). Zofenopril reduced the peak efflux of adrenaline (1302 +/- 213 vs. 3201 +/- 760 pg/ml; p less than 0.05), noradrenaline (402 +/- 54 vs. 902 +/- 282 pg/ml; p less than 0.05), and of the adenosine catabolites inosine and hypoxanthine (56 +/- 4 vs. 78 +/- 9, pg/ml; p less than 0.05) in the coronary venous effluent. The efflux of the cytoplasmatic enzyme creatine phosphokinase was not significantly reduced after zofenopril (p = 0.08). No difference in plasma renin levels between the groups were found. After 2 weeks, late potentials were found only in the surviving animals from the untreated group, i.e., the voltage vector magnitude was more reduced, and a prolongation of the QRS duration and of the terminal low-amplitude part of the high-frequency QRS were found.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of ACE inhibitors in the treatment of arrhythmias

Several experimental models have been studied to determine the role of angiotensin-converting enzyme (ACE) inhibitors in reducing ischemic and reperfusion arrhythmias. Studies of left main coronary artery occlusion in isolated perfused rat hearts have shown that the ACE inhibitor captopril reduced reperfusion ventricular fibrillation from 100% to 0% and was associated with a reduction in purine overflow and in norepinephrine release. These effects were abolished in the presence of indomethacin. In an anesthetized rat model of acute myocardial infarction (MI), ACE inhibition reduced mean duration of ventricular fibrillation from 1,133 to 135. ACE inhibition at programmed electrical stimulation of the heart in a closed-chest pig model of acute MI reduced the inducibility of sustained, reproducible ventricular tachycardia from a mean of 42 to 8%. In this model, ventricular tachycardia could not be provoked in animals treated with captopril from the time of acute ischemia. Studies on the rate of ventricular ectopy in patients with poor left ventricular function have demonstrated a significant reduction with ACE inhibition. However, while a protective effect has been shown, the mechanism of action is still speculative.

Tissue renin-angiotensin systems in the heart and vasculature: possible involvement in the cardiovascular actions of converting enzyme inhibitors

The existence of independently functioning local renin-angiotensin systems in a number of tissues has been firmly established by biochemical and functional evidence and, most recently, by the demonstration of genetic messages for components of the renin-angiotensin systems, such as renin and angiotensinogen, in several organs. In this review, local renin-angiotensin systems in the heart and vascular walls are described and the contribution of a local inhibition of converting enzymes to the cardiovascular actions of converting enzyme inhibitors is discussed. Most of the studies cited support the hypothesis that an inhibition of cardiac converting enzyme may be involved in the beneficial hemodynamic and metabolic actions of converting enzyme inhibitors in cardiovascular disease, such as hypertension and congestive heart failure, independent of the circulating renin-angiotensin system. Local effects on cardiac converting enzyme may contribute to the ability of converting enzyme inhibitors to reduce cardiac hypertrophy. Similarly, local converting enzyme inhibition in the vascular wall may not only constitute a mechanism involved in the antihypertensive effects of converting enzyme inhibitors, but may also contribute to the regression of hypertension-induced vascular hypertrophy. In addition to reduced local angiotensin II generation, converting enzyme inhibition may engender a potentiation of the local effects of kinins. This mechanism may be more important to the cardiovascular actions of converting enzyme inhibitors than initially thought.

Issues surrounding a local cardiac renin system and the beneficial actions of angiotensin-converting enzyme inhibitors in ischemic myocardium

Several experimental in vitro and in vivo studies have shown that structurally diverse converting enzyme inhibitors improve contractile dysfunction, as well as reduce arrhythmia production and acute mortality after occlusion of the coronary artery. Biochemical data have demonstrated that some inhibitors of converting enzyme bind better to cardiac angiotensin-converting enzyme (ACE) than others; however, there has not been any demonstrated correlation between inhibition of the enzyme and improvement in cardiac physiology in the acutely dysfunctioning stunned myocardium. It is assumed that ACE inhibitors reduce tissue generation of angiotensin II; however, this relationship as well as peptide levels in coronary venous effluent need to be specifically measured. The multiple substrates of ACE necessitate further work to explore the role of bradykinin and prostacyclin, which have been implicated by some workers as contributing to the beneficial action of ACE inhibitors. A new question is whether sulfhydryl-containing ACE inhibitors are scavengers of toxic free radicals. Captopril, e.g., has been shown to be a free radical scavenger in superoxide-generating systems. Further work is required; however, as one report has recently shown, captopril does not directly scavenge superoxide but acts indirectly as an antioxidant or by altering the concentration of cytochrome c.

Cardiac arrhythmias are ameliorated by local inhibition of angiotensin formation and bradykinin degradation with the converting-enzyme inhibitor ramipril

We investigated the influence of the angiotensin-converting enzyme (ACE) inhibitor ramipril on cardiac arrhythmias in guinea pigs and rats. Ramiprilat, the active moiety of ramipril, did not influence action potentials of isolated guinea-pig papillary muscle or rabbit sinus node, thereby excluding cellular electrophysiological evidence of anti-arrhythmic properties. Ramipril protected against cardiac arrhythmias induced by digoxin infusion in guinea pigs. This effect was comparable with that of lidocaine. In isolated perfused ischemic working rat hearts, angiotensin (ANG) I (3 x 10(-9) M/l) and ANG II (1 x 10(-9) M/l) aggravated reperfusion arrhythmias, accompanied by deterioration of cardiodynamic and metabolic events. Bradykinin (BK) (1 x 10(-10)-1 x 10(-8) M/l), in contrast, protected against reperfusion arrhythmias, which corresponded to an increase in energy-rich phosphates and glycogen stores and a decrease in lactate levels in myocardial tissue. Identical changes were seen in hearts from rats pretreated with ramipril (1 mg/kg PO) or perfused with ramiprilat (2.58 x 10(-7)-2.58 x 10(-5) M/l). Local ACE inhibition in these ischemic hearts antagonized ANG I but not ANG II effects and enhanced BK effects. The BK antagonist D-Arg-(Hyp2, Thi5,8, D-Phe7)BK abolished the beneficial effects of BK, ramipril, and ramiprilat. Increased concentrations of BK or ramiprilat were able to reverse the antagonism. The antiarrhythmic agent nicainoprol, a fast-sodium-channel blocking drug (class Ib), also protected isolated rat hearts against reperfusion arrhythmias, but was without beneficial effects on cardiac hemodynamics and biochemical parameters, in contrast to the ACE inhibitor. These results suggest that the beneficial effects of the ACE inhibitor ramipril on digoxin and reperfusion arrhythmias are not mediated by their direct actions on ionic channels in the cell membrane. It seems that other factors are responsible for its beneficial effects on reperfusion arrhythmias, cardiac function, and metabolism, which are associated with a reduction in ANG II generation and BK degradation by local ACE inhibition in the heart.

Cardiac electrophysiological actions of captopril: lack of direct antiarrhythmic effects

1. Standard microelectrode techniques were used to study the effects of captopril (1, 10 and 100 microM) on action potentials recorded from guinea-pig ventricular cells and sinoatrial node cells. 2. Captopril had no effect on the maximum rate of depolarization (Vmax) of ventricular action potentials in cells exposed to either normal Locke solution or 'simulated ischaemic' solution (K1 11.2 mM; pH-6.4; PO2 less than 80 mmHg), nor was there any augmentation of the normal small decline in Vmax with increasing stimulation rate (range of interstimulus intervals = 2400 ms to 300 ms). 3. Captopril had no effect on the duration of ventricular action potentials, nor did it alter the shortening seen on exposure to simulated ischaemia. 4. Captopril did not alter spontaneous sinus cycle length or any recorded parameter of sinus node action potentials. 5. It is concluded that any antiarrhythmic effects observed during clinical use of captopril are most unlikely to be due to direct actions of the drug on cardiac cell membrane properties.

Angiotensin converting enzyme in the rat heart: studies of its inhibition in vitro and ex vivo

1. The pharmacokinetics of angiotensin converting enzyme (ACE) inhibition in rat heart and lung was evaluated in vitro and ex vivo. 2. Radioinhibitor [125I]-351A binding displacement was used to assess the relative potency of six ACE-inhibitors (CI906, CGS14831, S9780, 351A, MK521, SQ27519) in rat heart and lung homogenates, and estimate equilibrium association constant (Ka). 3. Following oral administration of 0.3 mg/kg of Quinapril (CI928) specific binding of [125I]-351A to ACE was measured in rat heart. 4. Ka for binding to ACE of each inhibitor was significantly higher in right and left atrium than in lung (P less than 0.05) or the right and left ventricle (P less than 0.005). These differences did not affect the degree or time course of inhibition in vivo in the rat myocardial ACE following Quinapril treatment. 5. Rank order of potency of the ACE inhibitors tested was CI906 = CGS14831 greater than S9780 greater than 351A greater than MK521 greater than SQ27519

Aspects of molecular biology and biochemistry of the cardiac renin-angiotensin system

1. Recent evidence for the existence of extrarenal tissue renin-angiotensin systems has raised the question of whether such a system also exists in the heart. 2. Evidence is presented for a cardiac renin-angiotensin system based on molecular biological and biochemical data. In addition, the question of whether the components of this system interact as a locally integrated, biologically functioning unit is addressed. 3. Using radio-labelled cRNA probes prepared from specific cDNA fragments, renin and angiotensin gene expression in atria and ventricles of the rat heart have been documented by Northern blot and liquid hybridization analysis. Relative signal strength for both mRNAs was highest in the atria, followed by the right and left ventricle. 4. Using specific, h.p.l.c.-controlled RIAs for angiotensin peptides, the presence of both angiotensin I and angiotensin II in all anatomical regions of the monkey and rat heart have been demonstrated; similarly, presence of converting enzyme activity was also ascertained by direct in vitro determinations. 5. Additional experiments evaluating the spontaneous release of angiotensin from rat isolated, perfused hearts revealed a bimodal pattern of high, but rapidly declining rates during the first hour (perhaps representing washout of a pool sequestrated from plasma), followed by a prolonged period of steady, low level release, consistent with the secretion of locally synthesized protein. 6. In separate experiments aimed at examining the possible local integration of the components of the cardiac renin-angiotensin system, angiotensin II concentrations were measured in the coronary sinus effluent of rat isolated, perfused hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Captopril improves recovery of adenosine triphosphate during reperfusion of the ischemic isolated rat heart; a 31-phosphorus-nuclear magnetic resonance study

The effect of captopril on energy-rich phosphates and pH during normothermic ischemic arrest, hypothermic cardioplegic arrest and subsequent reperfusion was investigated in the isolated rat heart using 31P-nuclear magnetic resonance. The hearts remained in the probe during all perfusion procedures and captopril (80 ml.l-1) treatment was started directly after cannulation. After normothermic ischemic arrest (15 min), the ATP content of captopril-treated hearts was not significantly different from that of untreated hearts (53 +/- 9% and 52 +/- 8%, respectively). Accumulation of inorganic phosphate at the end of ischemia was significantly less in treated hearts, suggesting a higher end-ischemic nucleotide content in treated hearts. Hypothermic cardioplegic arrest (St. Thomas' Hospital solution, 4 degrees C) lasted for 3 h at 10 degrees C. Adenosine triphosphate in untreated hearts was significantly lower at the end of ischemia; 36 +/- 6% compared to 53 +/- 9% for untreated hearts. Adenosine triphosphate in untreated hearts recovered to 76 +/- 9% after normothermic ischemia and to 72 +/- 7% after hypothermic ischemia at the end of 30 min reperfusion. Captopril significantly improved adenosine triphosphate recovery in both treated groups; 89 +/- 4% after normothermic and 83 +/- 4% hypothermic ischemia. We conclude that captopril has a beneficial effect on recovery of adenosine triphosphate both after normothermic and after hypothermic ischemia.

Effects of nicainoprol on reperfusion arrhythmia in the isolated working rat heart and on ischemia and reperfusion arrhythmia and myocardial infarct size in the anesthetized rat

The effect of the novel antiarrhythmic agent nicainoprol on coronary occlusion and reperfusion arrhythmia was investigated in isolated working rat hearts and in anesthetized rats. In isolated working rat hearts nicainoprol (10(-6) M, 5 X 10(-6) M and 10(-5) M) induced concentration-related protection against reperfusion arrhythmia without changing the cardiodynamics, with the exception of a decrease in heart rate at the highest concentration. Enzyme levels (lactate dehydrogenase and creatine kinase) in the coronary venous effluent, and cardiac tissue concentrations of glycogen, lactate, ATP and creatine phosphate were not affected by nicainoprol. Given to anesthetized rats, nicainoprol (5 and 10 mg/kg i.v.) reduced dose dependently in the early post occlusion (0-30 min) period, the percentage of animals with premature ventricular complexes (PVCs) and ventricular tachycardia while completely preventing the occurrence of ventricular fibrillation. In the reperfusion period no animal treated with 5 mg/kg and 12% of the rats treated with 10 mg/kg showed PVCs (the only form of arrhythmia observed in this period) versus 60% of the control rats. Both doses of nicainoprol induced a decrease in heart rate, blood pressure and myocardial oxygen consumption. The ratio of infarct mass to ventricular mass was significantly reduced by 20% at a dose of 5 mg/kg and by 28% at the dose of 10 mg/kg. Nicainoprol could be useful in the prevention and treatment of arrhythmias associated with acute myocardial infarction.

Pharmacologic approaches to management of arrhythmias in patients with cardiomyopathy and heart failure

Interactions between disordered cardiac rhythm and abnormal cardiac hemodynamic function are well recognized. Demonstrations of this relationship include the relationship between prognostic significance of ventricular ectopy and left ventricular ejection fraction, impairment of ventricular function in association with loss of atrial systole in disease states, increased risk of potentially lethal arrhythmias in the myopathic ventricle, and the evolution of advanced grades of ventricular arrhythmias in acute heart failure. With the development of newer and more potent antiarrhythmic agents, in conjunction with drugs that can improve the failing circulation, it is now possible to clarify these interrelationships and perhaps develop new strategies for clinical management.