Positive inotropic agents

Inodilators in septic shock: should these be used?

Septic shock involves a complex interaction between abnormal vasodilation, relative and/or absolute hypovolemia, myocardial dysfunction, and altered blood flow distribution to the tissues. Fluid administration, vasopressor support and inotropes, represent fundamental pieces of quantitative resuscitation protocols directed to assist the restoration of impaired tissue perfusion during septic shock. Indeed, current recommendations on sepsis management include the use of inotropes in the case of myocardial dysfunction, as suggested by a low cardiac output, increased filling pressures, or persisting signals of tissue hypoperfusion despite an adequate correction of intravascular volume and mean arterial pressure by fluid administration and vasopressor support. Evidence supporting the use of inotropes in sepsis and septic shock is mainly based on physiological studies. Most of them suggest a beneficial effect of inotropes on macro hemodynamics especially when sepsis coexists with myocardial dysfunction; others, however, have demonstrated variable results on regional splanchnic circulation, while others suggest favorable effects on microvascular distribution independently of its impact on cardiac output. Conversely, impact of inodilators on clinical outcomes in this context has been more controversial. Use of dobutamine has not been consistently related with more favorable clinical results, while systematic administration of levosimendan in sepsis do not prevent the development of multiorgan dysfunction, even in patients with evidence of myocardial dysfunction. Nevertheless, a recent metanalysis of clinical studies suggests that cardiovascular support regimens based on inodilators in sepsis and septic shock could provide some beneficial effect on mortality, while other one corroborated such effect on mortality specially in patients with proved lower cardiac output. Thus, using or not inotropes during sepsis and septic shock remains as controversy matter that deserves more research efforts.

Tolerance development as a pharmacological and clinical problem

Two main forms of acquired pharmacological tolerance may be distinguished, dispositional (pharmacokinetic) and pharmacodynamic. Pharmacodynamic tolerance is common, and can in many cases be attributed to adaptive receptor changes. Such changes of beta-adrenoceptors have been extensively studied and widely used as models for explaining the mechanisms of tolerance development. The mechanisms behind tolerance to adrenoceptor agonists are discussed, and also tolerance development to these and some other agents when used in the treatment of asthma, uterine hyperactivity and congestive heart failure.

Acute heart failure: inotropic agents and their clinical uses

Inotropic agents are indispensable for the improvement of cardiac contractile dysfunction in acute or decompensated heart failure. Clinically available agents, including sympathomimetic amines (dopamine, dobutamine, noradrenaline) and selective phosphodiesterase-3 inhibitors (amrinone, milrinone, olprinone and enoximone) act via cAMP/protein kinase A (PKA)-mediated facilitation of intracellular Ca2+ mobilisation. Phosphodiesterase-3 inhibitors also have a vasodilatory action, which plays a role in improving haemodynamic parameters in certain patients, and are termed inodilators. The available inotropic agents suffer from risks of Ca2+ overload leading to arrhythmias, myocardial cell injury and ultimately, cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and cellular metabolism. Furthermore, they lose their effectiveness under pathophysiological conditions, such as acidosis, stunned myocardium and heart failure. Pimobendan and levosimendan (that act by a combination of an increase in Ca2+ sensitivity and phosphodiesterase-3 inhibition) appear to be more beneficial among existing agents. Novel Ca2+ sensitisers that are under basic research warrant clinical trials to replace available inotropic agents.

Dual regulation of myofilament Ca2+ sensitivity by levosimendan in normal and acidotic conditions in aequorin-loaded canine ventricular myocardium

Experiments were carried out in canine ventricular trabeculae loaded with aequorin to investigate the effects of levosimendan {(R)-([4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]-hydrazono)-propanedinitrile} on contractile force and Ca(2+) transients in normal and acidotic conditions. The concentration-response curve for the positive inotropic effect (PIE) of levosimendan was bell-shaped, that is, it declined markedly at 10(-4) M after achieving the maximum at 10(-5) M in normal (pH(o)=7.4) and acidotic conditions (pH(o)=6.6). The positive inotropic effect (PIE) of levosimendan up to 10(-5) M was associated with an increase in Ca(2+) transients and a shift of the relationship of Ca(2+) transients and force to the left of that of elevation of [Ca(2+)](o). Levosimendan at 10(-4) M elicited a negative inotropic effect (NIE) in association with a further increase in Ca(2+) transients, and during washout Ca(2+) transients increased further, while the force was abolished before both signals recovered to the control. In acidotic conditions, the relationship of Ca(2+) transients and force during the application of levosimendan in normal conditions was essentially unaltered, whereas the PIE was suppressed due to attenuation of the increase in Ca(2+) transients. In summary, in intact canine ventricular myocardium, levosimendan elicits a dual inotropic effect: at lower concentrations, it induces a PIE by a combination of increases in Ca(2+) transients and Ca(2+) sensitivity, while at higher concentrations it elicits an NIE due to a decrease in Ca(2+) sensitivity. Acidosis inhibits the PIE of levosimendan due to suppression of the increase in Ca(2+) transients in response to the compound.

The therapeutic potential of novel cardiotonic agents

During the course of treatment of heart failure patients, cardiotonic agents are inevitable for improvement of myocardial dysfunction. Clinically available agents, such as beta-adrenoceptor agonists and selective phosphodiesterase 3 inhibitors, act mainly via cyclic AMP/protein kinase A-mediated facilitation of Ca(2+) mobilisation (upstream mechanism). These agents are associated with the risk of Ca(2+) overload leading to arrhythmias, myocardial cell injury and premature cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and metabolic effects. Cardiac glycosides act also via an upstream mechanism and readily elicit Ca(2+) overload with a narrow safety margin. No currently available agents act primarily via an increase in the myofilament sensitivity to Ca(2+) ions (central and/or downstream mechanisms). Novel Ca(2+) sensitisers under basic research may deserve clinical trials to examine the therapeutic potential to replace currently employed agents in acute and chronic heart failure patients. Molecular mechanisms of action of Ca(2+) sensitisers are divergent. In addition, they show a wide range of discrete pharmacological profiles due to additional actions associated with individual compounds. Therefore, the outcome of clinical trials has to be explained carefully based on these mechanisms of actions.

Mechanisms of action of novel cardiotonic agents

Regulation of myocardial contractility by cardiotonic agents is achieved by an increase in intracellular Ca2+ mobilization (upstream mechanism), an increase in Ca2+ binding affinity to troponin C (central mechanism), or facilitation of the process subsequent to Ca2+ binding to troponin C (downstream mechanism). cAMP mediates the regulation induced by Ca2+ mobilizers such as beta-adrenoceptor agonists and selective phosphodiesterase III inhibitors acting through the upstream mechanism. These agents act likewise on the central mechanism to decrease Ca2+ sensitivity of troponin C in association with the cAMP-mediated phosphorylation of troponin I. In addition to such a well-known action of cAMP, recent experimental findings have revealed that Ca2+ sensitizers, such as levosimendan, OR-1896, and UD-CG 212 Cl, require the cAMP-mediated signaling for induction of Ca2+ sensitizing effect. These agents shift the [Ca2+] -force relationship to the left, but their positive inotropic effect (PIE) is inhibited by carbachol, which suppresses selectively the cAMP-mediated PIE. These findings imply that cAMP may play a crucial role in increasing the myofilament Ca2+ sensitivity by cross-talk with the action of individual cardiotonic agents. No clinically available cardiotonic agents act primarily via Ca2+ sensitization, but the PIE of pimobendan and levosimendan is partly mediated by an increase in myofilament Ca2+ sensitivity. Evidence is accumulating that cardiotonic agents with Ca2+ sensitizing action are more effective than agents that act purely via the upstream mechanism in clinical settings. Further clinical trials are required to establish the effectiveness of Ca2+ sensitizers in long-term therapy for congestive heart failure patients.

Cyclic nucleotide research -- still expanding after half a century

Since the discovery in 1957 that cyclic AMP acts as a second messenger for the hormone adrenaline, interest in this molecule and its companion, cyclic GMP, has grown. Over a period of nearly 50 years, research into second messengers has provided a framework for understanding transmembrane signal transduction, receptor-effector coupling, protein-kinase cascades and downregulation of drug responsiveness. The breadth and impact of this work is reflected by five different Nobel prizes.

Increase in myofibrillar Ca2+ sensitivity induced by UD-CG 212 Cl, an active metabolite of pimobendan, in canine ventricular myocardium

We performed experiments in canine ventricular trabeculae loaded with aequorin to elucidate the mechanism of positive inotropic effect of UD-CG 212 Cl (4,5-dihydro-6-[2-(4-hydroxyphenyl)-1H-benzimidazole-5-yl]-5-methyl-3(2H)-pyridazinone), an active metabolite of pimobendan. The maximum response to UD-CG 212 Cl achieved at 10(-5) M was 18% of ISOmax and it was associated with an increase in Ca2+ transients of 7% of ISOmax. For a given increase in force, the increase in Ca2+ transients induced by UD-CG 212 Cl was less than that induced by elevation of [Ca2+]o. The positive inotropic effect of UD-CG 212 Cl was not associated with an impairment of relaxation and it was abolished by carbachol. In conclusion, UD-CG 212 Cl has a positive inotropic effect partly due to an increase in myofibrillar Ca2+ sensitivity that is exerted via cross talk with a signal transduction pathway that involves cAMP.

Cilostazol, a selective type III phosphodiesterase inhibitor, decreases triglyceride and increases HDL cholesterol levels by increasing lipoprotein lipase activity in rats

Cilostazol, a selective type III phosphodiesterase inhibitor, has antiplatelet and vasodilating effects. In this study, the effects of cilostazol on lipid metabolism and lipoprotein lipase (LPL) activity were studied in rats. Cilostazol was administered orally at doses of 30 or 100 mg/kg twice a day for 1-2 weeks to rats. Cilostazol decreased the serum triglyceride level in normolipidemic rats. The serum triglyceride level was reduced and HDL cholesterol level was increased by cilostazol in streptozotocin (STZ)-induced diabetic rats. The disappearance of exogenous triglyceride was accelerated by cilostazol in normolipidemic rats. Cilostazol increased post-heparin plasma LPL activity but had no effect on hepatic triglyceride lipase activity in STZ-induced diabetic rats. Cilostazol also increased LPL activity in the heart in STZ-induced diabetic rats. These findings suggest that an increase in LPL activity is responsible for the serum triglyceride lowering and HDL cholesterol elevating effects of cilostazol in rats.

Inotropic effects of OR-1896, an active metabolite of levosimendan, on canine ventricular myocardium

We performed experiments in dog ventricular trabeculae loaded with aequorin to elucidate the mechanism of positive inotropic effect of (R)-N-[4-(4-methyl-6-oxo-1,4,5, 6-tetrahydro-pyridazin-3-yl)-phenyl]-acetamide (OR-1896), an active metabolite of (R)-([4-(1,4,5, 6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]-hydrazono)-pr opaned initrile (levosimendan). Concentration-response curve for OR-1896 was biphasic: positive inotropic effect of OR-1896 reached a plateau at 10(-5) M (1st phase) and the concentration-response curve became steeper at 10(-3) M and higher (2nd phase). Maximum response of the 1st phase was 29% of maximal response to isoproterenol and associated with an increase in Ca(2+) transients of 13% of the maximal response to isoproterenol. For a given increase in force, the increase in Ca(2+) transients by OR-1896 was lower than that induced by elevation of [Ca(2+)](o). The positive inotropic effect of OR-1896 was not associated with impairment of relaxation and it was abolished by carbachol. In conclusion, OR-1896 has a positive inotropic effect partly due to an increase in myofibrillar Ca(2+) sensitivity that is exerted via cross-talk with signal transduction mediated by cAMP.

Effects of OR-1896, an active metabolite of levosimendan, on contractile force and aequorin light transients in intact rabbit ventricular myocardium

We performed experiments in rabbit ventricular papillary muscles loaded with aequorin to elucidate the mechanism of positive inotropic effect (PIE) of OR-1896, an active metabolite of levosimendan. The concentration-response curve (CRC) for OR-1896 was biphasic: PIE of OR-1896 reached a plateau at 10(-5) M (first phase), and the CRC became steeper at 10(-3) M and higher (second phase). Maximal response of the first phase was 11% of the maximal response to isoproterenol (ISOmax) and associated with an increase in Ca2+ transients of 5% of ISOmax. For a given degree of PIE, the increase in Ca2+ transients by OR-1896 was lower than that induced by elevation of [Ca2+]o. The PIE of OR-1896 was not associated with impairment of relaxation, and it was abolished by carbachol. In conclusion, OR-1896 has a PIE partly due to an increase in myofibrillar Ca2+ sensitivity that is exerted through crosstalk with signal transduction mediated by cyclic adenosine monophosphate (cAMP).

Antiplatelet and antithrombotic effects of a novel selective phosphodiesterase 3 inhibitor, NSP-513, in mice and rats

We investigated the effects of NSP-513, (R)-4,5-dihydro-5-methyl-6-[4-(2-propyl-3-oxo-1-cyclohexenyl)amino] phenyl-3(2H)-pyridazinone, on phosphodiesterase (PDE) isozyme activities, in vitro platelet aggregation and in vivo thrombus formation. NSP-513 selectively inhibited human platelet PDE 3 isozyme with an IC50 value of 0.039 microM. In an in vitro human platelet aggregation assay, the IC50 values (microM) of NSP-513 for platelet aggregation induced by collagen, U-46619, arachidonic acid, adenosine diphosphate (ADP), epinephrine and thrombin were 0.31, 0.25, 0.082, 0.66, 0.23 and 0.73, respectively. In a mouse pulmonary thromboembolism model, orally administered NSP-513 showed in vivo antithrombotic effects that were 320 to 470 times more potent than those of cilostazol. In a rat carotid arterial thrombosis model, intraduodenally administered NSP-513 (0.1 mg/kg), cilostazol (30 mg/kg) and aspirin (30 mg/kg) reduced thrombus formation by 75%, 66% and 48%, respectively. However, intravenously administered dipyridamole (10 mg/kg) did not significantly prevent thrombus formation. These results demonstrate that NSP-513 has the potential to prevent not only in vitro platelet aggregation but also in vivo thrombus formation and indicate that the highly selective PDE 3 inhibitory effect of NSP-513 may make this compound useful for assessing the physiological role of PDE 3.

Stimulation of long-chain fatty acid uptake by dipyridamole in isolated myocytes

This study was designed to investigate the effects of the cardiovascular drug dipyridamole on fatty acid metabolism in isolated cardiac myocytes. Effects of dipyridamole on the oxidation of long-chain (palmitate) fatty acid, medium-chain (octanoate) fatty acid, and the carbohydrate intermediate (pyruvate) were determined by using isolated cardiac myocytes from both normal and diabetic rats. Dipyridamole increased palmitate oxidation in a concentration-dependent manner in both normal and diabetic myocytes. Maximal stimulation of palmitate oxidation (175% of control) was observed with 100 microM dipyridamole. In contrast, oxidation of octanoate and pyruvate was not affected. The stimulation of palmitate oxidation by dipyridamole persisted despite its removal from the incubation medium. In contrast to the effect in myocytes, palmitate oxidation was not affected by dipyridamole in isolated rat heart mitochondria. Palmitate uptake was increased by 2.5- and 1.6-fold when palmitate concentration was adjusted to 0.05 and 0.2 mM, respectively. Dipyridamole did not affect lipolysis in isolated myocytes. When dipyridamole (100 microM) and L-carnitine (5 mM) were added together to the incubation medium, palmitate oxidation was further increased to 223% of the control. The nucleoside transport inhibitor nitrobenzylthioinosine (NBMPR) failed to increase palmitate oxidation in isolated myocytes. Although palmitate oxidation in diabetic cells is much higher than that in normal myocytes, dipyridamole increased palmitate oxidation by 243% in diabetic myocytes over its baseline oxidation rate in normal cells. These results suggest that increased palmitate oxidation in isolated cardiac myocytes after dipyridamole administration occurs independent of effects on either the phosphodiesterase enzyme or nucleoside transport protein, but it may result from increased palmitate transport across the plasma membrane.

Catecholaminergic modulation of respiratory rhythm in an in vitro turtle brain stem preparation

An in vitro brain stem preparation from adult turtles was used to determine effects of dopamine (DA) and norepinephrine (NE) on the pattern of respiratory motor output recorded from hypoglossal nerve roots (XII). Bath-applied DA (10-200 microM) increased the frequency of respiratory bursts (peaks) from 0.9 +/- 0.2 to 2.4 +/- 0.3 (SE) peaks/min, resulting in a 99 +/- 9% increase in neural minute activity. R[+]-SCH-23390 (10 microM, D1 antagonist) and eticlopride (20 microM, D2 antagonist) attenuated the DA-mediated increase in peak frequency by 52 and 59%, respectively. On the other hand, the DA-receptor agonists apomorphine (D1, D2), quinelorane (D2), and SKF-38393 (D1) had no effect on peak frequency. Prazosin, an alpha1-adrenergic antagonist (250 nM) abolished the DA-mediated frequency increase. Although NE (10-200 microM) and phenylephrine (10-200 microM, alpha1-adrenergic agonist) increased peak frequency from 0.5 +/- 0.1 to 1.2 +/- 0.3 peaks/min and from 0.6 +/- 0.1 to 1. 0 +/- 0.2 peaks/min, respectively, these effects were not as large as that with DA alone. The data suggest that both dopaminergic and adrenergic receptor activation in the brain stem increase respiratory frequency in turtles, but the DA receptor-mediated increase is dependent on coactivation of alpha1-adrenergic receptors.

The effect of cilostazol, a cyclic nucleotide phosphodiesterase III inhibitor, on heparin-binding EGF-like growth factor expression in macrophages and vascular smooth muscle cells

Heparin-binding EGF-like growth factor (HB-EGF) is a mitogen for smooth muscle cells (SMC) and is detected in SMC and macrophages in atherosclerotic plaques, suggesting that HB-EGF may be associated with the pathogenesis of atherosclerosis. The present study indicates that cilostazol, a phosphodiesterase III inhibitor, suppresses the expression of HB-EGF in rat aortic SMC and in U-937 cells, a macrophage-like cell line, stimulated by lipopolysaccharide. Further, cilostazol diminished the induction of HB-EGF mRNA by methylglyoxsal, which is a reactive dicarbonyl metabolite produced as the result of a glycation reaction and which might be associated with macroangiopathy caused by hyperglycemia. Cilostazol suppressed the production of HB-EGF protein in the conditioned medium of SMC. These data suggest that cilostazol might act by suppressing the progression of atherogenesis by means of suppressing the expression of HB-EGF in SMC and macrophages.

A mathematical model for analysis of pharmacologically induced changes in the kinetics of cardiac muscle

A mathematical model of the isometric contraction of cardiac muscle is developed and utilized to characterize the inotropic and lusitropic effects of cardioactive compounds in isolated guinea pig left atria. In contrast to metrics that are based on minima and maxima of an isometric twitch and its derivative function, the entire time course of the twitch is used to quantify the kinetics of the contraction-relaxation cycle. The model relates observed tension to a time-dependent activation function that describes generation of internal force and a coupling function that determines mechanical response to the activation function. The model is structured so that it is suitable for nonlinear curve fitting to observed data. Results obtained using the model for fitting experimental data from tissues treated with different classes of cardioactive compounds agree with more qualitative results presented by other authors. Experiments using the model to fit data over an extended (90 min) time course revealed differences in the kinetic profiles of milrinone and forskolin. Computer simulations that demonstrate the effect of each model parameter on twitch kinetics are presented, and the relationships between the model and other theoretical and empirical models of cardiac muscle are discussed. The mathematical model is useful to enable a more quantitative understanding of the kinetics of cardiac muscle contraction and relaxation and identify compounds that may be selective for inotropic or lusitropic effects.

E-1020, a water soluble imidazopyridine, has direct effects on Ca(2+)-dependent force and ATP hydrolysis of canine and bovine cardiac myofilaments

E-1020 is a cardiotonic agent that acts as a cyclic-AMP phosphodiesterase inhibitor but also may have actions which alter myofilament response to Ca2+. To identify direct actions of E-1020 on cardiac contractile proteins, effects of E-1020 on myofibrillar Ca2+ dependent MgATPase and force generation in chemically skinned fiber bundles were measured. In bovine cardiac myofibrils, E-1020 (100 microM) significantly increased myofilament Ca2+ sensitivity and Ca(2+)-dependent ATPase activity at submaximal pCa values. At pCa 6.75, E-1020 significantly increased ATPase activity in bovine (10-100 microM) and canine (1-100 microM) cardiac myofibrils but had no effect on rat cardiac myofibrils. Moreover, in one population of canine ventricular fiber bundles, E-1020 (0.01-10 microM) significantly increased isometric tension at pCa 6.5 and 6.0, whereas in another population of bundles E-1020 had no effect on tension. In no case was resting (pCa 8.0) or maximal tension (pCa 4.5) increased by E-1020. Measurements of Ca2+ binding to canine ventricular skinned fiber preparations demonstrated that E-1020 does not alter the affinity of myofilament troponin C for Ca2+. We conclude that part of the mechanism by which E-1020 acts as an inotropic agent may involve alterations in the responsiveness of contractile proteins to Ca2+. The lack of effect of E-1020 on some preparations may be dependent on isoform populations of myofilament proteins.

Milrinone: basic and clinical pharmacology and acute and chronic management

Milrinone (Inocor-Sanofi-Winthrop) represents a second generation phosphodiesterase inhibitor currently approved for intravenous administration in the treatment of decompensated congestive heart failure. By inhibiting Type III phosphodiesterase, milrinone increases intracellular cyclic adenosine monophosphate. This results in a positive inotropic effect on the heart and vasodilatation in the periphery. The hemodynamic consequences of this action produce left ventricular afterload reduction, with an increase in cardiac output and a reduction in total peripheral resistance. Unlike the sympathomimetic amines, milrinone produces no tolerance and possesses the distinct advantage of directly decreasing pulmonary vascular resistance. Short-term intermittent infusion by peripheral administration, continuous infusion, long-term therapy, and intermittent outpatient therapy was demonstrated to be safe, efficacious, and cost effective. It is hypothesized that intravenous milrinone, by producing biventricular afterload reduction, offers an efficacious, cost-effective tool for the treatment of decompensated heart failure.

Mechanical and electrophysiological effects of a hydroxyphenyl-substituted tetrahydroisoquinoline, SL-1, on isolated rat cardiac tissues

The mechanisms of the positive inotropic action of a new synthetic tetrahydroisoquinoline compound, SL-1, were investigated in isolated rat cardiac tissues and ventricular myocytes. SL-1 produced a rapidly developing, concentration-dependent positive inotropic response in both atrial and ventricular muscles and a negative chronotropic effect in spontaneously beating right atria. The positive inotropic effect was not prevented by pretreatment with reserpine (3 mg/kg) or the alpha-adrenoceptor antagonist prazosin (1 microM), but was suppressed by either the beta-adrenoceptor antagonist atenolol (3 microM) or the K+ channel blocker 4-aminopyridine (4AP, 1mM). In the whole-cell recording study, SL-1 increased the plateau level and prolonged the action potential duration in a concentration-dependent manner and decreased the maximum upstroke velocity (Vmax) and amplitude of the action potential in isolated rat ventricular myocytes stimulated at 1.0 Hz. On the other hand, SL-1 had little effect on the resting membrane potential, although it caused a slight decrease at higher concentrations. Voltage clamp experiments revealed that the increase of action potential plateau and prolongation of action potential duration were associated with an increase of Ca2+ inward current (ICa) via the activation of beta-adrenoceptors and a prominent inhibition of 4AP-sensitive transient outward K+ current (Ito) with an IC50 of 3.9 microM. Currents through the inward rectifier K+ channel (IK1) were also reduced. The inhibition of Ito is characterized by a reduction in peak amplitude and a marked acceleration of current decay but without changes on the voltage dependence of steady-state inactivation. In addition to the inhibition of K+ currents, SL-1 also inhibited the Na+ inward current (INa) with an IC50 of 5.4 microM, which was correlated with the decrease of Vmax. We conclude that the positive inotropic effect of SL-1 may be due to an increase in Ca2+ current mediated via partial activation of beta-adrenoceptors and an inhibition of K+ outward currents and the subsequent prolongation of action potentials.

Effects of a novel cardiotonic agent, Org 9731, on force and aequorin light transients in intact ventricular myocardium of the dog: involvement of a cyclic AMP-mediated mechanism and myofibrillar responsiveness to Ca2+ ions

The action of a novel cardiotonic agent, Org 9731 (4-fluoro-N-hydroxy-5, 6-dimethoxy-benzo[b]thiophene-2-carboximidamide methanesulphonate), on intracellular aequorin light transients and isometric contractions was investigated in ventricular trabeculae isolated from dogs. The positive inotropic effect of Org 9731 at 3 microM and higher (up to 0.1 mM) was associated with an increase in the amplitude of the intracellular Ca2+ transient, but the effect of the compound at 0.3 and 1 mM was accompanied by a decrease of the transient. The maximum inotropic response to Org 9731 was approximately 70% of the maximum response to isoproterenol, while the maximum increase in the amplitude of Ca2+ transients produced by Org 9731 was about 30% of the maximum increase induced by isoproterenol. The duration of isometric contractions was prolonged by Org 9731 at 0.3 and 1 mM, with accompanying prolongation of the duration of light transients. The concentration-response curve for the positive inotropic effect of Org 9731 was markedly shifted by carbachol (3 microM), being moved to the right and downward, and the maximum response to Org 9731 was about 10% of that to isoproterenol in the presence of carbachol. Carbachol abolished the increase in the light transient and the accumulation of adenosine 3',5'-cyclic monophosphate (cyclic AMP) induced by Org 9731. These results indicate that Org 9731 increases cardiac contractility, mainly through the accumulation of cyclic AMP up to a concentration of 0.1 mM and also by increasing the responsiveness of myofibrils to Ca2+ ions at 0.3 mM and higher in association with the attenuation of Ca2+ transients. The structure-activity relationship implies that the introduction of a fluorine atom at position 4 of the benzothiophene ring of Org 30,029 attenuated its Ca(2+)-sensitizing action but markedly increased the activity of mechanisms dependent on cyclic AMP.

The effects of various drugs on the myocardial inotropic response

1. The signal transduction process mediated by cyclic AMP that leads to the characteristic positive inotropic effect (PIE) in association with a positive lusitropic effect (acceleration of rate of twitch relaxation) has been well established. Relationships between accumulation of cyclic AMP, changes in intracellular Ca2+ transients and the PIE differ, however, depending on the mechanism of particular drugs that affect different steps in the metabolism of cyclic AMP. Selective partial agonists of beta 1-adrenoceptors and inhibitors of phosphodiesterase (PDE) III cause the accumulation of less cyclic AMP for a given PIE than does isoproterenol. In addition, in aequorin-microinjected canine ventricular muscle, selective inhibitors of PDE III, OPC 18790 and Org 9731, produced smaller decreases in the responsiveness of myofilaments to Ca2+ ions than isoproterenol, while a partial agonist of beta 1-adrenoceptors, denopamine, elicits a decrease in Ca2+ responsiveness of the same extent as does isoproterenol. 2. Activation of myocardial alpha 1-adrenoceptors, as well as stimulation of receptors for endothelin and angiotensin II, which accelerates hydrolysis of phosphoinositide (PI) to result in production of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) are associated with very similar inotropic regulation: (1) the dependence on the species of animals of induction of the PIE; (2) an excellent correlation between the extent of acceleration of hydrolysis of PI and the PIE; (3) isometric contraction curves associated with a negative lusitropic effect; (4) the PIE associated with increases in myofibrillar responsiveness to Ca2+ ions; and (5) the selective inhibition of the PIE by an activator of protein kinase C (PKC), phorbol 12,13-dibutyrate (PDBu), with little effect on the PIE of isoproterenol and Bay k 8644. 3. A novel class of cardiotonic agents, namely, Ca2+ sensitizers such as EMD 53998 and Org 30029, act on the Ca(2+)-binding site of troponin C, increasing the affinity of these sites for Ca2+ ions, or at the actin-myosin interface to facilitate the cycling of cross-bridges. These agents produce a PIE with little change or decrease in Ca2+ transients and may bring about a significant breakthrough in the development of drugs for reversal of myocardial failure in the treatment of congestive heart failure.

Mechanical and electrophysiological studies on the positive inotropic effect of 2-phenyl-4-oxo-hydroquinoline in rat cardiac tissues

1. The pharmacological and electrophysiological effect of 2-phenyl-4-oxo-hydroquinoline (YT-1), a new synthetic agent, were determined in rat isolated cardiac tissues and ventricular myocytes. 2. YT-1 was found to have a positive inotropic effect in both atria and ventricular muscles but did not cause significant increases in the spontaneously beating rate of right atria. 3. The positive inotropic effect of YT-1 was antagonized neither by beta-nor by alpha-adrenoceptor antagonists but was partially antagonized by a Ca2+ channel blocker (verapamil) and a K+ channel blocker (4-AP). 4. The action potential duration and amplitude of ventricular cells were progressively increased as the concentration of YT-1 was increased from 3 to 30 microM. 5. A voltage clamp study revealed that the prolongation of action potential duration by YT-1 was associated with a prominent inhibition of 4-AP-sensitive transient outward current (I(to)). At potentials negative to the reversal potential of K1-channels, the inward current through these channels was partially reduced by YT-1. At potentials positive to the reversal potential, the outward current through these channels was affected very little. 6. Although YT-1 blocked the amplitude of I(to), the voltage-dependence of the steady-state inactivation of I(to), was unaffected. 7. Apart from the inhibition of K+ currents, YT-1 also inhibited the sodium inward current. 8. The evidence suggests that YT-1 increases the slow inward Ca2+ current (ICa) significantly. 9. It is concluded that the positive inotropic effect of YT-1 is due predominantly to the increase of ICa and inhibition of I(to).

The role of phosphodiesterase inhibitors in heart failure

Myocardial contractility is dependent on available intracellular calcium and this can be enhanced by increasing intracellular cyclic adenosine monophosphate. One way of achieving this is by inhibiting the phosphodiesterase III enzyme. Over the last 15 years, a number of new drugs with this mechanism of action have been studied in man and have been found not only to have a positive inotropic action on the heart but also a vasodilating action on peripheral blood vessels. This combination of effects produces favourable haemodynamic improvement in patients with chronic heart failure. While some smaller studies showed that this did translate into an improvement in symptoms and functional capacity, a large well-designed and controlled clinical trial showed that survival was decreased when milrinone was used in target daily doses of 40 mg. For this reason, chronic long-term oral therapy with phosphodiesterase III inhibitors is not currently being actively pursued. They may still have a role as acute short-term therapy in severely ill patients who do not respond adequately to optimal standard drug therapy. Milrinone has been one of the most widely studied drugs in this regard. Even during short-term administration, its use should be closely monitored for any evidence of an increase in ventricular arrhythmias or decrease in ventricular function.

Cardiotoxicity of vasodilators and positive inotropic/vasodilating drugs in dogs: an overview

Standard toxicological studies in dogs using high doses of vasodilators and positive inotropic/vasodilating agents give rise to a species-specific cardiotoxicity. The reason may be the extreme sensitivity of the dog to the pharmacological effects of these drugs; exaggerated pharmacodynamic effects and prolonged disturbance of homeostasis mechanisms often are responsible for the observed organ lesions. An assessment of the toxicological relevance and the risk for patients taking the drugs at therapeutic doses cannot be made without taking into account their pathomechanisms and the pathophysiological basis of the exceptional reaction patterns occurring in dogs. A large series of vasodilating and positive inotropic agents are presented, their pharmacological properties are described, and toxicological effects in dogs are compared. In view of the poor correlation between the distinct cardiac lesions induced in dogs and a lack of comparable toxicity in humans, it appears desirable to reassess the adequacy of the standard toxicological approaches for these substances.

Improved heart failure protection by FK664, a novel positive inotropic agent, in dog heart-lung preparations

The effects of FK664, a novel positive inotropic agent, and enoximone on pentobarbital-induced heart failure were compared in dog heart-lung preparations. Both FK664 and enoximone improved the cardiac function curve in a dose-dependent manner and restored it to the control level at drug concentrations of 1 microgram/ml and 10 micrograms/ml, respectively. Therefore, the cardiotonic potency of FK664 appears to be 10 times that of enoximone. These agents were almost equal in force-rate separation of cardiac effect. Neither of the agents produced arrhythmia at any dose tested. These results suggest that FK664 may be a potent cardiotonic agent for the treatment of heart failure.

The effect of FK664, a new cardiovascular drug, on systemic capacitance vessels in anesthetized dogs

To characterize the cardiovascular effect of FK664, a compound developed for the treatment of heart failure, the mean circulatory pressure (MCP), cardiac output and other parameters were measured in open-chest anesthetized dogs. Milrinone, a cardiotonic agent, and nifedipine, a calcium channel blocker were used as reference substances. Nifedipine (10 micrograms/kg), FK664 (0.1 mg/kg) or milrinone (0.1 mg/kg) given intravenously reduced the total peripheral resistance in a similar extent (35-40%). Whereas nifedipine had no effect on MCP, FK664 produced a significant decrease in MCP. Milrinone caused a minimal decrease in MCP, but not significantly. These results indicate that FK664 dilates the systemic capacitance vessels. This action to reduce the pre-load would be beneficial in the treatment of heart failure.

The effect of pimobendan on myocardial mechanical function and metabolism in dogs: comparison with dobutamine

The effect of pimobendan, a newly developed cardiotonic agent, on myocardial mechanical function and energy metabolism has been examined in the dog heart, and compared with that of dobutamine. Either saline, vehicle for pimobendan, dobutamine (0.3 and 1 microgram kg-1), or pimobendan (0.3 and 1 mg kg-1) was injected intravenously. Dobutamine and pimobendan both increased the first derivative of left ventricular pressure and percent segment shortening, indicating their positive inotropic action. After 2 min of dobutamine injection, or after 20 min of pimobendan injection, the myocardium was removed, and used for determination of the tissue levels of metabolites of energy and carbohydrate metabolism. In general, all metabolic parameters measured were not changed by either dobutamine or pimobendan injection. In animals with aortic constriction for 10 months, dobutamine and pimobendan injections did not alter the myocardial energy and carbohydrate metabolism. Although dobutamine and pimobendan increased the cardiac mechanical function, they did not disturb the myocardial energy and carbohydrate metabolism.

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)

Stimulation of fatty acid oxidation in myocytes by phosphodiesterase inhibitors and adenosine analogues

The effect of various phosphodiesterase inhibitors, and adenosine analogues on palmitate oxidation, were studied in isolated rat myocytes. Enoximone, milrinone, and dipyridamole, at a concentration of 250 microM, stimulated palmitate oxidation by 78%, 40%, and 43%, respectively. The specific A1-agonist, N6-cyclopentyladenosine, increased palmitate oxidation by 56%, at a concentration of 250 microM. Moreover, the nucleoside transport inhibitor, S-(P-Nitrobenzyl-)6-thioinosine, increased palmitate oxidation by 40%, at a concentration of 100 microM. These data suggest that the stimulation of palmitate oxidation by enoximone and adenosine analogues may be mediated via the inhibition of the uptake and/or the oxidation of glucose in myocytes.

Effects of vanadate in testicular capsule of the rat

1. The effects of sodium orthovanadate (vanadate. 10(-5) to 3 x 10(-4) M) on testicular capsule of the rat, and the modifications of these effects by the calcium chelator EGTA (2mM), the calcium entry blockers verapamil (5 X 10(-5) M), nifedipine (10(-5 M) and diltiazem (5 x 10(-5) M), the (Na+ + K+)-ATPase inhibitor ouabain, the Na+/Ca2+ exchange inhibitor amiloride, and the calmodulin antagonists trifluoperazine (10(-4) M) and W-7 (5 x 10(-5) M) have been studied. 2. Vanadate induced contraction of the rat testicular capsule in a dose-dependent way (ED50: 82.8 +/- 7.4 x 10(-6) M). 3. The contraction induced by vanadate (3 and 30 x 10(-5) M) were abolished by EGTA and not modified by verapamil, nifedipine, flunarizine or diltiazem. 4. Amiloride (1 and 5 x 10(-5) M), but not ouabain (5 x 10(-5) and 10(-4) M), inhibit in a dose-dependent way the contraction induced by two doses of vanadate (3 and 30 x 10(-5) M). 5. Trifluoperazine and W-7 significantly inhibit the contraction of testicular capsule to 3 and 30 x 10(-5) M vanadate.

Stimulation of polyunsaturated fatty acid oxidation in myocytes by regulating its cellular uptake. On the rate limiting step of polyunsaturated fatty acid oxidation in heart

In order to investigate the regulation of polyunsaturated fatty acid oxidation in the heart, the effect of the phosphodiesterase inhibitor enoximone on the oxidation of [1-14C] arachidonic acid, and [1-14C] arachidonyl-CoA, were studied in adult rat myocytes, and isolated rat heart mitochondria. Enoximone stimulated arachidonate oxidation by 94%, at a concentration of 0.25 mM. The apparent Vmax value of arachidonate oxidation in the presence of enoximone (6.98 nmol/mg protein/30 min), was approximately 75% higher than the value observed with the control (4.0 nmol/mg protein/30 min) in isolated myocytes. Also, enoximone stimulated arachidonate uptake by 27% at a concentration of 0.25 mM. On the other hand, enoximone had no effect on the oxidation of [1-14C] arachidonyl-CoA in isolated rat heart mitochondria. These results suggest that the oxidation of polyunsaturated fatty acids in myocytes is regulated by the rate of uptake of these acids across sarcolemmal membranes.

Effect of amrinone on anthracycline-induced lethal and cardiac toxicity in mice and rats

The protective role of amrinone against toxicity of anthracyclines was examined in both mice and rats. These two anthracyclines were selected since they are characterized by different patterns of toxicity. In contrast to doxorubicin, the 4'-deoxy derivative did not cause delayed mortality. The results of this investigation indicate that amrinone is an effective protective agent against acute lethal events induced by both anthracyclines. However, the inotropic agent did not reduce the delayed mortality produced by doxorubicin. This parallels the apparent lack of prevention of doxorubicin-induced myocardial toxicity in CD rats, as determined by ECG changes and by morphologic alterations following multiple drug administrations. The administration of amrinone did not interfere with the antitumor activity of 4'-deoxy-doxorubicin against C-26 colon tumor.

Effects of a new 1,3-thiazole derivative ZSY-39 on force of contraction and cyclic AMP content in canine ventricular muscle

A newly synthesized 1,3-thiazole derivative ZSY-39 increased the force of contraction in a concentration-dependent manner in association with elevation of tissue cyclic AMP levels in the isolated canine ventricular trabeculae electrically driven at 0.5 Hz at 37 degrees C. ZSY-39 shortened the duration of isometric contractions mainly by abbreviation of the relaxation time. The maximal response to and EC50 of ZSY-39 were 0.7 (isoproterenol = 1.0) and 4.6 x 10(-5) M. Bupranolol (3 x 10(-7) M) did not affect the positive inotropic effect of ZSY-39. The time course of increases in the force of contraction induced by ZSY-39 (10(-4) M) coincided with that of cyclic AMP accumulation. The concentration-response curve for the increase in the force of contraction produced by ZSY-39 was superimposable on that of the elevation of cyclic AMP levels. Carbachol (3 x 10(-6) M) shifted the concentration-response curve for the increase in force by ZSY-39 to the right and downward, and decreased the accumulation of cyclic AMP induced by ZSY-39 (10(-4) M). ZSY-39 (10(-5) M) enhanced significantly the positive inotropic effect of isoproterenol. The relationship between the force of contraction and cyclic AMP levels after the administration of ZSY-39 was not modified by the addition of carbachol or isoproterenol. These findings indicate that cyclic AMP plays an important role in the positive inotropic effect of ZSY-39 on canine ventricular muscle.

Identification and selective inhibition of four distinct soluble forms of cyclic nucleotide phosphodiesterase activity from kidney

Homogenization of rat kidney under isotonic conditions and in the presence of protease inhibitors showed that some 92% of the cyclic AMP phosphodiesterase activity and some 83% of the cyclic GMP phosphodiesterase activity was released into the soluble fraction. Analysis of soluble phosphodiesterase activity by FPLC on a Mono-Q column resolved four distinct fractions expressing cyclic nucleotide phosphodiesterase activity. Lineweaver-Burk plots for the hydrolysis of both cyclic GMP and cyclic AMP yielded linear results. The first two peaks (KPDE-MQ-II, KPDE-MQ-III) showed higher activities towards cyclic GMP than cyclic AMP with the ratio of their Vmax values for the hydrolysis of cyclic AMP/cyclic GMP being 0.66 and 0.16, respectively. For the second two peaks (KPDE-MQ-IV, KPDE-MQ-V) the Vmax ratios for the hydrolysis of cyclic AMP/cyclic GMP were 6.4 and 16.7, respectively. All enzymes exhibited similar low Km values for both cyclic AMP and cyclic GMP but had very different Vmax values. KPDE-MQ-II was activated by Ca2+/calmodulin. The cyclic AMP phosphodiesterase activity of KPDE-MQ-III was augmented by the presence of low concentrations of cyclic GMP. Thermal denaturation studies showed that the phosphodiesterase activity of each fraction decayed as a single exponential indicating that each phosphodiesterase fraction contained but a single phosphodiesterase activity. The inhibitors IBMX, zaprinast, milrinone, amrinone, buquineran, carbazeran, ICI 118233, ICI 63197 exerted selective effects on the activities of these enzymes. We compared the action of these compounds on cyclic GMP phosphodiesterases from bovine retina. Over the concentration ranges used, the bovine retinal enzyme was only inhibited by IBMX, zaprinast and carbazeran. The cytosolic isoenzymes of cyclic AMP phosphodiesterases play a much more important role in metabolizing cyclic AMP in kidney compared with liver, where the activity of membrane-bound isoenzymes predominate.

Chronotropic and inotropic actions of amrinone, carbazeran and isobutylmethyl xanthine: role of phosphodiesterase inhibition

1. The chronotropic and inotropic effects of amrinone, carbazeran and 3-isobutyl-1-methyl xanthine (IBMX) were examined in isolated preparations of papillary muscle and right atria from rabbit heart. The effects of the drugs on cardiac phosphodiesterase and cyclic nucleotide content were also examined. 2. Amrinone (2.4 x 10(-4)M-2 x 10(-3) M), carbazeran (9.1 x 10(-6) M-1.2 x 10(-3) M), and IBMX (1.8 x 10(-5) M-4.5 x 10(-4) M) produced concentration-dependent positive inotropic responses of papillary muscle preparations, the rank order of potency being carbazeran = IBMX greater than amrinone. Sub-threshold positive inotropic concentrations of all three compounds potentiated the positive inotropic effects of isoprenaline; leftward shifts in the concentration-effect curves were 5 fold (IBMX), 11 fold (amrinone) and 46 fold (carbazeran). 3. Amrinone and IBMX produced concentration-dependent positive chronotropic responses in isolated right atria and showed a similar rate selectivity to isoprenaline, but carbazeran elicited a decrease in beating frequency. None of these drugs potentiated the positive chronotropic effects of isoprenaline. 4. Concentrations of amrinone, carbazeran and IBMX that produced similar positive inotropic responses were associated with different increases in papillary muscle cyclic AMP and cyclic GMP concentrations. 5. All three compounds inhibited right atrial and ventricular phosphodiesterase, with amrinone being the least potent. There was, however, a marked difference between the IC50 and EC50 values for phosphodiesterase inhibition and positive inotropy. In contrast the positive chronotropic effects of amrinone and IBMX were observed in the same concentration ranges that produced phosphodiestrease inhibition. 6. The results indicate that amrinone possesses a similar rate/force selectivity to isoprenaline and IBMX. In contrast, carbazeran exerts both positive inotropic and negative chronotropic effects. Phosphodiesterase inhibition and elevation of intracellular cyclic AMP concentration may be involved, at least in part, in the cardiac effects of these drugs.

Hemodynamic effects of pimobendan given orally in congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

Pimobendan (UD-CG 115 BS) was administered orally to 23 patients with congestive heart failure (functional class IV) caused by coronary artery disease (11 patients) or idiopathic dilated cardiomyopathy (12). All patients received maintenance doses of digoxin, furosemide and warfarin. Baseline data, collected during 15 hours, stayed within a 10% range. A 10-mg oral dose of pimobendan increased the heart rate from 95 +/- 20 to 109 +/- 24 beats/min (p less than 0.003). The pulmonary artery wedge pressure decreased from 23.0 +/- 5.9 to 10.1 +/- 5.2 mm Hg (p less than 0.0001), the cardiac index increased from 1.9 +/- 0.4 to 3.3 +/- 0.7 liters/min/m2 (p less than 0.0001) and the left ventricular stroke work index increased from 2,005 +/- 927 to 3,065 +/- 1,161 ml/mm Hg/m2 (p less than 0.0001). Statistically significant improvements in hemodynamic variables were still present 10 hours after the administration of pimobendan. Most patients felt better and reported no angina or other side effect, the incidence of ventricular arrhythmias was unchanged and no electrocardiographic changes suggesting ischemia were observed. Patients with severe congestive heart failure experienced a prolonged improvement of their cardiovascular condition after a single dose of pimobendan.

Can new inodilators displace digitalis in the therapy of congestive heart failure?

New inodilators that possess both positive inotropic and vasodilator actions have many favorable effects in patients with congestive heart failure, even in those with refractory heart failure. These effects are expected to prevent myocardial injury, improve peripheral circulation, depress the excessive endogenous neurohumoral activation, and, finally, improve the quality of life, and increase lifespan. However, experience with new inodilators has only begun. Several questions remain to be answered before these drugs can be widely used with safety, including whether life-threatening adverse effects appear, mortality rate is lessened, and drug tolerance occurs. The therapeutic level of the dose and the relation between the effectiveness of the drug and the degree of the severity of heart failure should also be established. Therefore, long-term, randomized, double-blind, placebo-controlled clinical trials will be necessary before the new inodilators can take the place of digitalis and thus become the mainstay of the therapy of congestive heart failure.

Pharmacokinetic profile of OPC-8212 in humans: a new, nonglycosidic, inotropic agent

OPC-8212, a new inotropic agent, was administered orally as a single 7.5-, 15-, 30-, 60-, 120-, or 240-mg dose in a sequentially ascending order to 21 male healthy volunteers to determine the pharmacokinetic profile. Each volunteer received one of the six doses after an overnight fast. After the single-dose study was completed and the safety and tolerability were ascertained, 3 of the 21 volunteers participated in a 15-day repeated-dose (30 mg once daily) study to determine the steady-state kinetic profile. The AUC0-infinity and Cmax values were proportional to doses (mg or mg/kg, P less than .001). The mean elimination t1/2, apparent oral clearance (CL/F) and percentage fraction of dose excreted unchanged in urine up to 336 hours postdose (fe0-336) appeared to be comparable among the six single doses examined. The overall mean (+/- SEM) kinetic parameters obtained from the 21 subjects were: 44.7 +/- 1.2 hours for t1/2, 0.284 +/- 0.018 L/hr or 4.49 +/- 0.28 mL/hr/kg for CL/F, and 17.7 +/- 0.9% for fe0-336. A steady state of the drug appeared to be attained by about day 9 after the initiation of the repeated dosing: the mean postdose 2- and 24-hour plasma drug concentrations observed during days 9 to 15 ranged from 6.3 +/- 0.5 micrograms/mL to 6.9 +/- 0.6 micrograms/mL and from 3.6 +/- 0.7 micrograms/mL to 4.0 +/- 0.6 micrograms/mL, respectively. The mean fraction of the daily dose excreted unchanged in urine over the dosing interval (fe0-r) during days 9 to 15 ranged from 19.2 +/- 1.4% to 25.6 +/- 0.6%.(ABSTRACT TRUNCATED AT 250 WORDS)

Serial evaluation of left ventricular function in congestive heart failure by measurement of peak aortic blood acceleration

Peak acceleration of blood in the ascending aorta, an index of global systolic left ventricular (LV) function, can be measured noninvasively using a continuous wave Doppler velocimeter applied suprasternally. The feasibility of this approach as a tool for detecting improvement of LV function was studied in 16 patients with congestive heart failure (CHF). Measurements were made daily for 6 consecutive days. The daily variability of peak acceleration examined in 11 normal subjects was +/- 2 m/s/s. In 11 of 16 patients with CHF, peak acceleration increased more than 2 m/s/s by day 6 compared with day 1 (group 1). In 5 of 16 patients, peak acceleration remained unchanged (group 2). In group 1, peak acceleration was 11 +/- 1 m/s/s on day 1 and increased to 16 +/- 1 m/s/s on day 6 (p less than 0.001). In this group, CHF resolved by day 6 in 9 of 11 patients. In group 2, peak acceleration was 9 +/- 1 m/s/s on day 1 and remained unchanged through day 6. In these 5 patients, the signs and symptoms of CHF persisted through day 6. The results suggest that peak acceleration measured noninvasively with continuous wave Doppler can detect improvement of LV function in patients with CHF. The approach provides a simple and reliable bedside means for serial evaluation of LV systolic function.