Pirbuterol, an oral beta-adrenergic receptor agonist, in the treatment of chronic cardiac failure

Evaluation of antihypertensive activity and molecular docking analysis of Padina boergesenii extract

INTRODUCTION

Antihypertensive drugs that are chemically synthesized usually tend to initiate different health complications. The quest for bioactive molecules to create novel medicines has focused on Marine resources like seaweeds. These molecules can furnish a positive probability for patients to gain benefits from these natural substances.

METHODS

This study aims to identify phytoconstituents present in brown seaweed-Padina boergesenii. Five different solvents were used to prepare extracts and their antioxidant activity as well as antihypertensive activity was evaluated. Phytoconstituents were identified using LC-MS/MS, and subjected to molecular interaction against ACE enzyme.

RESULTS

The 70% ethanolic extract exhibited the highest total phenolic content (TPC), significant radical scavenging activity and concentration dependent Angiotensin Converting Enzyme (ACE) inhibition activity. LC-MS/MS analysis confirmed the presence of bioactive compounds from which 7,8 dihydroxycoumarin had the highest affinity against ACE enzyme in molecular docking study.

CONCLUSION

These findings advocate that Padina boergesenii can be a potential source for developing novel antihypertensive therapeutic drug(s) and could pave the way for evolving effective and safe remedies from natural resources.

Cardiac cachexia: a systematic overview

Cardiac cachexia as a terminal stage of chronic heart failure carries a poor prognosis. The definition of this clinical syndrome has been a matter of debate in recent years. This review describes the ongoing discussion about this issue and the complex pathophysiology of cardiac cachexia and chronic heart failure with particular focus on immunological, metabolic, and hormonal aspects at the intracellular and extracellular level. These include regulators such as neuropeptide Y, leptin, melanocortins, ghrelin, growth hormone, and insulin. The regulation of feeding is discussed as are nutritional aspects in the treatment of the disease. The mechanisms of wasting in different body compartments are described. Moreover, we discuss several therapeutic approaches. These include appetite stimulants like megestrol acetate, medroxyprogesterone acetate, and cannabinoids. Other drug classes of interest comprise angiotensin-converting enzyme inhibitors, beta-blockers, anabolic steroids, beta-adrenergic agonists, anti-inflammatory substances, statins, thalidomide, proteasome inhibitors, and pentoxifylline.

Should acute treatment with inhaled beta agonists be withheld from patients with dyspnea who may have heart failure?

In patients with dyspnea, prehospital and emergency providers make therapeutic decisions before a diagnosis is established. Inhaled beta-2 agonists are frontline treatment for patients with dyspnea due to asthma or chronic obstructive pulmonary disease (COPD) exacerbations. However, these agents have been associated with increased adverse events when administered chronically to heart failure patients. Our goal was to determine the safety and efficacy of acute administration of inhaled beta-2 agonists to patients with heart failure. MEDLINE and EMBASE searches were performed using the terms "beta agonists," "albuterol," "congestive heart failure," and "pulmonary edema." Bibliographies of relevant articles were searched. Only studies addressing acute effects of beta-2 agonists were included for analysis. Twenty-four studies comprising 434 patients were identified that addressed the acute delivery of beta-2 agonists in subjects with heart failure--five studies with inhaled administration and 19 with systemic administration. No study directly evaluated the effects of inhaled beta-2 agonists to patients with acutely decompensated heart failure. Treatment of heart failure patients with beta-2 agonists resulted in transient improvements in pulmonary function and cardiovascular hemodynamics. Only one investigation reported an association between beta-2 agonist use and an increase in malignant dysrhythmias. Investigations in animal models of heart failure and acute lung injury demonstrated resolution of pulmonary edema with beta agonist administration. There is insufficient evidence to suggest that acute treatment with inhaled beta-2 agonists should be avoided in patients with dyspnea who may have heart failure. Based on small studies and indirect evidence, administration of beta-2 agonists to patients with heart failure seems to improve pulmonary function, cardiovascular hemodynamics, and resorption of pulmonary edema. Although an increase in adverse effects with the use of beta-2 agonists cannot be ruled out based on these data, there was no evidence of an increase in clinically significant dysrhythmias, especially when administered by inhalation. Based on these findings, further study should focus on the clinical outcomes of patients with acutely decompensated heart failure who are treated with inhaled beta-2 agonist therapy.

The new compound, LASSBio 294, increases the contractility of intact and saponin-skinned cardiac muscle from Wistar rats

1. A new compound designated as LASSBio 294 (L-294), 3,4-methylenedioxybenzoyl-2-thienylhydrazone, was synthesized as an alternative therapeutic for cardiac dysfunction. 2. L-294 increased in a dose-dependent manner the spontaneous contractions of isolated hearts from Wistar rats with maximal effect (128.0+/-0.7% of control) observed at 25 microM. 3. The positive inotropic effect of L-294 was also observed in electrically stimulated cardiac tissues from Wistar rats. The maximal increment of twitches, at 200 microM, was 163.1+/-18.4% for atrial, 153.5+/-28.5% for papillary and 201.5+/-18.5% for ventricular muscles. 4. In saponin skinned ventricular cells: (a) L-294 present in the period of sarcoplasmic reticulum (SR) loading with Ca(2+) shifted the dose and caffeine-induced contracture curve; (b) L-294 (100 microM) increased 40% the Ca(2+) uptake into SR; (c) L-294 did not significantly alter the sensitivity of contractile proteins to Ca(2+) in SR-disrupted skinned ventricular cells. 5. Retrograde perfusion of the isolated heart from Wistar rats with L-294 (100 microM) did not cause any significant change in rhythm, heart rate (control, 220+/-14.7 b.p.m.; 246+/-24.6 b.p.m. for L-294), PR interval (control, 66.0+/-2.4 ms; 64.0+/-2.3 ms for L-294) or QRS duration (control, 28.8+/-3.4 ms; 32.0+/-2.0 ms for L-294). 6. These results suggest a novel mechanism for a positive cardioinotropic effect through an interaction with the Ca(2+) uptake/release process of the SR. The effect of L-294 could be explained by a pronounced increased accumulation of Ca(2+) into the SR.

Acute effects of a single low oral dose of pimobendan on left ventricular systolic and diastolic function in patients with congestive heart failure

A recent long-term multicenter trial has shown that pimobendan is more effective when administered in low doses. However, no data are available concerning the effect of a low dose of pimobendan on the systolic and diastolic pressure-volume relations in patients with heart failure. Therefore we examined the effects of a single low dose of oral pimobendan, a calcium sensitizer, on systolic and diastolic hemodynamics in patients with cardiomyopathy and congestive heart failure. We measured the left ventricular (LV) pressure-volume relations using a conductance catheter with a micromanometer tip in 10 patients with chronic congestive heart failure resulting from idiopathic cardiomyopathy before and 45 and 90 min after administration of a single oral dose of 2.5 mg of pimobendan. End-systolic elastance was used as an index of LV contractility and was measured during transient occlusion of the inferior vena cava. End-systolic elastance increased significantly by 25% at 45 min (p < 0.05) and by 55% at 90 min (p < 0.01) without an increase in myocardial oxygen consumption. The inotropic effect was accompanied by improved ventriculoarterial coupling. This effect was attenuated in patients with severely impaired myocardial contractility. LV relaxation, assessed by the time constant of isovolumic pressure decay (T(1/2)), was significantly shortened at 90 min (from 47.7 +/- 1.9 to 41.2 +/- 1.7 ms; p < 0.01), although it remained unchanged at 45 min. The diastolic pressure-volume relation showed a leftward and downward shift in all patients. These results indicate that low-dose oral pimobendan had favorable short-term inotropic and lusitropic effects in patients with congestive heart failure caused by idiopathic dilated cardiomyopathy, and may thus be a useful alternative to traditional agents. Further study in a large-scale trial is merited.

Inotropic agents in older patients with chronic heart failure--current perspectives

Until recently, inotropic therapy has been regarded as the most direct remedy for the left ventricular systolic dysfunction that often underlies the development of heart failure. Nevertheless, all the agents with significant inotropic properties that have been evaluated to date (such as beta adrenergic stimulants, phosphodiesterase inhibitors, and high-dose vesnarinone) showed significant increases in mortality with long-term administration. However, it is noteworthy that the participants in trials to evaluate inotropic therapy were not representative of geriatric heart failure patients for age, gender, and comorbidity. Thus, results from these studies must be interpreted cautiously when treatment for chronic heart failure must be applied to elderly subjects. At present, digitalis is the only inotropic agent recommended for long-term treatment, because it improves symptoms and prevents disease progression through neurohormonal and baroreceptor mechanisms; nevertheless, its long-term safety is still undetermined. The role of low-dose vesnarinone, pimobendan and ibopamine, which share neurohormonal, rather than inotropic, mechanisms of action, is still under investigation. Pending the definition of these issues, ACE-inhibitors and diuretics remain the mainstay of therapy for chromic heart failure.

The development of positive inotropic agents for chronic heart failure: how have we gone astray?

Because cardiac contractility is impaired in chronic heart failure, many pharmacologic agents have been developed to increase the contractile state of the failing heart. These drugs produce impressive hemodynamic effects, but long-term therapy has failed to produce clinical benefits and has increased mortality in treated patients. This experience has led many physicians to suggest that positive inotropic therapy be abandoned as a therapeutic approach for heart failure. However, recent studies suggest that the efficacy and safety of many (if not all) positive inotropic drugs can be greatly enhanced by reducing the dose of these drugs. The importance of dose is dramatically illustrated by the results of trials with vesnarinone, which decreases mortality when used in low doses but increases mortality when administered in doses only twice as large. Although low doses of positive inotropic drugs may be clinically superior to high doses, it is not clear that these low doses exert significant inotropic effects. All positive inotropic drugs exert actions on the circulation in addition to stimulating the heart, and these ancillary properties may be particularly important at low doses of these drugs. Low doses of milrinone and pimobendan may act primarily to dilate peripheral blood vessels; low doses of digitalis may exert only neurohormonal effects, and low doses of vesnarinone may act as an antiarrhythmic agent. If the noninotropic actions of low doses account for the therapeutic benefits of these drugs, then the positive inotropic effects seen at high doses may be primarily responsible for their adverse effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibition, the sympathetic nervous system, and congestive heart failure. The Australian Zestril (Lisinopril) Study Group

Catecholamines have been found to be powerful indicators of prognosis in patients with congestive heart failure. However, it is uncertain whether catecholamines are a marker for decreased cardiac performance or part of the pathologic process. Catecholamines, exogenously derived beta-adrenergic stimulants, and drugs that amplify sympathetic responsiveness produce early hemodynamic benefits, but do not appear to provide long-term improvement in terms of symptoms or exercise tolerance, whereas blockade of the beta-adrenoceptor appears to have little early benefit but may improve long-term prognosis. This suggests that in the long term, increased catecholamine levels may be deleterious. Angiotensin-converting enzyme (ACE) inhibitors can modulate circulating catecholamines, and the persistence and degree of ACE inhibition may be important not only in reducing catecholamines, but possibly also in reducing mortality in heart failure. It appears that ACE inhibitors definitely reduce mortality in congestive heart failure. It remains to be documented whether the persistence and degree of ACE inhibition is a factor in this effect, and, thus, comparison of short- with long-acting ACE inhibitors and study of the dosage of ACE inhibitors are of importance. The extent to which modulation of the sympathetic nervous system by ACE inhibitors is an important mechanism in their effect in reducing mortality remains to be established.

Effect of oral milrinone on mortality in severe chronic heart failure. The PROMISE Study Research Group

BACKGROUND

Milrinone, a phosphodiesterase inhibitor, enhances cardiac contractility by increasing intracellular levels of cyclic AMP, but the long-term effect of this type of positive inotropic agent on the survival of patients with chronic heart failure has not been determined.

METHODS

We randomly assigned 1,088 patients with severe chronic heart failure (New York Heart Association class III or IV) and advanced left ventricular dysfunction to double-blind treatment with (40 mg of oral milrinone daily (561 patients) or placebo (527 patients). In addition, all patients received conventional therapy with digoxin, diuretics, and a converting-enzyme inhibitor throughout the trial. The median period of follow-up was 6.1 months (range, 1 day to 20 months).

RESULTS

As compared with placebo, milrinone therapy was associated with a 28 percent increase in mortality from all causes (95 percent confidence interval, 1 to 61 percent; P = 0.038) and a 34 percent increase in cardiovascular mortality (95 percent confidence interval, 6 to 69 percent; P = 0.016). The adverse effect of milrinone was greatest in patients with the most severe symptoms (New York Heart Association class IV), who had a 53 percent increase in mortality (95 percent confidence interval, 13 to 107 percent; P = 0.006). Milrinone did not have a beneficial effect on the survival of any subgroup. Patients treated with milrinone had more hospitalizations (44 vs. 39 percent, P = 0.041), were withdrawn from double-blind therapy more frequently (12.7 vs. 8.7 percent, P = 0.041), and had serious adverse cardiovascular reactions, including hypotension (P = 0.006) and syncope (P = 0.002), more often than the patients given placebo.

CONCLUSIONS

Our findings indicate that despite its beneficial hemodynamic actions, long-term therapy with oral milrinone increases the morbidity and mortality of patients with severe chronic heart failure. The mechanism by which the drug exerts its deleterious effects is unknown.

Effects of xamoterol on inotropic and lusitropic properties of the human myocardium and on adenylate cyclase activity

The purpose of the present study was to characterize the effects of xamoterol in the human myocardium. In the presence of forskolin or milrinone, xamoterol increased isometric force of contraction, contraction velocity, and relaxation velocity in isolated, electrically driven preparations from human myocardium, but had no effect alone. There was no difference in the effect of xamoterol between right atrial myocardium and left ventricular myocardium from nonfailing (NF), moderately failing (NYHA II-III), and severely failing (NYHA IV) human hearts. The positive inotropic and lusitropic effects of isoprenaline were reduced depending on the severity of heart failure in left ventricular myocardium (i.e., NF greater than NYHA II-III greater than NYHA IV). In the presence of norepinephrine, xamoterol produced negative inotropic effects similar to those of the beta-adrenoceptor antagonists pindolol and propranolol. Xamoterol alone had no effects on force of contraction, whereas pindolol and propranolol markedly reduced contractile force. In NYHA class IV, isoprenaline stimulated adenylate cyclase about twofold but xamoterol, like pindolol or propranolol, had no effect. Experiments with the beta 1- and beta 2-selective antagonists CGP 207.12A and ICI 118.551, respectively, showed that the positive inotropic and lusitropic effects of xamoterol were mediated by beta 1-adrenoceptors. Consistently, xamoterol had a selectivity of 13.8 at beta 1-adrenoceptors as measured in radioligand binding experiments. It is concluded that xamoterol acts as a beta 1-adrenoceptor antagonist with a selectivity of 13.8 in human ventricular myocardium. The compound has an intrinsic sympathomimetic activity, as it produces beta 1-adrenoceptor-mediated positive inotropic and lusitropic effects in the presence of forskolin. The beneficial effects of xamoterol in patients with heart failure could be due to prevention of the detrimental effects of norepinephrine such as beta 1-adrenoceptor downregulation of an increase of Gi (inhibitory guanine-nucleotide binding protein).

Medical management of chronic heart failure: inotropic, vasodilator, or inodilator drugs?

On the basis of pathophysiologic mechanisms, the medical therapy of today for chronic heart failure is reviewed. The advantages and disadvantages of the vasodilator drugs and the inotropic drugs are presented. Finally, the therapeutic value of the inodilator drugs, which combine the central myocardial effects of positive inotropic agents with those of peripheral vasodilators, is discussed. In particular, the orally available dopaminergic agents, such as ibopamine, which interact with beta-receptors in the heart (mediating a positive inotropic effect) as well as with dopaminergic receptors in the peripheral vessels (mediating a systemic vasodilator effect) and in the kidneys (potentiating the natriuretic effect of diuresis), seem to be an advancement in the modern medical therapy of chronic heart failure. Data are shown during long-term treatment with ibopamine, in which the sustained clinical benefit in heart failure was not diminished, despite a decrease of the adrenergic receptors in blood cells. Dopamine plasma concentration was permanently normalized during long-term treatment. The discrepancy between clinical improvement and the measured adrenergic downregulation may be due to the interference of the inodilator with neurohormonal systems at multiple sites and is probably independent of receptor activation. It is suggested that the biosynthesis of noradrenaline is improved by increasing intracellular dopamine transport.

[Alterations of the cAMP-adenylate cyclase system in the failing human heart. Consequences for the therapy with inotropic drugs]

In heart failure, an increase in the activity of the sympathetic nervous system takes place to maintain perfusion pressure to vital organs, resulting in increased levels of noradrenaline in the blood of these patients. This permanent stimulation produces a down-regulation of cardiac beta-adrenoceptors. Since noradrenaline acts primarily on the cardiac beta 1-adrenoceptor subtype, beta 1-adrenoceptors decrease in number, whereas the beta 2-adrenoceptor subpopulation remains unchanged in most instances. Consequently, the positive inotropic response to beta-adrenoceptor agonists is diminished. However, there is also a decrease in the positive inotropic effect of beta 2-adrenoceptor agonists, histamine and cAMP-phosphodiesterase inhibitors such as milrinone, whereas the positive inotropic effect of cAMP-independent Na(+)-channel activators such as DPI 206-106 and the effects of cardiac glycosides are not diminished. These observations suggest a more generalised alteration of the cAMP-adenylate cyclase system in the failing heart. Stimulatory guanine nucleotide-binding protein (Gs) couples receptors to adenylate cyclase that stimulate cAMP formation, such as beta-adrenoceptors, histamine receptors and glucagon receptors. In the failing human heart, Gs content has been reported to remain unchanged as compared with that in non-failing myocardium. However, there is a 35%-40% increase in inhibitory guanine nucleotide-binding proteins (Gi), which are involved in the receptor-mediated inhibition of adenylate cyclase. Taken together, two defects of the cAMP-adenylate cyclase system have been identified: an increase in Gi content and a decrease in the number of beta-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

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

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

The use of inotropic agents in acute and chronic congestive heart failure

This article reviews our current understanding of the physiology of myocardial contraction; recent research into its mechanical, macromolecular, and biochemical foundations; and its role in the clinical syndromes of congestive heart failure. This review serves as a background for discussing the mechanism of action and pharmacology of currently available and experimental inotropic agents. The clinical applications of these drugs are discussed and the successes and failures of the pharmacologic approach to patients with congestive heart failure analyzed.

Vasodilator and inotropic drugs for the treatment of chronic heart failure: distinguishing hype from hope

During the past 10 years, more than 80 orally active vasodilator and inotropic agents have been tested in the clinical setting to evaluate their potential utility in the treatment of chronic heart failure. Although the initial reports of all of these drugs suggested that each represented a major therapeutic advance, only three agents--digoxin, captopril and enalapril--have produced consistent long-term hemodynamic and clinical benefits in these severely ill patients. Most of the other drugs that have been tested have not (to date) distinguished themselves from placebo therapy in large-scale, controlled trials, even though these agents produce hemodynamic effects that closely resemble those seen with digitalis and the converting-enzyme inhibitors. These observations suggest that the hemodynamic derangements that characteristically accompany the development of left ventricular dysfunction cannot be considered to be the most important pathophysiologic abnormality in chronic heart failure. Although cardiac contractility is usually depressed in this disease, positive inotropic agents do not consistently improve the clinical status of these patients. Similarly, although the systemic vessels are usually markedly constricted, drugs that ameliorate this vasoconstriction do not consistently relieve symptoms, enhance exercise capacity or prolong life. Hence, correction of the central hemodynamic abnormalities seen in heart failure may not necessarily provide a rational basis for drug development, and future advances in therapy are likely to evolve only by attempting to understand and modify the basic physiologic derangements in this disorder.

An introduction to the pharmacologic properties of Dopacard (dopexamine hydrochloride)

Dopexamine hydrochloride (Dopacard) has been developed as a peripherally acting dopamine receptor agonist with afterload reducing properties for use in the acute management of low cardiac output states. Dopexamine hydrochloride is one-third as potent as dopamine in stimulating DA1 receptors but 60 times as potent as a beta 2-adrenoceptor agonist. Unlike dopamine, it is a weak beta 1-adrenoceptor agonist and does not stimulate vascular alpha adrenoceptors. Its stimulant properties at vascular DA1 receptors and at vascular beta 2 adrenoceptors endow it with the ability to improve renal blood flow and to increase cardiac output secondary to afterload reduction. In addition, mild positive inotropic activity arises from stimulation of cardiac beta 2 adrenoceptors, potentiation of endogenous norepinephrine due to uptake-1 blockade, and activation of the baroreceptor reflex. Other features of dopexamine hydrochloride that should enhance its clinical use are lack of arrhythmogenicity and rapid responsiveness to alterations in infusion rate.

Effect of drug therapy on survival in chronic congestive heart failure

A review of the current evidence on the effects of various agents on survival among patients with congestive heart failure (CHF) suggests that angiotensin-converting enzyme inhibitors probably offer the greatest potential for benefit. Trials undertaken before the Cooperative North Scandinavian Enalapril Survival Study (CONSENSUS) revealed favorable trends among patients in New York Heart Association functional classes II to IV who received angiotensin-converting enzyme inhibitors. Data from CONSENSUS clearly demonstrate that enalapril reduces mortality rates among patients in New York Heart Association class IV, but conclusions regarding effects in patients with mild or moderate CHF must await the results of future studies. In contrast, the large data base on alpha-adrenergic blockers suggests that these drugs are not likely to improve survival. Information on inotropic agents is sparse, but it is possible that these drugs may not improve survival and, in fact, may have a harmful effect. Mortality data on CHF patients treated with beta blockers and calcium channel blockers are likewise limited; conclusions concerning effects on survival must be postponed until further studies are conducted. Many of the investigations undertaken thus far to examine survival in patients with CHF have been small and of short duration, so any comparisons of the effects of various drugs must be interpreted with caution.

Piroximone (MDL 19,205) in the treatment of unstable and stable chronic cardiac failure

The hemodynamic and clinical response to oral and intravenous piroximone was examined in 25 patients with chronic cardiac failure secondary to ischemic or myopathic heart disease: 14 with severe failure, who were clinically unstable (group I), and 11 with stable failure of mild to moderate severity (group II) in whom maximal O2 uptake (VO2 max) to treadmill exercise could be monitored serially. Intravenous (0.5 to 1.0 mg/kg) and oral (0.7 to 4.9 mg/kg) piroximone significantly (p less than 0.05) improved right and left ventricular pump function in both groups while causing an insignificant rise in heart rate and reduction in arterial pressure. Myocardial O2 uptake was not altered acutely or subacutely after piroximone, and myocardial lactate production was not observed. The salutary hemodynamic response to oral piroximone was sustained for 5 hours and there was no evidence of tolerance to the third and fourth doses. In group II, VO2 max was increased (p less than 0.05) at 4, 8, 12, 24, and 48 weeks of oral piroximone therapy. Adverse gastrointestinal effects were observed in two patients and a supraventricular tachycardia in another. Thus, piroximone may prove useful in the long-term management of chronic cardiac failure. Controlled clinical trials should be undertaken to determine the ultimate efficacy and safety of piroximone in these patients.

Newer positive inotropic agents in the treatment of chronic cardiac failure. Current status and future directions

Heart failure is a serious worldwide health problem of major proportions. For many physicians, digitalis (an inotropic agent of limited proportions) and diuretics have proven the standard of treatment for heart failure. Vasodilators have also gained acceptance in recent years. Nevertheless, many patients remain symptomatic and therefore attention has been given to the development of pharmacological agents with mechanisms of action targeted to cardiac and vascular smooth muscle. The newer generation of inotropic agents have clearly been shown to improve the pumping function of the failing heart in patients who remain symptomatic despite digitalis, diuretics and vasodilators, while myocardial oxygen consumption is not enhanced. Several uncontrolled trials with the phosphodiesterase inhibitors enoximone, milrinone and piroximone have concluded that these agents improve exercise capacity and thereby hold promise to enhance quality of life. Large scale controlled trials currently in progress will determine the ultimate efficacy, as well as safety, of these agents. Results to date with several orally active beta-adrenoceptor agonists suggest that their efficacy may be limited by the induction of ventricular arrhythmias.

Measurement and interpretation of maximal oxygen uptake in patients with chronic cardiac or circulatory failure

Rapidly responding gas analyzers have simplified the monitoring of oxygen uptake (VO2) in the clinical exercise laboratory. An incremental, exhaustive, upright exercise test can be safely used to determine the plateau in oxygen uptake during exercise, or maximal VO2 (VO2max), in patients with chronic cardiac or circulatory failure. We define VO2max in these patients as an increase in VO2 of less than 1 ml/min/kg despite an increment in work load. The value for VO2max indicates the patient's aerobic capacity; it also predicts the maximal cardiac output during exercise and therefore serves as an estimate of cardiac reserve and of the severity of cardiac or circulatory failure. Symptom-limited VO2 during exercise, termed maximum oxygen uptake but more appropriately peak VO2, bears no relationship to VO2max. The two terms should not be used interchangeably.

Enoximone (MDL 17,043) for stable, chronic heart failure secondary to ischemic or idiopathic cardiomyopathy

To examine the efficacy and safety of enoximone for treatment of patients with chronic, clinically stable cardiac failure secondary to ischemic or myopathic heart disease, 31 patients were enrolled into an early phase II trial. The hemodynamic response to intravenous and oral enoximone was assessed and compared with the response to dobutamine therapy (5 to 10 micrograms/kg/min). Maximal O2 uptake, an objective measure of effort tolerance, was serially monitored. Intravenous (1 to 2 mg/kg) and oral (1 to 2 mg/kg) enoximone improved (p less than 0.05) cardiac index while reducing right atrial and wedge pressures to a greater extent than dobutamine. The salutary hemodynamic response to oral enoximone was sustained for 6 to 8 hours and was not associated with subacute drug tolerance. Maximal O2 uptake was increased (p less than 0.05) at 2, 4, 8, 12, 24 and 52 weeks of oral enoximone therapy (1.4 +/- 0.5 mg/kg every 8 hours) while radionuclide ejection fraction at 65 weeks increased (p less than 0.05) from baseline (39 +/- 16% vs 30 +/- 9%). Nine patients, 8 of whom were in functional class III or IV on enrollment, died after a mean of 18 weeks: 4 from cardiac failure and 5 suddenly. Two patients had adverse gastrointestinal effects. Oral enoximone (1 to 2 mg/kg every 8 hours) appears to be useful in the short- and long-term management of clinically stable, chronic cardiac failure. Controlled phase III trials are warranted.

Adverse effects associated with the newer inotropic agents

The ideal inotropic agent should be available for both parenteral and oral administration and be potent and effective long term without significant adverse effects. In recent years, numerous new agents have been developed in an attempt to find a more potent, less toxic alternative to digoxin. beta-Agonists, while useful when given parenterally short term, appear to have their long term oral application limited by adverse effects and the development of tolerance. A number of other non-catecholamine agents, most of which have both inotropic and vasodilator actions, have also been studied. Adverse effects have been relatively frequent and occasionally severe. Of these newer agents none has yet been proven in clinical trials to be safe and effective in the long term.

Digitalis and other positive catecholamine-like inotropic agents in the management of congestive heart failure

Positive inotropic agents are used to improve the impaired cardiac contractility that characterizes chronic heart failure. Digitalis is the traditional drug given for this purpose. However, there is controversy about the effectiveness of digitalis in chronic heart failure. Analysis of the available data indicates the efficacy of digoxin in mild heart failure (i.e., New York Heart Association functional classes I and II) and the relative lack of efficacy in advanced heart failure (i.e., NYHA functional class IV). Further, digoxin can be stopped in a substantial number of patients without recurrence of congestive heart failure. In selected patients whose condition no longer responds to digoxin, the long-term administration of dobutamine may be an effective alternative approach.

Milrinone in the treatment of chronic cardiac failure: a controlled trial

This study examines the acute hemodynamic response to intravenous and oral milrinone in 12 patients with moderate to moderately severe heart failure. The patients received milrinone or placebo at random in an 8-week double-blind trial. Dosing level and schedule were determined by the hemodynamic results. Acute and chronic plasma samples for milrinone concentration were drawn from patients throughout the study. Milrinone was administered intravenously in successive doses of 25, 50, and 75 micrograms/kg. This resulted in a 16.5%, 12.5%, and 28.4% peak increase in cardiac index, with a concomitant 24%, 29%, and 38% decrease in pulmonary capillary wedge pressure. There were no significant relationships between any of the mean maximal hemodynamic values and milrinone plasma concentration. Six patients received milrinone and six patients received placebo; only five patients completed the blinded phase. There was no significant difference between the groups in exercise capacity, but the conditions of five of the six patients who received placebo deteriorated. In two of the patients who received milrinone the aerobic capacity improved greater than 2 cc/min/kg over baseline, and an additional two patients reported a marked subjective improvement. The results of this study indicate that oral milrinone in the management of patients with chronic cardiac failure would justify larger controlled studies.

Lactate production during maximal and submaximal exercise in patients with chronic heart failure

In patients with chronic heart failure whose cardiac output response to exercise is impaired, determination of anaerobic threshold may provide a useful and objective approach to grade the severity of heart failure. In such patients performing upright treadmill exercise to exhaustion, this study examined the reproducibility of the response of cardiac output and mixed venous lactate concentration when the exercise test was repeated the same or next day, the nature of this response after rest and exercise cardiac output levels were augmented by the cardiotonic agent amrinone and the response of lactate during symptom-limited submaximal exercise performed at either aerobic or anaerobic levels of work for each patient. Findings were: 1) the response of cardiac output and mixed venous lactate was reproducible (p less than 0.05) when assessed either the same or the next day; 2) when exercise cardiac output was increased (p less than 0.05) by oral amrinone therapy, the increase in lactate was delayed (p less than 0.05) to higher levels of muscular work and this was not true when cardiac output was unchanged; and 3) only submaximal anaerobic exercise was symptom limited and associated with an increase in lactate concentration. Thus, the lactate response and anaerobic threshold determination should prove useful to assess the severity of chronic stable heart failure and its response to pharmacologic intervention. The submaximal anaerobic exercise test may provide additional insights into the effort intolerance these patients experience.

Pirbuterol. A preliminary review of its pharmacological properties and therapeutic efficacy in reversible bronchospastic disease

Pirbuterol is a beta-adrenoceptor agonist which differs structurally from salbutamol in the substitution of a pyridine ring for the benzene ring. In common with salbutamol, pirbuterol demonstrates both bronchodilatory and cardiovascular effects. Generally, improvements of up to 25% are noted in forced expiratory volume in 1 second (FEV1) [versus baseline or placebo] in asthmatic patients treated with pirbuterol for several months. In individual 12-week double-blind comparative studies, pirbuterol aerosol appeared similar to orciprenaline (metaproterenol) aerosol, and orally administered pirbuterol appeared similar to orally administered salbutamol in bronchodilator efficacy. However, well-designed long term comparative studies are needed to more clearly define the comparative efficacy of pirbuterol and alternative beta-adrenoceptor agonists.

The effects of dopexamine on the cardiovascular system of the dog

The cardiovascular effects of dopexamine and dopamine were compared in the anaesthetized and conscious dog by the use of intravenous infusions over the dose range 3 X 10(-9) - 10(-7)mol kg-1 min-1. In the anaesthetized dog, dopexamine produced a dose-related fall in blood pressure due to peripheral vasodilatation and a small rise in heart rate and contractility. By contrast, dopamine did not significantly reduce blood pressure but produced a larger dose-related increase in contractility. At the highest infusion rate (10(-7)mol kg-1 min-1) blood pressure and heart rate were increased by dopamine. Dopexamine dilated the renal and mesenteric vascular beds with a potency similar to that of dopamine. Femoral vascular responses produced by both agents were inconsistent but the highest infusion rate of dopamine did produce vasoconstriction. With the aid of selective receptor antagonists (haloperidol, propranolol and bulbocapnine) the vasodepressor activity of dopexamine was shown to be mediated by stimulation of DA2-, beta- and DA1-receptors. The cardiac stimulation and renal vasodilatation produced by both compounds were due to stimulation of beta-adrenoceptors and DA1-receptors respectively. In the conscious dog, intravenous infusion of dopexamine caused a dose-related fall in blood pressure, renal vasodilatation and an increase in cardiac contractility and heart rate. Dopamine also increased cardiac contractility, and renal blood flow due to renal vasodilatation but without affecting heart rate. At the highest infusion rate, blood pressure was increased. Dopexamine and dopamine produced a similar incidence of panting and repetitive licking at 3 X 10(-8)mol kg-1 min-1 and emesis at 10(-7)mol kg-1 min-1, due to stimulation of dopamine receptors in the chemoreceptor trigger zone. Dopexamine produces a different cardiovascular profile from dopamine in the anaesthetized and conscious dog. Both compounds reduce renal vascular resistance, but in contrast to dopamine, dopexamine reduces afterload and produces only mild inotropic stimulation. These differences reflect contrasting activity at adrenoceptors.

Dopexamine: a novel agonist at peripheral dopamine receptors and beta 2-adrenoceptors

Dopexamine is an agonist at peripheral dopamine receptors and at beta 2-adrenoceptors. Dopexamine has approximately one-third the potency of dopamine in stimulating the vascular DA1-receptor in the dog, resulting in a fall in renal vascular resistance of 20% at 2.3 X 10(-8) mol kg-1 (i.a.). Prejunctional DA2-receptors are also stimulated by dopexamine, resulting in a reduction of neurogenic vasoconstriction in the rabbit isolated ear artery (IC50 of 1.15 X 10(-6)M) and of neurogenic tachycardia in the cat (ID50 of 5.4 X 10(-8) mol kg-1, i.v.), with a potency six and four times less respectively than that of dopamine. By contrast, dopexamine is approximately 60 times more potent than dopamine as an agonist at the beta 2-adrenoceptor of the guinea-pig isolated tracheal chain, with an EC50 of 1.5 X 10(-6)M. Both dopexamine and dopamine are weak agonists at the guinea-pig atrial beta 1-adrenoceptor over the concentration range 10(-7) to 10(-4) M, but dopexamine has an intrinsic activity of only 0.16 relative to dopamine. Dopexamine does not stimulate postjunctional alpha 1- or alpha 2-adrenoceptors in the canine isolated saphenous vein, whereas dopamine is an agonist, approximately 120 times less potent than noradrenaline. Unlike dopamine and salbutamol, dopexamine does not cause arrhythmias in the guinea-pig isolated perfused heart at doses of up to 10(-5) mol, which is a thousand times the minimum cardiostimulant dose. The combination of agonist properties at peripheral dopamine receptors and at beta 2-adrenoceptors, with little or no activity at alpha- and beta 1-adrenoceptors gives dopexamine a novel pharmacological profile. This may confer advantages over dopamine in the treatment of acute heart failure.

Detrimental arrhythmogenic and sustained beneficial hemodynamic effects of oral salbutamol in patients with chronic congestive heart failure

The long-term efficacy and potential side effects of oral sympathomimetic amines in the treatment of advanced congestive heart failure remain controversial. We studied the acute and chronic hemodynamic and arrhythmogenic effects of the beta-2 agonist, salbutamol, 6 mg by mouth four times/day, in 20 patients with NYHA classes III to IV congestive heart failure. Acutely, salbutamol increased the cardiac index (1.9 to 2.3 L/min/m2, p less than 0.01) and heart rate (92 to 97 bpm, p less than 0.01) while it decreased pulmonary capillary wedge pressure (35 to 31 mm Hg, p less than 0.01). Salbutamol increased the number of patients having episodes of ventricular tachycardia from two to six and increased the number of episodes of ventricular tachycardia from 2 to 27. Once salbutamol was discontinued, no further episodes of ventricular tachycardia occurred in these six patients. Six patients did not have long-term hemodynamic studies because of serious arrhythmias and two died. In the 12 patients who had long-term studies, the initial beneficial hemodynamic effects of salbutamol were maintained. Thus, although salbutamol may have beneficial long-term hemodynamic effects, it may cause serious arrhythmias in patients predisposed to develop arrhythmias.

Prognosis and treatment of cardiomyopathy and myocarditis

Dilated cardiomyopathy is a heterogeneous group of disorders with a prognosis that is dependent upon the severity of presenting clinical and hemodynamic abnormalities. Although this condition is characterized by a high mortality, spontaneous improvement is noted in 25% of cases. Standard therapeutic modalities are nonspecific and consist of the therapy of congestive heart failure and ventricular arrhythmia. Recent studies suggest that beta blockade and cardiac transplantation may soon become accepted modalities in this condition. Acute viral myocarditis is a common disease that has a good prognosis, however occasionally progression to chronic myocardial disease has been identified. The therapy of acute viral myocarditis should be limited to symptomatic treatment, anti-coagulation, and bed rest. When chronic myocarditis is identified on endomyocardial biopsy in patients with heart failure of unknown cause, the treatment differs little from that of dilated cardiomyopathy with the exception that recognizing that efficacy has not been proven; immunosuppressive therapy may be added in life-threatening situations. Future studies will be directed at further clarification of the prognosis of each of these conditions with intensive evaluation of the role of beta blockade and immunosuppression.

Cardiopulmonary exercise testing for evaluation of chronic cardiac failure

The heart, lungs and hemoglobin form the body's gas transport system, which links the atmosphere and its supply of O2 with tissue, while simultaneously providing for the elimination of the metabolic end-product, CO2, into the atmosphere. The transport of these respiratory gases must be in accordance with metabolic need. This is particularly evident during the physiologic stress of isotonic exercise, when the O2 requirements and CO2 production of skeletal muscle are increased. The monitoring of these respiratory gases during exercise, referred to as cardiopulmonary exercise testing (CAR-PET), can be used to assess heart and lung function in patients with cardiovascular or lung disease or both. Chronic cardiac failure (CCF) may be defined in physiologic terms as that circumstance in which the heart fails to provide tissue with O2 at a rate commensurate with aerobic requirements. In patients with CCF, CAR-PET represents a noninvasive means to determine aerobic capacity (that is, maximal O2 uptake) and anaerobic threshold during incremental treadmill exercise. It can also provide an objective measure of the severity of failure, the functional status of the patient and the heart's pump reserve. By using additional measurements of ventilation, arterial O2 saturation and, in selected cases, hemodynamic monitoring, the nature and severity of cardiovascular and pulmonary disease may be evaluated.

Pharmacology and inotropic potential of forskolin in the human heart

We evaluated the effects of the diterpene compound forskolin in human myocardial adenylate cyclase preparations, isolated trabeculae and papillary muscles derived from failing human hearts, and acutely instrumented dogs. Forskolin was a potent, powerful activator of human myocardial adenylate cyclase and produced maximal effects that were 4.82 (normally functioning left ventricle) and 6.13 (failing left ventricle) fold greater than isoproterenol. In contrast to isoproterenol, forskolin retained full activity in membrane preparations derived from failing hearts. In cyclase preparations, forskolin demonstrated unique substrate and Mg2+ kinetic properties that could be distinguished from hormone receptor-coupled agonists or fluoride ion. The adenylate cyclase stimulatory effect of forskolin was synergistic with isoproterenol, apparently due to the location of forskolin activation being beyond the level of hormone receptor-agonist in the receptor-cyclase complex. Forskolin was a potent positive inotrope in failing human myocardium, producing a stimulation of contraction that was similar to isoproterenol. Finally, in open chest dogs forskolin was a positive inotropic agent that reduced preload and afterload. We conclude that forskolin belongs to a class of agents that may have therapeutic potential in the treatment of congestive heart failure.

Amrinone in the treatment of chronic cardiac failure

The efficacy and safety of oral amrinone were examined in 17 patients with moderately severe to severe heart failure that was refractory to standard medical therapy and vasodilators. The short-term and 28 week response to open amrinone therapy was assessed first, followed by a placebo-controlled, double-blind withdrawal study of two 13 week stages in nine patients. Rest and exercise ventricular function were determined before and after 32 hours of amrinone; aerobic capacity was serially assessed. After 2 hours, 1.64 mg/kg amrinone produced a 40% (p less than 0.001) increase in cardiac output and a 32% (p less than 0.02) decrease in pulmonary wedge pressure without altering heart rate or blood pressure. The exercise cardiac index-wedge pressure curve obtained 32 hours after the first oral dose was significantly shifted (p less than 0.05) above control values. A sustained improvement in maximal oxygen uptake was noted during long-term open amrinone therapy. Subsequently, seven of the patients randomized to placebo therapy had a significant deterioration of symptoms or exercise tolerance, or both. After 4 weeks of readministration of amrinone, clinical stability was once again established and exercise tolerance was improved by Weeks 8 to 16. Adverse effects of thrombocytopenia (one patient) and hepatic dysfunction (one patient) attributable to amrinone were observed. It is concluded that amrinone is effective in the long-term treatment of chronic cardiac failure.