Haemodynamic effects of a new beta 1-receptor agonist in acute myocardial infarction. A useful antidote to unwanted cardiac effects of beta-blocking agents

Haemodynamic effects of intravenously administered prenalterol in patients with severe heart failure

The acute haemodynamic effects of prenalterol 75-225 micrograms/kg i.v. were studied at rest and during exercise in the supine position in 12 patients with chronic congestive heart failure secondary to myocardial infarction (6 pts), chronic valvular disease with valvular replacement (4 pts), ischaemic cardiomyopathy (1 pt) and post myocarditis (1 pt). In 5 of the 6 AMI patients the effect of prenalterol on myocardial oxygen consumption at rest was measured. Pulmonary artery end-diastolic pressure decreased significantly from 17 to 10 mm Hg at rest and from 31 to 21 mm Hg during exercise. Resting heart rate increased from 78 to 90 at rest but was unchanged during exercise. MVO2 in the 5 patients was unchanged or lower in 4 patients and increased in one in whom angina developed after prenalterol. In general, dyspnoea and angina during exercise were less pronounced after prenalterol. The calculated triple product was lower after prenalterol, especially during exercise, indicating lower myocardial oxygen consumption and probably less myocardial ischaemia.

Effects of prenalterol administered orally in patients with congestive heart failure

A single-blind study of prenalterol 20-200 mg daily in a slow-release tablet preparation and a placebo was performed in 15 patients with moderate to severe congestive heart failure (NYHA II-IV) to evaluate the haemodynamic and clinical effects of oral prenalterol. Non-invasive parameters in the measurement of cardiac output, stroke volume, pre-ejection period index (PEPI), PEP/LVET ratio, ejection fraction and mean Vcf were significantly improved, indicating beneficial effects of prenalterol on cardiac contractility. Systolic blood pressure, heart rate and rate-pressure product were slightly increased at rest but were considerably lower during exercise. Arrhythmogenecity was not seen in the patients studied. Subjective improvement was noted in the majority of patients as evidenced by a decreased frequency of dyspnoea, fatigue and angina. Unwanted effects, such as palpitations and transmitted arm pulsations, were transient and disappeared with dose adjustment, while the inotropic effect of the medication was maintained. The clinical response appeared to be sustained for up to 2 weeks of treatment, indicating non-development of tachyphylaxis.

Metabolic effects of prenalterol in diabetic patients

In 16 non-diabetic and 16 diabetic patients prenalterol, dobutamine and dopamine infusions (5 micrograms/kg/min for 30 min) were given. The haemodynamic and metabolic changes were similar in diabetics and non-diabetics. Prenalterol has the most pronounced haemodynamic effect on heart rate (increase 25-47%) and the heart rate-blood pressure-product (increase 54-81%). The metabolic effects were moderate. The slight lipolytic effect of prenalterol documented its functional selectivity for beta 1-adrenoceptors.

Echocardiographic comparison between prenalterol and dobutamine

Prenalterol, a new cardioselective beta 1-adrenoceptor agonist, was compared with the beta-stimulator dobutamine by computer-assisted echocardiography. Prenalterol decreased preload, increased heart rate and induced an increase in contractility for a longer time in comparison with dobutamine. The small influence on blood pressure and afterload indicates selective beta 1-receptor-effect by a result of slight changes in the peripheral vascular resistance.

Effect of intravenous prenalterol on haemodynamics and myocardial lactate extraction in patients with left ventricular failure

To assess the immediate haemodynamic and myocardial metabolic effects of the beta 1-agonist prenalterol, we studied by cardiac catheterisation the response to 50 and 100 micrograms/kg given intravenously in 16 patients with congestive heart failure secondary to coronary artery disease or non-ischaemic cardiomyopathy. At peak effect, cardiac index increased from 2.6 +/- 0.5 to 3.2 +/- 0.8 1/min/m2 (mean +/- SD) p less than 0.001); peak rate of left ventricular pressure development rose from 963 +/- 242 to 1355 +/- 411 mm Hg per second (p less than 0.001); left ventricular end-diastolic pressure fell from 27 +/- 6 to 13 +/- 7 mm Hg (p less than 0.001); coronary sinus blood flow increased from 120 +/- 39 to 147 +/- 55 ml/min (p less than 0.01); myocardial oxygen consumption was augmented from 12.9 +/- 3.9 to 15.7 +/- 5.8 ml/min (p less than 0.001); and heart rate increased slightly (76 +/- 12 to 86 +/- 14 beats per minute, p less than 0.05). No significant changes occurred in left ventricular systolic pressure, stroke volume index, myocardial lactate extraction rate, myocardial arteriovenous oxygen difference and no patient developed angina, ECG-changes or ventricular arrhythmias. Infusion of prenalterol effectively improved the haemodynamic function and cardiac metabolism in congestive cardiomyopathy.

High-dose prenalterol in beta-blockade intoxication

This study presents a case of beta-blocker intoxication due to massive overdose of metoprolol (7.5 g). Prenalterol in a dose of 420 mg was given as antidote, in combination with epinephrine in intermittent doses. Resuscitation was performed during 4 hours because of mechanical asystole. The patient regained health in 24 hours after further repeated doses of 30 mg prenalterol. Prenalterol is valuable in the management of toxic doses of beta-blocking drugs, and a titration to extremely high doses of prenalterol might be necessary.

The haemodynamic effects of intravenous prenalterol and ouabain in conscious dogs

Experiments were performed on 5 resting conscious dogs supplied with an electromagnetic flow probe on the ascending aorta and a chronic aortic catheter for pressure recording. The animals were used repeatedly in four different types of experiment involving i.v. administration of 1. saline (controls), 2. prenalterol 45 nmol/kg (approximately 10 micrograms/kg) followed by an additional dose of 135 nmol/kg 20 min later, 3. ouabain 50 nmol/kg (approximately 30 micrograms/kg) and 4. a combination of protocols 2. and 3. Ouabain and the low dose of prenalterol exerted clear-cut positive inotropic effects as reflected in increased stroke volume and max dF/dt without significant changes in heart rate or arterial pressure. The PQ interval increased with ouabain but decreased with prenalterol. The higher dose of prenalterol caused a further rise in max dF/dt, a further shortening of the PQ time, increased heart rate and reduction in systemic vascular resistance. Higher doses of ouabain could not be given due to side-effects (vomiting). The combined treatment with ouabain and prenalterol showed their inotropic responses to be additive. Arrhythmias did not occur in any of the animals at the applied dose levels of the drugs. The experiments show that prenalterol through its beta 1-adrenoceptor stimulating action exerts a positive inotropic effect which surpasses that of emetic doses of ouabain. The inotropic response at moderate doses occurs without a change in heart rate. This fact and the apparent lack of influence of prenalterol on vascular alpha- and beta 2-adrenoceptors make the substance potentially useful clinically as an inotropic agent in cardiac failure, particularly in view of its relatively long duration of action.

The inhibitory GTP-binding protein (Gi) regulates the agonistic property of beta-adrenergic ligands in isolated rat adipocytes. Evidence for a priming effect of cyclic AMP

Prenalterol, an allegedly beta 1-selective adrenergic agonist with high intrinsic sympathomimetic activity (ISA), was shown to be weakly lipolytic in rat adipocytes. However, in pertussis-toxin-treated adipocytes, the ISA of prenalterol was markedly increased (from 10-20% to approx. 100% of that of isoprenaline). The cellular sensitivity was also increased (EC50 approx. 60 nM and approx. 3 microM in pertussis-toxin-treated and control cells respectively). A similar effect was seen for other partial agonists such as the beta 2-selective agonist terbutaline and for beta-adrenergic antagonists with some intrinsic activity (metoprolol, pindolol). There was no clear change in sensitivity to isoprenaline's ability to stimulate adenylate cyclase in adipocyte membranes from pertussis-toxin-treated animals but the cyclase activity was increased approx. 4-fold in the presence of 1 microM-GTP. Prenalterol stimulated lipolysis by only small increases in intracellular cyclic AMP (cAMP) levels (less than 10% of that seen with isoprenaline). Basal lipolysis was increased in cells from pertussis-toxin-treated rats and the cellular sensitivity to the non-degradable cAMP analogue, N6-monobutyryl-cAMP, was increased. In control cells, a submaximal concentration of prenalterol (0.1 microM) increased the sensitivity to the cAMP analogues, N6-monobutyryl-cAMP and 8-bromo-cAMP. A low concentration (1 mM) of 8-bromo-cAMP also increased the effect of prenalterol. Similar effects were seen when the phosphodiesterase was inhibited. Thus (1) lipolysis is extremely sensitive to small increases in intracellular cAMP; (2) the degree of activation of adenylate cyclase and thus cAMP formation is the rate-limiting step for the biological response of partial agonists; (3) the inhibitory GTP-binding protein, Gi, is an important modulator ('tissue factor') of the beta-adrenergic agonistic property; (4) low levels of cAMP exert a priming effect on protein kinase A.

Changes in coronary haemodynamics and myocardial metabolism at rest and during exercise after a cardiotonic drug (prenalterol) in patients with coronary artery disease

To elucidate the myocardial metabolic and haemodynamic effects of an inotropic drug in patients with coronary artery disease (CAD) without evident congestive heart failure (CHF), the acute effects of prenalterol were studied in nine patients. Patients with documented CAD by leftsided cardioangiography and end-diastolic pressure greater than 15 mm Hg were included in the study. They were examined at rest and during supine exercise at a level just below their anginal threshold before and after prenalterol. At rest, rate pressure product (RPP) increased by 40% (P less than 0.01), cardiac index rose 20% (P less than 0.01), cardiac venous flow (CVF) increased by 18% (P less than 0.05), and myocardial oxygen consumption (MVO2) increased by 20% (P less than 0.05) after prenalterol administration. Despite a decrease in mean pulmonary capillary venous pressure (PCV) of 40% (P less than 0.01), myocardial lactate extraction fell significantly (P less than 0.01) and lactate production was observed in three of nine patients compared to before prenalterol administration. During exercise, RPP increased by 20% (P less than 0.01), cardiac index remained unchanged, CVF increased by 25% (NS) and MVO2 showed a tendency to an increase (NS) after prenalterol administration. Mean PCV pressure decreased by 30% (P less than 0.01). Myocardial lactate extraction was markedly reduced during exercise (P less than 0.01) and five of nine patients showed lactate production compared to that before prenalterol administration. Thus, despite a decrease in left ventricular filling pressure, increased myocardial oxygen demand occurred after acute administration of prenalterol. Prenalterol and probably similar inotropic drugs should be used cautiously in patients with CAD without clinical evidence of congestive heart failure.

The immediate haemodynamic and electrophysiological response to prenalterol during fixed rate pacing in patients with chronic ischaemic heart disease

The immediate haemodynamic and electrophysiologic effects of intravenous prenalterol 2.5-75 micrograms/kg in patients with coronary heart disease without clinical heart failure were investigated during fixed rate atrial pacing. Right ventricular peak dP/dt increased pronounced and serum concentration dependent after prenalterol concomitant with an increase in stroke volume and a moderate decrease in peripheral vascular resistance. The effects on haemodynamics after prenalterol were thus serum concentration dependent but with marked interindividual variation. AV nodal conduction velocity increased significantly. It is concluded that prenalterol possess pronounced inotropic properties. The haemodynamic response to prenalterol intravenously is to a lesser degree dependent on the chronotropic effects of the drug and it is often unpredictable.

Arrhythmogenic dose of acetylstrophanthidin unchanged by beta-sympathomimetics in conscious dogs

The enhanced arrhythmogenic risk of combined treatment with cardiac glycosides and beta-sympathomimetics is referred in some textbooks, but only a few detailed studies on in vivo models are available. We therefore investigated this problem in conscious dogs in an intraindividual study. We determined the dose of acetylstrophanthidin (intravenous infusion of 5 mcg/kg per min), which provoked ventricular premature beats with and without concomitant treatment with the partial beta-agonistic compounds doxaminol (3 mg/kg p.o.), prenalterol (0.4 or 1.0 mg/kg p.o.) or isoprenaline (0.31 +/- 0.100 mcg/kg per min). In some dogs a coronary artery was narrowed in order to reduce the coronary blood supply. The arrhythmogenic dose of acetylstrophanthidin was nearly the same in all the groups investigated (range from 52.1 +/- 5.66 to 59.9 +/- 3.23 mcg/kg). Whereas the arrhythmogenic dose of acetylstrophanthidin was unchanged by beta-sympathomimetics, the combination of the glycoside and each of the beta-agonistic drugs increased the contractile force more than did either single compound. We therefore conclude that the arrhythmogenic risk of the combination of glycosides and beta-sympathomimetics may be--at least in experimental models--less than has been suggested in the past.

Apparent superiority of H2-receptor stimulation and simultaneous beta-blockade over conventional treatment with beta-sympathomimetic drugs in post-acute myocardial infarction: cardiac effects of impromidine--a new specific H2-receptor agonist-in the surviving catecholamine-insensitive myocardium

Left ventricular infarction (AMI) was produced in experimental animals and the contractile response to beta-adrenergic and H2-histaminergic stimulation by isoproterenol and impromidine tested in the isolated perfused heart preparation. Adenylate cyclase activity as well as binding characteristics of [3H]-dihydroalprenolol ([3H]-DHA), [3H]-methyl-tiotidine ([3H]-TIOT) and [3H]-quinuclidinyl benzilate ([3H]-QNB) to cardiac beta 1-, H2- and cholinergic muscarinic receptors were determined in sarcolemmal membrane preparations of the right ventricle of the same hearts. In addition, an attempt was made to elucidate the therapeutic value of post-AMI treatment with impromidine in the presence and absence of beta-blockade, in contrast to administration of prenalterol and the conventional therapy with beta-sympathomimetic drugs, e.g. dobutamine. Three days post-AMI the dose-response curve for isoproterenol of right ventricular dP/dtmax was significantly depressed, while the inotropic effect of impromidine was not impaired. Stimulation of adenylate cyclase activity by isoproterenol was reduced by 80% whereas impromidine and NaF stimulation rates were unaltered. Receptor-binding studies indicated a 90% loss and 10-times lowered affinity (KD) of the remaining beta-receptors while specific [3H]-TIOT- and [3H]-QNB-binding was unchanged. Administration of dobutamine increased mortality rates and extension of infarct size, led to a further decrease in contractile response to isoproterenol, induced complete insensitivity of adenylate cyclase to isoproterenol stimulation and caused pronounced additional reduction of number and affinity of [3H]-DHA-binding sites. In contrast, all above alterations were prevented by treatment with either prenalterol or combined administration of impromidine plus metoprolol. It is concluded, that these alterations in the non-ischemic, uninvolved myocardium post-AMI are the result of catecholamine-induced specific damage of sarcolemmal beta-receptors. Furthermore, treatment with H2-agonists in combination with beta-blocking agents may have beneficial effects, whereas conventional therapy with beta-sympathomimetic drugs tends to worsen the already depressed function of the beta-adrenergic stimulation mechanism.

Influence of heart rate on the effects of prenalterol on regional myocardial blood flow and function during coronary stenosis in dogs

The effects of prenalterol, a selective beta 1-adrenoceptor agonist with potent cardiac positive inotropic properties have been investigated on regional myocardial blood flow (RMBF) (microspheres) and contractile function (ultrasonic crystals) during partial circumflex coronary artery stenosis in 8 open-chest anaesthetized dogs. Prenalterol was investigated at two intravenous doses: 5 micrograms kg-1, which increased myocardial contractility (dP/dt max: +29%) more than heart rate (+12%, up to 150 beats min-1) and 20 micrograms kg-1 which induced almost similar increases in contractility (+35%) and heart rate (+31% up to 175 beats min-1). The induced modifications of regional flow and function were then compared to those produced in another series of 6 dogs by atrial pacing at 150 and 175 beats min-1 respectively. Prenalterol significantly increased RMBF and segment length (SL)-shortening in a dose-dependent manner in the nonischaemic zone. In the ischaemic zone, RMBF was maintained and SL-shortening increased with prenalterol, 5 micrograms kg-1 whereas both RMBF and contractile function were severely decreased with prenalterol, 20 micrograms kg-1. Atrial pacing had almost no effect on RMBF and SL-shortening in the nonischaemic zone. In the ischaemic zone, atrial pacing rate-dependently decreased both RMBF and SL-shortening. Thus, a significant increase in contractility, associated with little tachycardia (prenalterol, 5 micrograms kg-1), induces beneficial effects on RMBF and function in both the nonischaemic and ischaemic myocardium. In contrast, a strong tachycardia, whether accompanied by positive inotropic effects (prenalterol, 20 gig kg-') or not (atrial pacing at 175 beats min-1) induces deleterious effects on RMBF and cardiac function in the ischaemic myocardium.

Hemodynamic trial of sequential treatment with diuretic, vasodilator, and positive inotropic drugs in left ventricular failure following acute myocardial infarction

The circulatory effects induced by two sequential intravenous treatment programs with a diuretic, arteriolar or venodilator , and a positive inotropic drug were studied in a randomized between-group trial in 20 male patients with radiographic and hemodynamic evidence of left ventricular (LV) failure following acute myocardial infarction (AMI). Furosemide induced a substantial diuresis in both groups of patients, in association with reductions in LV filling pressure (p less than 0.01) and cardiac output (p less than 0.05), without significant change in heart rate or systemic arterial pressure. The addition of isosorbide dinitrate was followed by reductions in the systemic arterial (p less than 0.01) and LV filling pressures (p less than 0.01) without significant change in the heart rate or cardiac output. Hydralazine after furosemide reduced systemic vascular resistance (p less than 0.01), but the fall in mean blood pressure (p less than 0.01) was limited by the increase in cardiac output (p less than 0.01); heart rate was also increased (p less than 0.01) and LV filling pressure fell (p less than 0.05). The final addition of the beta-1 adrenoceptor agonist, prenalterol, increased systemic arterial systolic pressure (p less than 0.05), cardiac output (p less than 0.05), and heart rate (p less than 0.01), and reduced systemic vascular resistance (p less than 0.01) in both groups; these changes were greatest in those pretreated with furosemide and isosorbide dinitrate. In both treatment pathways compared with control the reductions in systemic vascular resistance and left heart filling pressure were accompanied by increases in heart rate and cardiac output without substantial changes in systemic blood pressure. Which of these hemodynamic pathways offers the optimum prognosis awaits further study.

Intravenous and oral prenalterol in congestive heart failure. Effects on systemic and coronary hemodynamics and myocardial catecholamine balance

Systemic and coronary hemodynamic effects of prenalterol, a beta-1 receptor agonist, were determined in patients with chronic congestive heart failure, initially after intravenous administration (10 patients) and then after oral administration (eight patients). Cardiac index increased by 33 percent and 30 percent after intravenous and oral prenalterol, respectively. The increase in stroke volume index and stroke work index and decrease in pulmonary capillary wedge pressure and systemic vascular resistance were not significant. Myocardial oxygen consumption and coronary sinus blood flow increased in the majority of patients, although these changes were not statistically significant. There were no significant changes in transmyocardial norepinephrine or epinephrine balance. The systemic and coronary hemodynamic effects of both intravenous and oral prenalterol were similar. Major side effects included sudden death (two patients) and hypotension and bradycardia (three patients) during oral prenalterol treatment. It is concluded that improved left ventricular function following both intravenous and oral prenalterol may be associated with increased myocardial oxygen consumption, and serious adverse effects may occur during prenalterol therapy.

Prenalterol in cardiogenic shock following acute myocardial infarction

Eleven patients with cardiogenic shock following acute myocardial infarction (AMI) have been treated with prenalterol. This drug was administered in seven patients once dobutamine or dopamine proved to be ineffective or poorly effective, and it was the first inotropic drug employed in four patients. Therapeutic dose of intravenous infusion ranged from 2.2 to 18 micrograms/kg/min (mean dose: 7 micrograms/kg/min), and was maintained for 2 to 4 hours. Since two patients received the infusion on two different occasions, a total of 13 cases were considered for statistical analysis. Prenalterol produced an increase in cardiac index (p less than 0.01), mean aortic pressure (p less than 0.02), net work index (p less than 0.01), net/stroke work index (p less than 0.01), pressure rate product (p less than 0.05), and myocardial perfusion gradient (p less than 0.02). It decreased systemic (p less than 0.02) and pulmonary (p less than 0.01) vascular resistances, pulmonary artery (p less than 0.01) and pulmonary capillary (p less than 0.05) pressures. Heart rate and right atrial pressure were not significantly changed. The drug acted as a relatively selective inotropic agent without a chronotropic effect and with minimal peripheral actions. It was effective in seven patients and ineffective in four patients. Thus prenalterol appears to be a useful drug in cardiogenic shock and further studies are warranted.

A method for simultaneous epicardial monophasic action potential recordings from the dog heart in situ

In order to record epicardial monophasic action potentials (MAP) simultaneously from different regions of intact beating hearts, we developed a tripodal suction electrode device (total weight 1.5 g, distance between the flexible silicone legs 25 mm) which we tested in pentobarbital anaesthetized open chest dogs. The device was easy to apply and gave stable and reproducible recordings. Repolarization times for epicardial left ventricular and endocardial right ventricular MAPs correlated well (r = 0.97, P less than 0.001). There was no correlation between MAP amplitude and repolarization times. The beta 1-adrenergic agonist prenalterol decreased MAP duration, while the new class III antiarrhythmic drug melperone increased MAP duration. Mild ischaemia effected MAP prolongation and severe ischaemia MAP shortening, compared to simultaneous recordings from non-ischaemic ventricular regions. We conclude that the new tripodal suction electrode is a simple device for simultaneous recording of multiple MAPs. The method should be suitable for studies of electrophysiological effects of drugs and other interventions in intact beating hearts.

Long-term hemodynamic effects of prenalterol in patients with severe congestive heart failure

In a controlled, randomized, double-blind study we investigated the long-term effects of the beta 1-adrenoceptor agonist prenalterol in 16 patients with severe congestive heart failure (NYHA class III or IV). Previous to and 1 week, 3 months, and 6 months after continuous oral intake of 40 to 120 mg prenalterol a day, catheterization of the right heart combined with an ergometer test was carried out; M mode and two dimensional echocardiograms as well as systolic time intervals were also recorded. With prenalterol the heart rate increased within 1 week from 81 +/- 7 to 90 +/- 7 beats/min (mean +/- SD) (p less than .05) and remained increased after 3 months (93 +/- 9 beats/min, p less than .01) and 6 months (91 +/- 6 beats/min, p less than .05). After 1 week the cardiac index rose from 2.7 +/- 0.7 to 3.3 +/- 0.7 l/min/m2 (p less than .01), and after 3 and 6 months it fell again to 3.0 +/- 0.9 l/min/m2 and 2.9 +/- 0.7 l/min/m2, respectively. In the ergometer test the improvement in performance was not significant. The mean velocity of circumferential fiber shortening initially increased from 0.58 +/- 0.20 to 0.79 +/- 0.28 circumferences/sec (p less than .01), but dropped after 3 months to 0.62 +/- 0.31 circumferences/sec. The ejection fraction determined from the two-dimensional echocardiogram rose after 1 week from 20 +/- 10 to 27 +/- 12% (p less than .05), but decreased again after 3 months (23 +/- 11%) and 6 months (20 +/- 10%).(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine versus dobutamine after open-heart surgery

The haemodynamic effects of dopamine and dobutamine were compared in a cross-over study of 12 patients in the early postoperative phase after open-heart surgery. The drug infusion rates (dopamine (microgram/kg/min) mean 6.5, range 2.8-12, dobutamine (microgram/kg/min) mean 7.9, range 4.3-12.3) were adjusted so that the cardiac output increased by 50%. With both drugs this was achieved through simultaneous increases in stroke volume (dopamine + 16%, dobutamine + 9%) and heart rate (dopamine + 31%, dobutamine + 38%). The systemic vascular resistance did not change with dopamine but decreased significantly (-18%) with dobutamine. Therefore, the systolic and diastolic arterial blood pressures rose significantly more with dopamine than with dobutamine. The left atrial pressure increased with dopamine but was unchanged with dobutamine. The urine output was significantly higher with dopamine than with dobutamine.

Haemodynamic effects of prenalterol in acute myocardial ischaemia in open chest pigs

The haemodynamic effects of prenalterol, a new sympathomimetic agent, have been studied in anaesthetized open-chest pigs with acute myocardial ischaemia provoked by left anterior descending coronary artery ligation. A group of eight animals was infused with saline and served as control (C). In both groups the ligation of the left anterior descending coronary artery determined a significant (P less than 0.05) reduction of aortic flow, maximum left ventricular (LV) dp/dt with no changes in heart rate. The infusion of a first dose of 30 micrograms/kg of prenalterol restored the depressed haemodynamics but increased significantly the heart rate in the prenalterol group while the saline infused group did not show any significant changes. The haemodynamic effects of prenalterol were still evident 25 min after the infusion. The subsequent administration of a second dose of 60 micrograms/kg of prenalterol resulted in a further improvement of the aortic flow, LV dp/dt and heart rate which reached values higher than in the basal condition. The positive inotropic effect was not associated with changes in stroke volume, therefore the increase in aortic flow was essentially due to an increase of the heart rate. It is concluded that prenalterol is a powerful inotropic agent in acutely infarcted animals. Its action on aortic flow appears to be related to an increase in heart rate in contrast to some previous observations.

Beta-adrenoceptor blocker intoxication: epidemiological data. Prenalterol as an alternative in the treatment of cardiac dysfunction

1 During the three years 1978--1980 the Swedish Poison Information Centre received reports of 184 patients hospitalized due to beta-adrenoceptor blocker overdosage. Of the 35 patients who developed signs of severe cardiac dysfunction (HR less than 50 beats/min, systolic blood pressure less than 80 mm Hg), 23 had ingested propranolol, 10 metoprolol and 2 alprenolol. 2 The mean value of the defined daily doses (DDD) per 1000 inhabitants per day in Sweden during these years were 11.97 for propranolol, 8.02 for alprenolol and 7.74 for metoprolol. The incidence of severe poisoning due to alprenolol overdosage is lower than expected according to DDD. 3 During 1979 19 persons died from overdosage with beta-adrenoceptor blockers in Sweden: 15 due to propranolol (non-selective, lacks intrinsic sympathomimetic activity), 2 to metoprolol (cardioselective, lacks intrinsic sympathomimetic activity). These findings indicate that severe and even fatal poisoning may occur regardless of the type of beta-blocking agent. 4 The usefulness of prenalterol, a cardioselective beta-adrenoceptor partial agonist, in reversing unwanted cardiac effects of beta-adrenoceptor blocking agents is illustrated by two cases of massive propranolol intoxication (maximal plasma concentrations of propranolol 7.2 and 7.8 mumol/l respectively). Prenalterol in high doses (130 and 280 mg/24 h respectively) restored cardiac function.

Effects of the beta-adrenergic receptor agonist pirbuterol on cardiac performance during acute ischaemic left ventricular failure in dogs

The effects of the beta-adrenergic receptor agonist pirbuterol on left ventricular (LV) performance were examined during acute ischaemic LV failure in anaesthetized dogs. Plastic microspheres (50 microns) were injected into the left main coronary artery, and the dogs developed severe LV failure. The stability of the heart failure model was demonstrated in a group of untreated control dogs (n = 5). Administration of pirbuterol 7 micrograms X kg-1 i.v. during failure caused an increase in cardiac output from 1.52 +/- 0.14 (mean +/- S.E.M., n = 7) to 2.56 +/- 0.32 1 X min-1 (P less than 0.01) at 30 min after drug administration. The LV end-diastolic pressure (LVEDP) decreased from 24.6 +/- 1.1 to 21.0 +/- 1.9 mmHg (P less than 0.05), and maximum LV dP/dt was increased from 2012 +/- 124 to 2602 +/- 119 mmHg X s-1 (P less than 0.01). The LVEDP-stroke work relation (n = 2) shifted markedly upward. Heart rate was not significantly changed by pirbuterol. Mean aortic blood pressure and total peripheral resistance decreased from 103 +/- 3 to 85 +/- 5 mmHg (P less than 0.05) and from 68 +/- 6 to 34 +/- 4 mmHg X 1(-1) X min (P less than 0.01), respectively. Pirbuterol increased plasma free fatty acid concentrations from 264 +/- 45 (n = 4) to a maximum value of 956 +/- 169 mumol X 1(-1). In conclusion, by a combination of inotropic stimulation and systemic vasodilation, pirbuterol markedly improved cardiac performance in dogs with acute ischaemic LV failure.

Effects of prenalterol on cardiac performance and transmural myocardial perfusion in patients with chronic renal failure

The acute haemodynamic effects of the beta-adrenoreceptor agonist, prenalterol, were studied in six patients with chronic end-stage renal failure. Prenalterol 0.8 mg, 1.6 mg, and 3.2 mg was administered i.v. as a bolus, and after the last dose the selective adrenergic beta-1-receptor antagonist metoprolol was administered i.v. in doses of 5 and 10 mg. The haemodynamic effects of the drugs were investigated using impedance cardiography and radionuclide angiocardiography. The main haemodynamic effects were a dose-related chronotropic effect, demonstrated by an increase in heart rate (26%; less than 0.05), and an inotropic effect, shown by an increase in stroke volume index (20%; p less than 0.05) and left ventricular ejection time (12%; p less than 0.05); the cardiac index was increased by 47% (p less than 0.05). Transmural myocardial perfusion (DPTI/SPTI ratio) was decreased by 22% (p less than 0.05) after prenalterol. It is concluded that prenalterol has positive inotropic and chronotropic effects in patients with chronic renal failure, that the improvement in left ventricular performance is at the expense of a decreased transmural myocardial perfusion, and that metoprolol is a specific antidote.

beta 1-and beta 2-adrenoceptor stimulatory effects of prenalterol

Prenalterol, previously characterized as a functionally cardioselective partial beta-adrenoceptor agonist, was shown to relax K+ -elicited contractures in the uterine muscle from progesterone pretreated rats (pD2 7.7) and to increase beating rate in the rat right atrium (pD2 8.0) at about the same concentrations with maximal effects corresponding to 94 and 82% respectively of those of isoproterenol. Terbutaline, with equal maximal effects as isoproterenol, was 50 times more potent in the uterus (pD2 7.8) than in the right atrium (pD2 6.1). Both tissues displayed a high sensitivity to isoproterenol (pD2 9.1 in both tissues) indicating large receptor reserves for the full agonist. The maximal relaxing effect of prenalterol in the uterus was obtained at about a three-fold increase of the cyclic AMP content, which is similar to that obtained with isoproterenol at a corresponding relaxation. The effects in the uterine muscle of all three agonists were mediated through beta 2-adrenoceptors since beta 2-adrenoceptor blockers (ICI 118, 551 and IPS 339) antagonized the effects in concentrations which had only marginal effects on the atrial responses of the agonists. The beta 1-antagonists pafenolol and pamatolol in concentrations higher than those, which blocked the effects of the agonists on beating rate, were devoid of inhibitory effects in the uterus. These results indicate that prenalterol possesses the ability to elicit a functional response by stimulation of either beta 1-or beta 2-adrenoceptors provided that the tissue has a large spare receptor reserve for full agonists.

Aspects of the pharmacology of beta-adrenoceptor agonists and antagonists

A short review is given of the distribution of and effects mediated through beta-receptors. The pharmacodynamic profiles of some beta-receptor agonists and antagonists are briefly outlined and the clinical advantages and disadvantages of different pharmacodynamic properties are discussed.

The haemodynamic effects of dopamine and prenalterol in patients after cardiac valve surgery

The haemodynamic effects of prenalterol and dopamine were compared in 10 patients about 4 h after cardiac valve replacement during a phase of temporarily depressed myocardial function. The rate of infusion was adjusted to give similar increases in stroke volume with the two drugs (dopamine + 17% and prenalterol + 18%). Both drugs produced marked inotropic and chronotropic effects with significant increases in heart rate, cardiac output, arterial blood pressure, and left and right ventricular stroke work. The arterial blood pressure and the left ventricular stroke work increased significantly more with dopamine than with prenalterol, however. The systemic vascular resistance decreased significantly with prenalterol, whereas it was unchanged with dopamine. The effects of prenalterol could be traced after 90 min, whereas the effects of dopamine vanished within 15 min.

New hope for the failing heart

One sixth of this nation's citizens have disease of the heart and blood vessels; an estimated 3.5 to 4 million Americans have chronic cardiac failure. The individual and collective losses associated with heart failure are enormous. Standard medical therapy with digitalis and diuretics is frequently inadequate to control and morbidity associated with this often times malignant process. More effective medical therapy is therefore needed. The recent development of potent, orally active cardiotonic agents may make this objective a reality. At the present time, the new cardiotonic agents are still in the experimental stages of investigation. Phase II and III clinical trials must be either initiated or completed before the efficacy and safety of these agents will be known. It must be emphasized that objective parameters of ventricular function and the patients's quality of life must be monitored if meaningful verdicts are to be rendered. Information must be gathered that indicates whether prolonged therapy with these agents is detrimental to the myocardium. Despite this caveat, the availability of compounds having potent inotropic properties had generated much anticipation and excitement in clinical cardiology. Our ability to more effectively manage patients with chronic cardiac failure may now be on the horizon. There is, indeed, new hope for the failing heart.

Cardiovascular effects of prenalterol on rest and exercise haemodynamics in patients with chronic congestive cardiac failure

?The cardiovascular effects of the cardioselective beta, agonist prenalterol have been studied in nine patients with severe chronic congestive cardiac failure and in six patients with left ventricular dysfunction resulting from previous myocardial infarction. In the patients with cardiac failure intravenous prenalterol in a dosage of 1.5 microgram/kg bodyweight increased the cardiac index from 1.8 +/- 0.1 to 21.+/- 0.1 1/min per m2 and the left ventricular ejection fraction from 22 +/- 3 to 28 +/- 3%. There was a modest but significant increase in heart rate from 76 +/- 3 to 87 +/- 4 beats/min. Systemic vascular resistance fell from 2285 +/- 51 to 2041 +/- 534 dynes s-1 cm-5. On exercise, the left ventricular filling pressure fell from 33 +/- 6 to 26 +/- 3 and both cardiac index and stroke index increased by 13% and 16%, respectively. There was no significant change in heart rate or systemic blood pressure. In the patients with left ventricular dysfunction, coronary sinus blood flow increased from 107 +/- 11 to 133 +/- 12 ml/min but the increase in myocardial oxygen consumption was small and not significant (11.6 +/- 1.2 and 14.5 +/- 1.9 ml/min). In all patients there was no evidence that prenalterol was arrhythmogenic.

Sympathomimetic amines: potential clinical applications in ischemic heart disease

Sympathomimetic amines are useful in the treatment of patients with ischemic heart disease complicated by heart failure and shock. These agents influence the cardiovascular system by action on alpha-adrenergic, beta-adrenergic, and dopamine receptors. Recent evidence has demonstrated the existence of subtypes of the classic adrenergic and dopamine receptors that mediate distinct physiologic effects. The relative actions of sympathomimetic amines on these receptors differ substantially, resulting in considerable variation in their cardiac and peripheral vascular effects. Two classes of sympathomimetic amines are being intensively investigated at present: (1) compounds acting predominantly on beta 1-adrenergic receptors (i.e., they increase cardiac contractile force with little or no peripheral vascular effects) and (2) compounds acting on both beta 1-adrenergic and dopamine receptors. Orally active compounds of these two classes have been synthesized recently and are now under study for the treatment of patients with heart failure. Results of preliminary studies with such components are briefly reviewed.

Cardiostimulatory effects of prenalterol, a beta-1 adrenoceptor partial agonist, in vivo and in vitro. Correlation between physiological effects and adenylate cyclase activity

The cardiostimulatory effects of prenalterol, a beta-1-adrenoceptor partial agonist, were studied in vivo and in vitro and compared to those evoked by isoprenaline, a full agonist, and to those of other partial agonists. In the anaesthetized rat, prenalterol and terbutaline were found not to elevate the myocardial cyclic AMP content; this was in sharp contrast to isoprenaline. Both partial agonists did, however, produce significant effects on heart rate. In the anaesthetized cat, prenalterol exhibited chronotropic and inotropic intrinsic activities of 88 and 76% respectively in relation to isoprenaline. No statistically significant increase in myocardial cyclic AMP content could however be detected. Prenalterol did not stimulate adenylate cyclase significantly in the cat myocardial homogenate. This was also true of the beta-2-adrenoceptor selective partial agonist procaterol. In this preparation, isoprenaline, noradrenaline and adrenaline acted as full agonists. Furthermore, prenalterol produced a concentration-dependent inhibition of isoprenaline-activated adenylate cyclase. Our data indicate that maximal cardiac stimulation occurs at a low level of adenylate cyclase activation and low myocardial cyclic AMP concentration when provoked by a full beta-adrenoceptor agonist. The maximal physiological effects of a partial agonist such as prenalterol may consequently be achieved at a marginal activation of the adenylate cyclase. The present data may thus support the hypothesis of a large beta-adrenoceptor reserve for full agonists in the heart.

Hemodynamic effects of atrial pacing and prenalterol infusion in patients taking beta-adrenergic blocking drugs

Prenalterol, a beta-adrenergic agonist, was given to nine patients with angiographically proved coronary artery disease. Subjects were studied during chronic beta-adrenergic blockade. The adequacy of blockade was assessed by the exercise heart rate response and by plasma concentrations of blocking agents. After incremental doses of 2.5 mg, 5.0 mg and 7.5 mg of prenalterol, heart rate was increased by 20%, 24% and 38%, respectively, and left ventricular dP/dt max by 55%, 73% and 61%, respectively. Systolic and diastolic blood pressures did not change significantly; pulmonary artery wedge pressure fell from 10 +/- 0.5 mm Hg to 7.1 +/- 0.9 and 6.7 +/- 0.7 mm Hg after 2.5 mg and 5.0 mg, respectively (p less than 0.01 for both). The net inotropic response to prenalterol was assessed, independent of the chronotropic response, using incremental atrial pacing before and after drug infusion. At identical heart rates, left ventricular dP/dt max increased by 40%, 49% and 48% after 2.5 mg, 5.0 mg and 7.5 mg, respectively. Left ventricular cineangiography before and after infusion showed an increase in ejection fraction from 0.73 +/- 0.02 to 0.83 +/- 0.03 (p less than 0.001). Plasma prenalterol concentration estimations demonstrated a clear, dose-related inotropic response, the level of response in each patient being largely determined by the degree of beta-adrenergic blockade at the time of the study.

Central and peripheral haemodynamic effects of prenalterol in patients with coronary heart disease

The acute haemodynamic effects of prenalterol, a selective adrenergic beta-I-receptor agonist were studied in eight patients with coronary heart disease. Prenalterol was administered intravenously in four increasing doses to a cumulative dose of 5.6 mg. Fifteen minutes after the last dose of prenalterol two doses of the selective adrenergic beta-I-receptor antagonist metoprolol were administered intravenously to a cumulative dose of 17-5 mg. Ten minutes after each dose cardiac output, heart rate, arterial blood pressure, pulmonary artery pressure, systolic time intervals and forearm blood flow were determined. Haemodynamic effects of prenalterol: cardiac index and heart rate increased maximally by 38% and 39% respectively. Stroke index was increased by 6-9% after the first and second dose. Mean blood pressure was increased by 9.8 mmHg. Total peripheral resistance index was reduced by 19%. The mean pulmonary artery pressure decreased by 3.8 mmHg and pulmonary resistance index was reduced by 48%. Systolic time intervals were all reduced significantly after the second dose, which reflected the positive inotropic effects of prenalterol. Forearm blood flow increased by 29% and forearm vascular resistance was decreased by 20%. Haemodynamic effects of metoprolol: the haemodynamic changes induced by prenalterol were stepwise counteracted by metoprolol. After the second dose all the haemodynamic variables had returned to the control levels. It is concluded that prenalterol possesses a considerable positive inotropic as well as positive chronotropic effect on the myocardium. Both the chronotropic and inotropic effect of prenalterol was counteracted by metoprolol.

The effects of intravenous prenalterol on ventricular performance, as assessed by radionuclide ventriculography, in patients with ischaemic heart disease

1 We have observed the effects of intravenous prenalterol (1 mg and 2 mg) on ventricular performance, assessed by radionuclide ventriculography, in nine patients with ischaemic heart disease with varying degrees of impairment of ventricular performance. In seven of these patients the effects of prenalterol were compared with those of isoprenaline infused at 1 microgram/min. 2 Prenalterol caused no significant increase in heart rate, but systolic blood pressure increased by 26% (P less than 0.002). In contrast, isoprenaline caused heart rate to increase by 22% (P less than 0.02) and diastolic blood pressure to fall by 9% (P less than 0.01). 3 Left ventricular ejection fraction (LVEF) increased with both drugs, but the increase was greater with isoprenaline, as was the fall in the ratio mean ejection time: left ventricular ejection time, which is an index of improved ventricular performance. 4 Because of the increased heart rate and stroke volume produced by isoprenaline, cardiac output increased 45% above control values (P less than 0.001), but the increase in cardiac output after prenalterol did not reach statistical significance. 5 In three patients with very poor ventricular function (LVEF less than 0.30) prenalterol had little effect on ejection fraction, and caused increased regional ventricular dyskinesia. 6 The increase in systolic blood pressure, and therefore cardiac afterload brought about by prenalterol may limit ventricular response. The response might be enhanced by the addition of vasodilator therapy.

Clinical results with prenalterol in patients with heart failure

The hemodynamic effect of 75 to 225 microgram/kg prenalterol (PNL) intravenously were studied at rest and during exercise in eight patients with chronic congestive heart failure (CHF) after myocardial infraction (three patients), valvular surgery (three patients), and congestive cardiomyopathy (two patients). All head New York Health Association functional class III and IV CHF and were receiving digitalis and diuretics. With PNL at rest, left ventricular filling pressure (LVFP) fell from 17 to 12 mm Hg, cardiac index (CI) rose from 2.1 to 2.9 L/min/m2, heart rate (HR) increased mildly, systemic vascular resistance (SVR) declined moderately, and peripheral arterial pressure was unchanged. During PNL exercise compared with control, LVFP rise was less and CI, HR, and SVR responses were similar; dyspnea and angina were reduced in most patients. The eight patients were than given PNL orally, 30 to 200 mg/day, versus placebo for 6 days with comparative evaluation by echocardiogram, systolic time intervals (STI), exercise test, and continuous ECG. With PNL orally five of eight patients improved symptomatically, ejection fraction increased from 0.44 to 0.53, and STI preejection period shortened by 10 msec, without change in resting HR or systemic arterial blood pressure. The incidence of ventricular premature beats was not increased. PNL orally vs placebo exercise capacity increased 10%. Thus PNL may be of value for long-term CHF treatment in addition to conventional therapy.

Short- and long-term effects of hydralazine and combined hydralazine-prenalterol therapy in severe chronic congestive heart failure

The hemodynamic benefits of combined administration of prenalterol (P) with hydralazine (H) were evaluated in ten patients with severe chronic heart failure. Single administration of 100 mg H increased cardiac index (CI) from 2.3 to 3.0 l/min/m2, whereas pulmonary capillary wedge pressure (PWC) remained unchanged. After 3--4 weeks of treatment with 200 mg H hemodynamic improvementt was maintained (CI: 2.9 l/min/m2). Additional administration of P caused further augmentation of CI (3.3 l/min/m2). After long-term treatment with the combination of H and P sustained augmentation of CI (3.2 l/min/m2), and, furthermore, a slight but significant decrease of PCW were observed (p less than 0.05 vs. chronic single H-therapy). Five patients were able to perform exercise testing; H improved maximal exercise capacity and exercise hemodynamics in three patients. Further improvemen was observed after combined treatment (H + P) in three of five patients. It is concluded, the prenalterol may enhance the effectiveness of hydralazine therapy in congestive heart failure by providing concomitantly the principal actions of the vasodilator and positive inotropic agent used separately. Furthermore, the results indicate that oral long-term administration of hydralazine and prenalterol can produce sustained beneficial improvement.

Hemodynamic effects of intravenous prenalterol in severe heart failure

Nine patients with chronic severe low output heart failure (radionuclide left ventricular ejection fraction 17 +/- 5 percent [mean +/- standard deviation], left ventricular filling pressure 26 +/- 6 mm Hg, cardiac index 1.9 +/- 0.4 liters/min per m2, left ventricular stroke work index 18 +/- 6 g-m/m2) from various causes were treated with intravenous prenalterol (a new catecholamine-like inotropic agent) in doses of 1,4 and 8 mg. Significant hemodynamic improvement occurred as measured by increased left ventricular ejection fraction (to 26 +/- 4 percent), decreased left ventricular filling pressure (to 21 +/- 8 mm Hg) and increased cardiac index (to 2.4 +/- 0.6 liters/min per m2) and left ventricular stroke work index (to 25 +/- 8 g-m/m2). Significant increases in heart rate (from 87 +/- 18 to 91 +/- 18 beats/min) and mean systemic arterial pressure (from 87 +/- 8 to 92 +/- 7 mm Hg) also occurred. Peak hemodynamic response occurred at various doses. Significant adverse effects associated with prenalterol consisted of increased ventricular ectopic beats in two patients and asymptomatic ventricular tachycardia in two patients. Thus, intravenous prenalterol produces hemodynamic improvement in patients with a chronic severe low output state but may be associated with increased ventricular ectopic activity.

Immediate haemodynamic effects of prenalterol, a new adrenergic beta-1-receptor agonist, in healthy volunteers

The acute haemodynamic effects of prenalterol, a selective adrenergic beta-1-receptor agonist, were studied in eight healthy male volunteers. Prenalterol was administered i.v. in five increasing doses to a cumulative dose of 5.55 mg. After the last dose of prenalterol, three doses of the selective adrenergic beta-1-receptor antagonist metoprolol were administered i.v. to a cumulative dose of 17.5 mg. After each dose, cardiac output (CO), stroke volume (SV), blood pressure (BP), heart rate (HR), systolic time intervals (STI) and forearm blood flow (FBF) were determined. Prenalterol had the following effects: CO was significantly increased by 21.0% after the fourth dose, but the fifth dose did not further change CO. SV was unchanged after the first four doses, but after the fifth dose a significant decrease in SV of 7.0% was seen. Mean BP was increased significantly by 7.7%, but diastolic BP remained unchanged. HR was increased by 28.4%. Total peripheral resistance was reduced by 8.8%. STI were reduced significantly after the second dose, which indicates that prenalterol has a positive inotropic action. FBF was increased significantly after the fourth dose. After the third dose of metoprolol, the CO, SV, means BP, HR, STI and FBF had returned to their control values. It is concluded that prenalterol has positive inotropic and chronotropic effects on the myocardium, and that metoprolol is a specific antidote.