Direct vasodilator and positive inotropic actions of amrinone

Myocardial phosphodiesterases and regulation of cardiac contractility in health and cardiac disease

Phosphodiesterase (PDE) inhibitors are potent cardiotonic agents used for parenteral inotropic support in heart failure. Contractile effects of these agents are mediated through cAMP-protein kinase A-induced stimulation of I (Ca2+) which ultimately results in increased Ca(2+)-induced sarcoplasmic reticulum Ca(2+) release. A number of additional effects such as increases in sarcoplasmic reticulum Ca(2+) stores, stimulation of reverse mode Na(+)-Ca(2+) exchange, direct or cAMP-mediated effects on sarcoplasmic reticulum ryanodine receptor, stimulation of the voltage-sensitive sarcoplasmic reticulum Ca(2+) release mechanism, as well as A(1) adenosine receptor blockade could contribute to positive inotropic responses to PDE inhibitors. Moreover, some PDE inhibitors exhibit Ca(2+) sensitizer properties as they could increase the affinity of troponin C Ca(2+)-binding sites as well as reduce Ca(2+) threshold for thin myofilament sliding and facilitate cross-bridge cycling. Inotropic responses to PDE inhibitors are significantly reduced in cardiac disease, an effect largely attributed to downregulation of cAMP-mediated signalling due to sustained sympathetic activation. Four PDE isoenzymes (PDE1, PDE2, PDE3 and PDE4) are present in myocardial tissue of various mammalian species, of which PDE3 and PDE4 are particularly involved in regulation of cardiac myocyte contraction. PDE cAMP-hydrolysing activity is preserved in compensated cardiac hypertrophy but significantly reduced in animal models of heart failure. However, clinical studies have not revealed any changes in distribution profile as well as kinetic and regulatory properties of myocardial PDEs in failing human hearts. A reduction of PDE inhibitors-induced contractile responses in heart failure has therefore been ascribed to reduced cAMP synthesis due to uncoupling of adenylyl cyclase from beta-adrenoreceptor. In cardiac myocytes, PDEs are targeted to distinct subcellular compartments by scaffolding proteins such as myomegalin, mAKAP and beta-arrestins. Over subcellular microdomains, cAMP hydrolysis by PDE3 and PDE4 allows to control the activity of local pools of protein kinase A and therefore the extent of protein kinase A-mediated phosphorylation of cellular proteins.

Reevaluating the role of phosphodiesterase inhibitors in the treatment of cardiovascular disease

First developed for clinical use in the late 1980s, the phosphodiesterase inhibitors were found to increase the levels of the ubiquitous second messenger cyclic adenosine monophosphate and could effect changes in vascular tone, cardiac function, and other cellular events. After several early studies using high doses of phosphodiesterase inhibitors in patients with severe heart failure suggested adverse consequences, they fell out of favor. However, recent investigations of phosphodiesterase inhibitors in patients with intermittent claudication have demonstrated profound benefits. Furthermore, these agents have proven useful in prevention of cerebral infarction and coronary restenosis, and their use in the treatment of heart failure is being reevaluated. The reemergence of phosphodiesterase inhibitors can be attributed to a better understanding of dosing and drug-specific pharmacology, the use of concomitant medications, and a recognition of unique ancillary properties; however, their use still requires caution.

Electrophysiological effects of amrinone on the automaticity and membrane current system of the rabbit sinoatrial node cells

To elucidate the physiological role of phosphodiesterase (PDE) in cardiac pacemaker cells, we studied the electrophysiological effects of amrinone, an inhibitor of PDE type III, on the spontaneous action potential (AP) and membrane currents, using small preparations (0.2 x 0.2 x 0.1 mm) of rabbit sinoatrial (SA) node cells. Amrinone (0.1-1.0 mM) progressively increased the AP amplitude, maximal rate of depolarization, and spontaneous firing frequency, shortened the AP duration, and made the threshold potential more negative. In voltage-clamp experiments using double microelectrode techniques, 0.1 mM amrinone increased the Ca2+ current (I(Ca)) obtained on step depolarization from -40 to -10 mV by 25.86% +/-4.6% (P < 0.05, n = 6), the delayed rectifier K+ current (I(K)) tail obtained on repolarization from 10 to -60 mV by 22.8%+/-4.7% (P < 0.05, n = 6), and the hyperpolarization-activated inward current (Ih) at -90 mV by 19.5%+/-7.3% (P < 0.05, n = 6), respectively. Amrinone did not affect the slope factors of either the inactivation curve for I(Ca) (finfinity curve) or the activation curve for the delayed rectifier I(K) (pinfinity curve). These results suggest that this PDE III inhibitor exerts a positive chronotropic action by enhancing the availability and the conductance of all the tested membrane currents in rabbit SA node cells.

Differential effects of phosphodiesterase inhibitors on accumulation of cyclic AMP in isolated ventricular cardiomyocytes

The intracellular actions of phosphodiesterase (PDE) inhibitors on the accumulation of cyclic nucleotides were studied in isolated ventricular cardiomyocytes from adult Sprague-Dawley rats. Elevated levels of cyclic AMP, due to the effects of selective PDE inhibitors, were detected only when the levels of cyclic nucleotide were enhanced with forskolin (10 microM). The time course for the elevation of cyclic AMP levels was similar for all the PDE inhibitors tested, following the pattern of an initial rise in the first 2-4 min, proceeded by a steady state at 67 +/- 6% of the maximum stimulation. HN-10200 (2-[3-methoxy-5-methylsulfinyl-2-thienyl]-1H-imidazo-[4,5-c]- pyridine hydrochloride), a new imidazopyridine derivative, had a similar concentration-dependent profile to the structurally related compound, sulmazole (AR-L 115 BS, 2-[2-methoxy-4-methylsulfinyl)phenyl]-1H- imidazo-[4,5-b]-pyridine). Both the non-selective inhibitor, 3-isobutyl-1-methylxanthine (IBMX), and the selective PDE IV inhibitor, Ro 20-1724 (4-[(3-butoxy-4-methoxyphenyl)methyl]-2- imidazolidinone), potentiated the forskolin-stimulated levels of cyclic AMP with a much greater efficacy than sulmazole or HN-10200. The concentrations of forskolin required by IBMX, sulmazole and HN-10200 (10(-3) M) to increase levels of cyclic AMP by 4 pmol/mg protein were 3.2 x 10(-6) M, 1.32 x 10(-5) M and 1.46 x 10(-5) M, respectively. Enoximone failed to cause an increase in the levels of cyclic AMP, even when stimulated with maximal concentrations of forskolin. Furthermore, in the presence of forskolin, enoximone attenuated the response of Ro 20-1724 and IBMX in a concentration-dependent manner. Enoximone, similarly to HN-10200, sulmazole, Ro 20-1724 and IBMX did not produce any significant effect on levels of cyclic GMP under elevated conditions in the presence of sodium nitroprusside. The combined action of Ro 20-1724, with either HN-10200, sulmazole, or IBMX (10(-4) M), on intracellular levels of cyclic AMP, was not greater than the response to Ro 20-1724 alone. These data demonstrate the differential actions of PDE III and PDE IV inhibitors in rat ventricular cardiomyocytes. It is suggested that enoximone has a high selectivity for the PDE III isoenzyme so that hydrolysis of cyclic AMP by the PDE IV isoenzyme is not inhibited, in accordance with the lack of increase in cyclic AMP by enoximone in rat cardiomyocytes. HN-10200 and sulmazole, producing small increases in intracellular levels of cyclic AMP, are less selective PDE III inhibitors than enoximone.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute positive inotropic intervention: the phosphodiesterase inhibitors

Phosphodiesterase inhibitors that are selective for cAMP-specific cardiac and vascular PDE III comprise a new group of agents for the treatment of heart failure, which at present are limited to clinical shortterm intravenous use and research uses only. Although both intravenous amrinone and milrinone are FDA approved, only amrinone is available for general clinical use. Selective phosphodiesterase inhibition produces beneficial actions of positive inotropy and peripheral vasodilation that result from increased cardiac and vascular muscle concentrations of intracellular cAMP and ionic calcium. In addition, a positive lusitropic action (enhancement of cardiac relaxation) has been observed. Neither beta-adrenergic agonist activity nor inhibition of the sodium-potassium ATPase is produced by these agents. The magnitude of hemodynamic improvement generally exceeds that of the cardiac glycosides and is comparable with that of intravenous catecholamines such as dobutamine. The different pharmacodynamic profile of the PDE inhibitors is additive to the effects of cardiac glycosides, complementary and synergistic to the actions of catecholamines, and has been shown to have favorable effects on coronary hemodynamics. As a result there is continued enthusiasm for the short-term intravenous use of amrinone and potentially milrinone in the setting of acute heart failure resulting from systolic dysfunction (after myocardial infarction, open heart surgery, or infectious or toxic myocarditis), heart failure resulting from right ventricular systolic dysfunction, and when patients with severe heart failure await cardiac transplantation. Initiation of treatment with an intravenous bolus followed by a maintenance infusion provides prompt increases in stroke volume and cardiac output and simultaneous reductions in right and left ventricular filling pressures and systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactive effects of isoflurane and amrinone in the feline intestinal and renal circulation

Interactive effects of the phosphodiesterase-III inhibitor amrinone and isoflurane were investigated in cats. Cardiac output (thermodilution method), and intestinal (IBF) and renal (RBF) blood flows (optical flowmetry) were measured. Intestinal (IVR) and renal (RVR) vascular resistances were derived. To discriminate between pressure-related local myogenic vascular responses and primary vascular drug effects, intestinal and renal perfusion pressures (50 mmHg; 6.7 kPa) were controlled. The protocol included steady-state recordings with and without isoflurane in a randomized order, both before and after the administration of amrinone (2 mg.kg-1 i.v. + 2 mg.kg-1.h-1 i.v.. Amrinone induced no significant changes in IVR or RVR during basal chloralose anesthesia. During administration of 0.8% isoflurane, amrinone produced decreases in IVR and RVR, which were more pronounced than the vasodilator responses induced by this dose of isoflurane alone. On the other hand, with 1.6% isoflurane, amrinone did not add to the vasodilation. The cardiac effects of isoflurane and amrinone were small. Our data indicate that the vascular tone before administration of amrinone could be crucial for the vascular response of the drug and that isoflurane can significantly influence the regional circulatory effects of amrinone.

Pressure-volume analysis as a method for quantifying simultaneous drug (amrinone) effects on arterial load and contractile state in vivo

Pressure-volume relation analysis was used to independently quantify changes in ventricular contractile performance and vascular loading in intact anesthetized dogs before and after a single bolus of intravenous amrinone. Ventricular systolic property changes were characterized by the end-systolic elastance (Ees = slope of the end-systolic pressure-volume relation) and arterial properties by the effective arterial elastance (Ea = end-systolic pressure/stroke volume ratio). Pressure-volume data were obtained by the conductance catheter technique with loading varied by transient inferior vena cava occlusion. Amrinone induced a 27% increase in ejection fraction at 10 min (from 44% to 56%) as a result of both a significant rise in contractility (mean Ees 4 +/- 2 to 6 +/- 3 mm Hg/ml, p less than 0.001) and simultaneous reduction in arterial loading (Ea reduction from 6 +/- 2 mm Hg/ml to 5 mm Hg/ml, p less than 0.001). Over the subsequent 30 min, Ea revealed a significant recovery toward baseline, whereas Ees was less altered. Mean percent changes (% delta) in both variables were linearly correlated: % delta Ea = -1.6 x % delta Ees + 3.1, r = 0.96, p less than 0.001. In addition to separating ventricular from vascular property changes, the pressure-volume coupling framework was used to predict net pump performance (ejection fraction). Model predictions showed good agreement with experimental data. Thus, pressure-volume relations can be used to separately quantitate simultaneous changes in ventricular and vascular loading properties in vivo produced by pharmacologic agents with complex actions. Use of this approach in drug testing in humans should simplify data interpretation regarding mechanisms of action in specific clinical settings.

Inotropic mechanisms of amrinone in papillary muscles from guinea-pig hearts

Isometric force and action potentials were recorded in papillary muscles from guinea-pigs (temperature 33 degrees C, stimulation frequency 0.5 Hz). Amrinone (1 mM) increased peak twitch force (to 220% of control, n = 12) and rate of rise of force (to 221% of control, n = 12), while time from peak to half-relaxation was markedly reduced (to 70% of control). The time to peak force was not significantly changed. Action potential at 50% repolarization was shortened (93.3% of control, n = 8), whereas plateau voltage became more positive. Peak twitch force in response to a test stimulus after a varied interval, i.e. mechanical restitution, was increased at all intervals by the drug. However, the time to full mechanical restitution (1.5 s) was not affected. Forces in response to the test interval preceding the previous contraction (post-extrasystolic potentiation) were analysed. Maximum potentiation was 16.0 mN mm-2 (2.7 +/- 0.4%) before and 22.6 mN mm-2 (1.7 +/- 0.1%) after addition of the drug, i.e., the relative potentiation was diminished in the presence of the drug. The test interval for optimum potentiation was shortened from 370 to 320 ms (P less than 0.05, n = 12) in 1 mM amrinone. During decay of post-extrasystolic potentiation peak force of the post-potentiated contraction was linearly related to force of the potentiated contraction. The slope of this line (which is believed to monitor recirculation of activator calcium) was increased by amrinone from 0.37 to 0.50 (P less than 0.01, n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of amrinone and dobutamine on hemodynamics and myocardial oxygen balance in dogs with experimental left ventricular failure

The purpose of the present study was to induce left ventricular failure in anesthetized dogs by repeated ventricular fibrillation and then to determine if amrinone is effective in circulatory support by comparing the effects of amrinone and dobutamine. After the repetitive ventricular fibrillation, mean arterial pressure and stroke volume index decreased, pulmonary capillary wedge pressure (PCWP) increased, and acute left ventricular failure occurred. Thereafter, dogs were divided into the following four groups. In Group C (n = 6), normal saline was administered; in Group D (n = 6), dobutamine was administered at 7 micrograms/kg/min; and in Groups A40 (n = 6) and A80 (n = 7), amrinone was administered at 40 micrograms/kg/min and 80 micrograms/kg/min, respectively. Stroke volume index increased by 78% in Group D and 46% in both Groups A40 and A80. Pulmonary capillary wedge pressure decreased by 44% in Group A40 and 38% in Group A80, but remained unchanged in Group D. Similarly, total peripheral resistance decreased by 32% in Group A40, 29% in Group A80, but remained unchanged in Group D. These results suggest that amrinone increased cardiac output and decreased both preload and afterload. In the coronary circulation, both drugs caused direct coronary vasodilation since they increased myocardial oxygen supply in excess of the increase in myocardial oxygen demand. Neither drug produced signs of myocardial ischemia, as indicated by myocardial lactate metabolism. Amrinone should be a useful drug after open heart surgery, especially in cases where significant adverse effects of catecholamines occur or where a low-output state with increased preload and afterload exists.

Milrinone enhances cytosolic calcium transient and contraction in rat cardiac myocytes during beta-adrenergic stimulation

We have investigated the mechanism that underlies the absence of a positive inotropic effect of milrinone on rat myocardium. The twitch characteristics of enzymatically dissociated left ventricular myocytes from the adult rat and guinea pig were assessed by edge tracking during field stimulation. In some rat myocytes loaded with the ester derivative of the Ca2+ probe Indo-1 we simultaneously measured changes in cell length and in the associated cytosolic Ca2+ (Cai) transient. Our results show that in guinea pig myocytes bathed in 0.5 mM [Ca2+] and field stimulated at 1 Hz, milrinone (10 microM) had a positive inotropic effect. In contrast milrinone had no effect on the contractile properties of rat myocytes studied under similar conditions and field stimulated at 0.2 Hz. In rat myocytes bathed in 0.5 mM [Ca2+] and stimulated at 0.2 Hz isoproterenol (1 nM) increased the amplitude and shortened the duration of the contraction and of the associated Cai transient; these effects of beta-adrenergic stimulation were further enhanced by the addition of milrinone (10 microM) in the presence of isoproterenol. Under conditions of higher cell Ca2+ loading achieved by raising bathing [Ca2+] to 1 mM and isoproterenol to 3 nM the positive inotropic effect of milrinone (10 microM) in rat myocytes saturated when spontaneous oscillatory Ca2+ release appeared in the diastolic intervals between electrically stimulated twitches. Our results suggest that an enhancement in the baseline beta-adrenergic stimulation is required for milrinone to exercise a positive inotropic action on rat myocardial tissue.

Tissue distribution and selective inhibition of subtypes of high affinity cAMP phosphodiesterase

High affinity cAMP phosphodiesterase (PDE), also referred to as PDE III, or low Km PDE occurs as two subtypes. One subtype is sensitive to inhibition by cGMP while the other is relatively insensitive. To be consistent with previously recommended nomenclature, these subtypes were designated Types IV and V PDEs respectively. Tissue distribution of these subtypes of high affinity cAMP PDE was investigated using comparative potencies of specific inhibitors. Of the tissues examined, dog heart contained the highest proportion of the cGMP inhibitable form (Type IV PDE), whereas dog kidney cortex and brain were composed almost entirely of the cGMP non-inhibitable form (Type V PDE). Enoximone and other new cardiotonic drugs that inhibit high affinity cAMP PDE were shown to be specific for the cGMP inhibitable form, whereas rolipram was specific for the cGMP non-inhibitable form. The apparently partially competitive kinetics shown by one of these drugs, enoximone, was due to the presence of both subtypes of the enzyme. When the activity of the cGMP non-inhibitable form was suppressed by rolipram, competitive inhibition of the cGMP inhibitable subtype by enoximone was observed. Rat heart high affinity cAMP PDE activity contained a higher proportion of the cGMP non-inhibitable subtype than did the enzyme from dog heart. It is suggested that this may account for the relative insensitivity of rats to the cardiotonic PDE inhibitors.

Effects of amrinone and dopamine on uterine blood flow and vascular responses in the gravid baboon

Amrinone is a bipyridine derivative with positive inotropic and vasodilator properties. We investigated its effects on uterine and iliac artery blood flow, blood pressure, and heart rate in 10 acutely instrumented gravid baboons. Amrinone was compared with dopamine, infused systemically or regionally via the common iliac artery. When given intravenously at a constant rate of 40 micrograms/kg/min, amrinone produced a slight increase in iliac artery blood flow but did not significantly alter mean arterial pressure, heart rate, or uterine artery blood flow. Dopamine at an intravenous dose of 40 micrograms/kg/min produced a mean (+/- SD) 49.2% +/- 18.7% increase in mean arterial pressure (p less than 0.01) and a 84.2% +/- 56.1% increase in uterine vascular resistance (p less than 0.01), but caused no changes in heart rate, uterine artery blood flow, or iliac artery blood flow. Regional infusion of amrinone at the rate of 25 micrograms/kg/min produced a significant increase in iliac artery blood flow (p less than 0.01) without changing uterine artery blood flow, heart rate, or mean arterial pressure. Regional infusion of dopamine at concentrations of 2.5 to 25 micrograms/kg/min produced decreases in flow (p less than 0.01) and increases in resistance (p less than 0.01) in the uterine and iliac vascular beds. We conclude that amrinone dilates the vascular bed of the external iliac artery, but has no remarkable effect on the uterine vascular bed. Dopamine increases uterine vascular resistance and may impair uteroplacental perfusion.

The response of isolated guinea-pig aorta to amrinone

1. In helically cut strips of aorta from reserpine-treated guinea-pigs, cumulative concentrations (30 microM, 0.3 mM and 3 mM) of amrinone progressively reduced the basal tone of the preparations and relaxed the smooth muscle contracted by 1 microM noradrenaline or by 20 mM K+. 2. The relaxing effect was completely suppressed by tissue pretreatment with adenosine deaminase (1 U ml-1). 3. Relaxation induced by amrinone was not affected by 50 microM indomethacin or by 0.1 mM 8-phenyltheophylline and was potentiated by 5 microM quinidine. 4. Like amrinone, exogenous adenosine reduced the basal tone of the guinea-pig aorta strips and relaxed the preparations contracted by 1 microM noradrenaline or by 20 mM k+ in a concentration-dependent manner. 5. The relaxing activity of exogenous adenosine was not affected by 50 microM indomethacin, was potentiated by 5 microM quinidine and was partially antagonized by 0.1 mM 8-phenyltheophylline. 6. These results indicate the involvement of endogenous adenosine in the relaxing effect of amrinone on guinea-pig aorta strips, but the specific mechanism of amrinone-adenosine interaction remains to be elucidated.

[Hemodynamic effects of intravenous perfusion of amrinone in increasing doses in 12 patients with severe heart decompensation]

Twelve patients with severe heart failure were given amrinone by intravenous infusion in doses rising from 1 to 2, 3 and 4 mg X min-1, the interval between each dose being 30 min. The total cumulative dose was 300 mg over 120 min. Haemodynamic measurements were started the day before treatment to take into account nycthemeral fluctuations in haemodynamics and the possible effects of maintenance treatments and meals, all factors which might influence the baseline values. When given at a rate of more than 2 mg X min-1, amrinone significantly improved cardiac function (p less than 0.001). The mean pulmonary capillary pressure fell from 24.1 +/- 5.3 to 13.7 +/- 8.6 mmHg, and the cardiac index rose from 1.75 +/- 0.40 to 2.51 +/- 0.32 1 X min-1 X m-2. Heart rate and blood pressure were not significantly modified. No adverse reaction was observed during the infusion and the following 24 hours. Thus, intravenous amrinone proved effective in patients with severe heart failure, with maximal effects being obtained in doses of 3 mg X min-1.

Additive positive inotropic effects of milrinone, ouabain and calcium in diseased human ventricular myocardium

The interactions of milrinone, ouabain and calcium on force of contraction in isolated, contracting human papillary muscle strips were measured. Milrinone (EC50, 8 X 10(-5)M) increased force of contraction maximally by 2.8 +/- 0.8 mN at 5 X 10(-4)M; significantly less than either ouabain (1 X 10(-7)M; 4.8 +/- 0.5 mN increase) or calcium (15 mM; 6.2 +/- 0.6 mN increase). A submaximal, but not a maximal, inotropic effect of ouabain could be increased by the addition of milrinone; in contrast, both ouabain and calcium increased the maximal inotropic effect of milrinone by 1.7 +/- 0.2 mN and 2.7 +/- 0.3 mN, respectively. The combined inotropic effect of milrinone with either ouabain of 4.2 +/- 0.3 mN or calcium of 5.6 +/- 0.4 mN was not different from that with calcium or ouabain alone. We conclude that further positive inotropic effects should be expected when digitalis is given to patients with congestive heart failure who are already optimally treated with milrinone.

Role of reflex sympathetic withdrawal in the hemodynamic response to an increased inotropic state in patients with severe heart failure

Newer positive inotropic agents used in the treatment of severe heart failure not only increase cardiac contractility, but also cause peripheral vasodilation. It is not known to what extent this vasodilation is due to a direct peripheral action of the drug, as opposed to reflex withdrawal of sympathetic tone secondary to an augmented inotropic state. In 16 patients with severe heart failure, a 48 hour intravenous infusion of milrinone, a positive inotropic vasodilator drug, resulted in an increase in stroke volume index from 26 +/- 2 to 34 +/- 3 ml/m2 (p less than 0.001), a reduction in forearm vascular resistance measured by venous plethysmography from 43 +/- 5 to 27 +/- 3 U (p less than 0.003) and an increase in forearm venous capacitance from 2.1 +/- 0.2 to 2.9 +/- 0.2 ml/100 ml (p less than 0.001). To determine whether a withdrawal of sympathetic tone contributed to this vasodilation, milrinone was infused directly into the left main coronary artery in eight of the patients, thereby eliminating any direct vascular effects of the drug. Intracoronary milrinone (50 micrograms/min) caused an increase in peak positive first derivative of pressure (658 +/- 49 to 784 +/- 68 mm Hg/s; p less than 0.01) and stroke volume index (20 +/- 2 to 25 +/- 3 ml/m2; p less than 0.0001), which was associated with a reduction in plasma norepinephrine from 540 +/- 101 to 423 +/- 90 pg/ml (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of amrinone on right ventricular function: predominance of afterload reduction

Although the bipyridine agent amrinone is reported to have a positive inotropic effect on the left ventricle, the effect of this drug on right ventricular contractility in the clinical setting is unknown. We studied the effect of short-term intravenous administration of amrinone on right ventricular systolic function in nine patients with severe congestive heart failure and, using radionuclide ventriculography, examined the right ventricular end-systolic pressure-volume relationship to determine whether reduced right ventricular afterload or increased contractility predominantly accounted for the observed improvement in right ventricular systolic function. In each patient the right ventricular end-systolic pressure-volume relationship was derived with use of varying doses of nitroprusside. After nitroprusside was stopped, intravenous amrinone (3 mg/kg) caused decreases from baseline in pulmonary arterial end-systolic pressure in eight of nine patients (23 +/- 11% [overall mean +/- SE], p less than .05), and in pulmonary vascular resistance in all patients (38 +/- 6%, p less than .001). Right ventricular end-systolic volume decreased (23 +/- 8%, p less than .01) and right ventricular ejection fraction increased (31 +/- 10%, p = .01). The amrinone-induced decrease in right ventricular end-systolic volume was compared with that predicted for right ventricular afterload reduction alone based on the effect of amrinone on pulmonary arterial end-systolic pressure and the pressure-volume relationship observed during infusion of nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial pharmacodynamics of dopamine, dobutamine, amrinone and isoprenaline compared in the isolated rabbit heart

The isolated spontaneously beating rabbit heart was used for comparing the myocardial effects of isoprenaline, dobutamine, dopamine and amrinone. Both isoprenaline and dobutamine produced a progressive concentration-dependent increase in contractility from 100% to a maximum of about 200% (pD2 7.81 and 7.01, respectively) as measured by the increase in isotonic contraction rate. The simultaneous augmentations in contraction amplitude reached maxima of about 127 and 143% (pD2 7.83 and 7.05) for each of the drugs and the heart frequency rose to 202 and 162% (pD2 7.80 and 6.63), respectively. The accompanying oxygen consumption increased from 100 to 194% (pD2 7.70) for isoprenaline and to only 177% (pD2 6.36) for dobutamine. Coronary flow rate rose to 153 and 134%, respectively. Dopamine increased the contraction rate to 181% (pD2 6.26), contraction amplitude to about 122% (pD2 6.25) and heart rate to 162% (pD2, 5.85), while oxygen consumption rose to a maximum of 202% (pD2 5.69). Coronary flow rate rose to 156%. In contrast amrinone produced an unexpected slowly progressing decrease in contraction rate and contraction amplitude to about 66% (pD2 4.45 and 4.01, respectively). Oxygen consumption increased to 159% (pD2 4.10) and coronary flow rate to 210%. The positive inotropic effect of dobutamine thus equalled that of isoprenaline but with a distinct lower concomitant increase in heart frequency and oxygen consumption which may reflect a better myocardial efficiency during the action of dobutamine.

Relative contribution of inotropic and vasodilator effects to amrinone-induced hemodynamic improvement in congestive heart failure

The relative contribution of inotropic and vasodilator effect to amrinone-induced hemodynamic improvement in congestive heart failure (CHF) is unknown. In 9 patients with CHF, the effects of amrinone and nitroprusside on hemodynamic and radionuclide measurements were compared to determine whether reduced afterload accounts for the amrinone-induced decrease in left ventricular end-systolic volume. In each patient, the end-systolic pressure-volume relation was derived using nitroprusside. After terminating nitroprusside treatment, intravenous amrinone (3 mg/kg) caused end-systolic volume to decrease from 148 +/- 32 ml/m2 (mean +/- standard deviation) to 133 +/- 32 ml/m2 (p less than 0.05), causing an increase in cardiac index from 1.9 +/- 0.8 to 2.7 +/- 0.8 liters/min/m2 (p less than 0.001). Arterial end-systolic pressure decreased in all patients during amrinone administration, from 96 +/- 22 to 84 +/- 19 mm Hg (p less than 0.005), as did systemic vascular resistance. Nitroprusside doses needed to match the decrease in LV end-systolic volume induced by amrinone caused significantly greater decreases in arterial end-systolic pressure than did amrinone (p less than 0.01). The amrinone-induced decrease in end-systolic volume exceeded that predicted for a pure vasodilator based on arterial end-systolic pressure and the nitroprusside-derived pressure-volume relation in 6 patients. In 3 patients, the decrease in end-systolic volume did not exceed that expected for a pure vasodilator. In conclusion, after amrinone treatment, afterload reduction occurs in all patients with severe CHF and is the sole effect in some.(ABSTRACT TRUNCATED AT 250 WORDS)

Separation of the direct myocardial and vasodilator actions of milrinone administered by an intracoronary infusion technique

To determine the relative contributions of milrinone's positive inotropic and vasodilator actions in patients with severe congestive heart failure, the drug was administered by constant infusion directly into the left main coronary artery of 11 patients with New York Heart Association functional class III or IV heart failure. Intracoronary infusion of milrinone at rates up to 50 micrograms/min had no effect on mean arterial pressure or systemic vascular resistance but resulted in dose-related increases in peak positive dP/dt (+21%), stroke volume index (+18%), and stroke work index (+21%) and decreases in heart rate (-3%), mean right atrial pressure (-25%), and left ventricular end-diastolic pressure (-17%). In eight patients, intravenous administration (75 micrograms/kg) after the intracoronary infusion resulted in significant decreases in mean arterial pressure (-14%) and systemic vascular resistance (-40%), further increase in stroke volume index compared with intracoronary administration, and further decreases in mean right atrial and left ventricular end-diastolic pressures compared with intracoronary administration. These data indicate that milrinone exerts both positive inotropic and vasodilator actions that contribute significantly to the drug's overall hemodynamic effect.

Amrinone in the management of low cardiac output after open heart surgery

Hemodynamic effects of amrinone were studied in 2 groups of patients after open heart surgery. Group I consisted of 10 patients with moderate heart failure. In the absence of inotropic agents, their mean cardiac index (CI) was 2.02 +/- 0.41 liters/min/m2 and mean pulmonary capillary wedge pressure (PCWP) 19 +/- 3 mm Hg. Amrinone was administered 24 hours postoperatively by bolus injection (2 mg/kg) and by 12-hour infusions (20 micrograms/kg/min). Hemodynamic data and plasma concentrations were obtained 10 and 20 minutes after the bolus injection and at 1, 4, 8 and 12 hours during infusion. Significant beneficial changes were noted in CI, PCWP, right atrial pressure, systemic vascular resistance and pulmonary vascular resistance. Group II consisted of 5 patients in severe cardiogenic shock (mean CI 1.97 +/- 0.3 liters/min/m2, mean PCWP 28 +/- 8 mm Hg) despite adrenergic agonists in all patients and intraaortic counterpulsation in 2. After these measures, amrinone was given intravenously for 36 to 72 hours as additional inotropic support. Significant improvement was observed in CI, PCWP, right atrial pressure, systemic vascular resistance and pulmonary vascular resistance. Four patients in this group were discharged; 1 patient died after 5 days in acute renal failure and coma grade IV. No serious adverse effects of amrinone were observed in any group II patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intracoronary and intravenous amrinone infusions in patients with cardiac failure and patients with near normal cardiac function

The effects of intracoronary and intravenous infusions of amrinone were studied to distinguish the drug's direct cardiac actions from its peripheral vascular and neuroendocrine properties. Intracoronary infusions of amrinone were found to have no haemodynamic effect other than producing a slight reduction in the left ventricular ejection fraction and some suggestion of coronary vasodilatation in patients with impaired left ventricular function. They did not improve contractility, cardiac output, or filling pressures and had no significant effect on myocardial metabolism, although therapeutic concentrations of the drug were detected in coronary sinus blood. Intravenously administered amrinone reduced filling pressures and improved the cardiac index in all patients, but haemodynamic improvements were most pronounced in the patients with the worst cardiac function. These changes were accompanied by improvements in the indices of contractility only in patients in whom alterations in concentrations of free fatty acid, glycerol, and glucose suggested peripheral catecholamine release. In the patients with the best basal cardiac function intravenously administered amrinone produced a reduction in myocardial work and evidence of myocardial ischaemia, as a result of excessive reduction of coronary perfusion pressure and increased heart rate, without any appreciable increase in cardiac index. It is concluded that, at the concentrations of the drug that can be achieved in man without adverse effects, amrinone has no direct positive inotropic effect. Haemodynamic changes are predominantly the result of vasodilatation, although catecholamines may be released in some patients.

Positive inotropic and vasodilator actions of milrinone in patients with severe congestive heart failure. Dose-response relationships and comparison to nitroprusside

Milrinone is a potent positive inotropic and vascular smooth muscle-relaxing agent in vitro, and therefore, it is not known to what extent each of these actions contributes to the drug's hemodynamic effects in patients with heart failure. In 11 patients with New York Heart Association class III or IV congestive heart failure, incremental intravenous doses of milrinone were administered to determine the dose-response relationships for heart rate, systemic vascular resistance, and inotropic state, the latter measured by peak positive left ventricular derivative of pressure with respect to time (dP/dt). To clarify further the role of a positive inotropic action, the relative effects of milrinone and nitroprusside on left ventricular stroke work and dP/dt were compared in each patient at doses matched to cause equivalent reductions in mean arterial pressure or systemic vascular resistance, indices of left ventricular afterload. Milrinone caused heart rate, stroke volume, and dP/dt to increase, and systemic vascular resistance to decrease in a concentration-related manner. At the two lowest milrinone doses resulting in serum concentrations of 63 +/- 4 and 156 +/- 5 ng/ml, respectively, milrinone caused significant increases in stroke volume and dP/dt, but no changes in systemic vascular resistance or heart rate. At the maximum milrinone dose administered (mean serum concentration, 427 +/- 11 ng/ml), heart rate increased from 92 +/- 4 to 99 +/- 4 bpm (P less than 0.01), mean aortic pressure fell from 82 +/- 3 to 71 +/- 3 mmHg (P less than 0.01), right atrial pressure fell from 15 +/- 2 to 7 +/- 1 mmHg (P less than 0.005), left ventricular end-diastolic pressure fell from 26 +/- 3 to 18 +/- 3 (P less than 0.005), stroke volume index increased from 20 +/- 2 to 30 +/- 2 ml/m2 (P less than 0.005), stroke work index increased from 14 +/- 2 to 21 +/- 2 g X m/m2 (P less than 0.01), and dP/dt increased from 858 +/- 54 to 1,130 +/- 108 mmHg/s (P less than 0.005). When compared with nitroprusside for a matched reduction in mean aortic pressure or systemic vascular resistance, milrinone caused a significantly greater increase in stroke work index at the same or lower left ventricular end-diastolic pressure. Milrinone caused a concentration-related increase in dP/dt (32% increase at maximum milrinone dose), whereas nitroprusside had no effect. These data in patients with severe heart failure indicate that in addition to a vasodilating effect, milrinone exerts a concentration-related positive inotropic action that contributes significantly to the drug's overall hemodynamic effects. The positive inotropic action occurs at drug levels that do not exert significant chronotropic or vasodilator effects.

New positive inotropic drugs for the treatment of congestive heart failure

Positive inotropic agents can stimulate the severely depressed myocardium in late stages of heart failure. However, symptomatic benefits are only gained by improvement in the deranged peripheral circulation, which produces symptoms and limitations. In augmenting cardiac output and reducing filling pressures, the effects of positive inotropic agents and vasodilators are similar and additive, and the "contractile reserve of the heart" in response to inotropic stimulation may limit efficacy of these agents. Although symptomatic benefits occur in patients with severe heart failure after improvement in peripheral blood flow distribution, survival may not be altered, because this appears to be determined more by the amount of myocardial damage and its progression, and neither of these is affected by either inotropic agents or vasodilators. Indeed, in early stages of heart failure, therapy must be redirected toward preventing further myocardial cell loss rather than stimulating pump function.

Assessment of the inotropic and vasodilator effects of amrinone versus isoproterenol

The hemodynamic effects of graded-dose infusions of amrinone (maximal dose 30 micrograms/kg/min) (10 patients) and isoproterenol (maximum dose 4 micrograms/min) (11 patients) were assessed in patients with a range of left ventricular (LV) function. LV ejection fraction ranged from 0.13 to 0.77 (mean +/- standard deviation 0.47 +/- 0.23) among the patients who received amrinone and from 0.24 to 0.77 (mean 0.52 +/- 0.18) among those who received isoproterenol. Peak-dose amrinone produced a reduction in LV filling pressure (from 15 +/- 10 to 10 +/- 7 mm Hg, p less than 0.001), but no significant change in heart rate, cardiac output, mean aortic pressure, total systemic vascular resistance (TSVR) or LV dP/dt max. In contrast, peak-dose isoproterenol produced a similar reduction in LV filling pressure (from 17 +/- 12 to 13 +/- 13 mm Hg, p less than 0.05), but also caused increases in heart rate, cardiac output and LV dP/dt max and decreases in mean aortic pressure and TSVR (p less than 0.001). The absolute change in cardiac output and stroke volume correlated closely with the change in TSVR in response to amrinone (r = -0.90, p less than 0.001 and r = -0.84, p = 0.002, respectively), but not in response to isoproterenol. Although isoproterenol produced a marked increase in cardiac output and LV dP/dt max (not explained by heart rate changes alone) in all patients, amrinone produced an increase in cardiac output only in those with markedly elevated LV filling pressures (who had a reduction in TSVR), and an increase in LV dP/dt in a minority.

Hemodynamic and clinical limitations of long-term inotropic therapy with amrinone in patients with severe chronic heart failure

To determine the hemodynamic and clinical effects of long-term positive inotropic stimulation on the myocardium, we treated 31 patients with severe chronic heart failure with oral amrinone (600 mg daily) and performed invasive hemodynamic studies during short- and long-term treatment with the drug. Stroke volume and stroke work indexes increased markedly during the first 48 hr of therapy (p less than .01) but returned to pretreatment values after 2 to 10 weeks; upon drug withdrawal, both variables deteriorated rapidly to values significantly lower than those observed before treatment with amrinone (p less than .01), despite similar values for left ventricular filling pressure, mean arterial pressure, and systemic vascular resistance. This pattern of response indicated that progression of the underlying heart disease had occurred during treatment with amrinone and contributed importantly to its failure to produce long-term benefits. Progression of left ventricular dysfunction was associated with a progressive increase in heart rate and plasma renin activity and a decline in serum sodium concentration. Clinically, amrinone therapy was complicated by sustained symptomatic ventricular tachycardia in four patients, worsening myocardial ischemia in four patients, and worsening congestive heart failure in eight patients, all of whom had been stable before entry into the study; only three of the 31 patients improved clinically. Ten patients died during the first 2 weeks of treatment, and 16 (52%) were dead within 3 months, a mortality rate twice as great as that seen during comparable trials with vasodilating drugs. Although noncardiac adverse effects were frequent, they were not the primary reason for drug failure. In conclusion, long-term therapy with amrinone may accelerate progression of left ventricular dysfunction, exacerbate myocardial ischemia, and provoke life-threatening ventricular tachyarrhythmias, thereby shortening survival in patients with severe chronic heart failure. Prolonged administration of inotropic drugs may achieve short-term gains at the expense of long-term detrimental effects on the myocardium.

Echocardiographic evaluation of cardiovascular effects of amrinone

Amrinone, a new inotropic drug, was infused at a dosage of 2.5 mg/kg body weight in 14 patients affected by dilatative cardiomyopathy in New York Heart Association (NYHA) functional class III and IV. Cardiac index, mean arterial pressure, and some echocardiographic parameters were evaluated. Cardiac index (CI) increased from 2.03 +/- 0.24 to 2.82 +/- 0.43 1/min/m2 (p less than 0.001). Fractional shortening (FS) increased from 16.4 +/- 5.2 to 21.5 +/- 5.3% (p less than 0.05). End-diastolic and end-systolic diameters showed a significant reduction. Mean arterial pressure decreased from 90.7 +/- 88 to 87.3 +/- 8.4 mmHg (p less than 0.001), the end-systolic stress (ESS) decreased from 5.8 +/- 1 to 5.2 +/- 1 g/cm (p less than 0.001). Analyzing the relationship between FS and ESS, it was possible in some cases to suppose the presence of an important vasodilator effect of the drug. The afterload in 7 patients was therefore modified before and after infusion of the drug to analyze FS at the same levels of afterload. This was done to evaluate the vasodilator effect of amrinone. Examining the regression line of FS/ESS ratio it was possible to observe a predominant vasodilator effect in some patients, but in most, a sinergic action was noted. This may be useful for chronic treatment of congestive heart failure, reducing amrinone doses, and using it in association with other vasodilator drugs.

Oral amrinone for the treatment of chronic congestive heart failure: results of a multicenter randomized double-blind and placebo-controlled withdrawal study

A placebo-controlled study was employed to evaluate the effects of oral amrinone in patients with congestive heart failure. After a baseline period of at least 4 weeks of standard treatment for refractory congestive heart failure, oral amrinone was added to the treatment regimen of 173 patients. Patients were predominantly male (89%), aged 24 to 76 years (mean 54), with ischemic (52%) or idiopathic (37%) dilated cardiomyopathy, in New York Heart Association functional class II (40%), III (59%) and IV (1%) and having a mean (+/- standard deviation) left ventricular ejection fraction of 25 +/- 15%. Phase 1: After the addition of amrinone (113 +/- 33 mg three times daily), 52 patients (30%) showed a maximal increase in treadmill exercise time exceeding 2 minutes (Naughton protocol), 72 (42%) had a lesser increase, 24 (14%) developed limiting adverse reactions, 20 (12%) died and 5 dropped out of the study. Fifty-two "responders" (30%) who were free of limiting side effects and had a greater than 2 minute increase in exercise time were randomized in double-blind fashion to continued amrinone or switched to placebo (each plus standard treatment) for an additional 12 weeks. Phase 2: Comparison of 31 of these 52 responders who continued to receive amrinone with the remaining 21 randomized to placebo revealed no significant differences in vital signs, indexes of left ventricular size and function, systolic time intervals or maximal exercise time. Continued follow-up study of patients receiving either amrinone or placebo revealed decreases in exercise times of 7 and 10%, respectively (both p less than 0.05 compared with before randomization). Episodes of worsened congestive heart failure severe enough to mandate termination of double-blind treatment were as frequent in patients taking placebo (4[18%] of 21) as in those taking amrinone (4[13%] of 31; p = NS). The average symptom score and functional class of each treatment group remained comparable. Adverse effects such as gastrointestinal and central nervous system complaints were more common with amrinone treatment as were elevations of serum liver enzymes and reduced platelet counts. This large multicenter, randomized double-blind withdrawal study revealed no change in estimates of cardiac performance after the discontinuation of amrinone. These findings suggest that amrinone, in the dosages tested, does not importantly improve cardiac function beyond that provided by standard treatment with digoxin, diuretic drugs and vasodilators.

Non-additive positive inotropic effects of amrinone and ouabain on cat papillary muscles

Amrinone has been shown to produce haemodynamic benefits in digitalis-treated patients. Since amrinone is a positive inotropic agent on isolated heart muscle, these benefits may mean that amrinone increases the maximal ouabain-induced increase in force of contraction, without causing toxicity. We have therefore measured, in cat right ventricular papillary muscles, the inotropic effects of ouabain, amrinone alone and amrinone with a maximally effective, non-toxic ouabain concentration (2 X 10(-7) M). Ouabain is much more potent than amrinone (EC50-values: ouabain, 8 X 10(-8) M, amrinone, 1-2.8 X 10(-3) M). The highest amrinone concentration used (6 X 10(-3) M) produced a significantly lower increase in force of contraction than ouabain (2 X 10(-7) M) in the same muscles. After ouabain (2 X 10(-7) M) produced a stable effect, no further increase in force of contraction was observed with any amrinone concentration. Sustained arrhythmias were observed in five of six muscles at 3 X 10(-3) M amrinone with ouabain (2 X 10(-7) M), but in only one of these muscles with amrinone 3 X 10(-3) M alone. Since the positive inotropic effects of amrinone are not additive with those from a maximally effective ouabain concentration, the haemodynamic benefits seen in patients are probably due to non-cardiac effects of amrinone such as vasodilatation.

Hemodynamic and regional blood flow distribution responses to dextran, hydralazine, isoproterenol and amrinone during experimental cardiac tamponade

Four different interventions were examined in dogs with cardiac tamponade. Infusion of 216 to 288 ml saline solution into the pericardium reduced cardiac output from 3.5 +/- 0.3 to 1.7 +/- 0.2 liters/min as systemic vascular resistance increased from 4,110 +/- 281 to 6,370 +/- 424 dynes . s . cm-5. Left ventricular epicardial and endocardial blood flows were 178 +/- 13 and 220 +/- 12 ml/min per 100 g, respectively, and decreased to 72 +/- 14 and 78 +/- 11 ml/min per 100 g with tamponade. Reductions of 25 to 65% occurred in visceral and brain blood flows and in a composite brain sample. Cardiac output during tamponade was significantly increased by isoproterenol, 0.5 microgram/kg per min intravenously; hydralazine, 40 mg intravenously; dextran infusion or combined hydralazine and dextran, but not by amrinone. Total systemic vascular resistance was reduced by all interventions. Left ventricular epicardial flow was increased by isoproterenol, hydralazine and the hydralazine-dextran combination. Endocardial flow was increased by amrinone and the combination of hydralazine and dextran. Right ventricular myocardial blood flow increased with all interventions except dextran. Kidney cortical and composite brain blood flows were increased by both dextran alone and by the hydralazine-dextran combinations. Blood flow to small intestine was increased by all interventions as was that to large intestine by all except amrinone and hydralazine. Liver blood flow response was variable. The most pronounced hemodynamic and tissue perfusion improvements during cardiac tamponade were effected by combined vasodilation-blood volume expansion with a hydralazine-dextran combination. Isoproterenol had as dramatic an effect but it was short-lived. Amrinone was the least effective intervention.

Amrinone relaxing effect on the isolated guinea pig trachea and its interaction with aminophylline

The relaxing effect of Amrinone, an inotropic and vasodilating agent, was investigated on the isolated guinea pig tracheal smooth muscle in comparison and in association with Aminophylline. Amrinone (pD2 = 5.02 +/- 0.07) resulted more active than Aminophylline (pD2 = 4.25 +/- 0.08) in relaxing the isolated guinea pig trachea. The interaction curves of the two drugs showed the pattern typical for "competitive synergism", thus suggesting that Amrinone may act on tracheal muscle through inhibition of phosphodiesterase.

Amrinone activates K+-depolarized atrial and ventricular myocardium of guinea pigs

Amrinone is a new synthetic drug that increases contractile strength of mammalian heart muscle; however, its mechanism of positive inotropic action has not been determined. We now report that amrinone (0.053-5.3 mM) consistently restores typical slow response electromechanical activity fo K+-depolarized atrial and ventricular myocardial preparations from guniea pigs. This action was blocked in both tissues by D-600 (1 microM), but it was not significantly inhibited by either tetrodotoxin (23.5 microM), d,l-propranolol (1 microM), or phentolamine (10 microM). Cimetidine (3 microM) or metiamide (10 microM) slightly inhibited amrinone's effect only in the ventricle, whereas pyrilamine (10 microM) slightly inhibited amrinone's response only in the atrium. These data indicate that amrinone's positive inotropic action may involve augmented Ca++ influx via the slow inward Ca++ current, and that although this action is independent of adrenoceptor mechanisms, it seems to include a small histaminergic component.