Identification and characterization of isoenzymes of cyclic nucleotide phosphodiesterase in human kidney and heart, and the effects of new cardiotonic agents on these isoenzymes

Cyclic GMP and PKG Signaling in Heart Failure

Cyclic guanosine monophosphate (cGMP), produced by guanylate cyclase (GC), activates protein kinase G (PKG) and regulates cardiac remodeling. cGMP/PKG signal is activated by two intrinsic pathways: nitric oxide (NO)-soluble GC and natriuretic peptide (NP)-particulate GC (pGC) pathways. Activation of these pathways has emerged as a potent therapeutic strategy to treat patients with heart failure, given cGMP-PKG signaling is impaired in heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF). Large scale clinical trials in patients with HFrEF have shown positive results with agents that activate cGMP-PKG pathways. In patients with HFpEF, however, benefits were observed only in a subgroup of patients. Further investigation for cGMP-PKG pathway is needed to develop better targeting strategies for HFpEF. This review outlines cGMP-PKG pathway and its modulation in heart failure.

PDE2 at the crossway between cAMP and cGMP signalling in the heart

The cyclic nucleotides cAMP and cGMP are central second messengers in cardiac cells and critical regulators of cardiac physiology as well as pathophysiology. Consequently, subcellular compartmentalization allows for spatiotemporal control of cAMP/cGMP metabolism and subsequent regulation of their respective effector kinases PKA or PKG is most important for cardiac function in health and disease. While acute cAMP-mediated signalling is a mandatory prerequisite for the physiological fight-or-flight response, sustained activation of this pathway may lead to the progression of heart failure. In contrast, acute as well as sustained cGMP-mediated signalling can foster beneficial features, e.g. anti-hypertrophic and vasodilatory effects. These two signalling pathways seem to be intuitively counteracting and there is increasing evidence for a functionally relevant crosstalk between cAMP and cGMP signalling pathways on the level of cyclic nucleotide hydrolysing phosphodiesterases (PDEs). Among this diverse group of enzymes, PDE2 may fulfill a unique integrator role. Equipped with dual substrate specificity for cAMP as well as for cGMP, it is the only cAMP hydrolysing PDE, which is allosterically activated by cGMP. Recent studies have revealed strongly remodelled cAMP/cGMP microdomains and subcellular concentration profiles in different cardiac pathologies, leading to a putatively enhanced involvement of PDE2 in cAMP/cGMP breakdown and crosstalk compared to the other cardiac PDEs. This review sums up the current knowledge about molecular properties and regulation of PDE2 and explains the complex signalling network encompassing PDE2 in order to better understand the functional role of PDE2 in distinct cell types in cardiac health and disease. Moreover, this review gives an outlook in which way PDE2 may serve as a therapeutic target to treat cardiac disease.

Inhibition of phosphodiesterase 4 reduces ethanol intake and preference in C57BL/6J mice

Some anti-inflammatory medications reduce alcohol consumption in rodent models. Inhibition of phosphodiesterases (PDE) increases cAMP and reduces inflammatory signaling. Rolipram, an inhibitor of PDE4, markedly reduced ethanol intake and preference in mice and reduced ethanol seeking and consumption in alcohol-preferring fawn-hooded rats (Hu et al., 2011; Wen et al., 2012). To determine if these effects were specific for PDE4, we compared nine PDE inhibitors with different subtype selectivity: propentofylline (nonspecific), vinpocetine (PDE1), olprinone, milrinone (PDE3), zaprinast (PDE5), rolipram, mesopram, piclamilast, and CDP840 (PDE4). Alcohol intake was measured in C57BL/6J male mice using 24-h two-bottle choice and two-bottle choice with limited (3-h) access to alcohol. Only the selective PDE4 inhibitors reduced ethanol intake and preference in the 24-h two-bottle choice test. For rolipram, piclamilast, and CDP840, this effect was observed after the first 6 h but not after the next 18 h. Mesopram, however, produced a long-lasting reduction of ethanol intake and preference. In the limited access test, rolipram, piclamilast, and mesopram reduced ethanol consumption and total fluid intake and did not change preference for ethanol, whereas CDP840 reduced both consumption and preference without altering total fluid intake. Our results provide novel evidence for a selective role of PDE4 in regulating ethanol drinking in mice. We suggest that inhibition of PDE4 may be an unexplored target for medication development to reduce excessive alcohol consumption.

Population pharmacokinetics of olprinone in healthy male volunteers

BACKGROUND

Olprinone decreases the cardiac preload and/or afterload because of its vasodilatory effect and increases myocardial contractility by inhibiting phosphodiesterase III.

PURPOSE

The objective of this study was to characterize the population pharmacokinetics of olprinone after a single continuous infusion in healthy male volunteers.

METHODS

We used 500 plasma concentration data points collected from nine healthy male volunteers for the study. The population pharmacokinetic analysis was performed using the nonlinear mixed effect model (NONMEM®) software.

RESULTS

The time course of plasma concentration of olprinone was best described using a two-compartment model. The final pharmacokinetic parameters were total clearance (7.37 mL/minute/kg), distribution volume of the central compartment (134 mL/kg), intercompartmental clearance (7.75 mL/minute/kg), and distribution volume of the peripheral compartment (275 mL/kg). The interindividual variability in the total clearance was 12.4%, and the residual error variability (exponential and additive) were 22.2% and 0.129 (standard deviation). The final pharmacokinetic model was assessed using a bootstrap method and visual predictive check.

CONCLUSION

We developed a population pharmacokinetic model of olprinone in healthy male adults. The bootstrap method and visual predictive check showed that this model was appropriate. Our results might be used to develop the population pharmacokinetic model in patients.

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.

Bronchodilator effects of intravenous olprinone, a phosphodiesterase 3 inhibitor, with and without aminophylline in asthmatic patients

AIMS

There is no evidence demonstrating the clinical usefulness of phosphodiesterase (PDE) inhibitors in the treatment of asthma, although PDE3 and 4 inhibitors have received much attention for the treatment of bronchial asthma. We compared the bronchodilator effects of intravenously administered olprinone, a selective PDE3 inhibitor, and aminophylline, a nonselective PDE inhibitor, both alone and concomitantly.

METHODS

In 12 patients with mild stable asthma, we compared the acute bronchodilator effects of the following two drugs, alone and together using a double-blind crossover design: intravenous administration of olprinone, 30 micro g min-1; aminophylline, 2.25 mg min-1; and olprinone plus aminophylline over a total period of 150 min.

RESULTS

Mean maximal increase (95% confidence interval) in the FEV1 was 7.8% (2.4, 13.2), 17.1% (10.0, 24.2), 16.6% (11.2, 22.0), and 1.0% (-1.1, 3.1) during infusion of aminophylline, olprinone, aminophylline and olprinone, and saline, respectively. The magnitude of bronchodilatation produced by olprinone was greater than that by aminophylline. The combination of aminophylline and olprinone did not produce any greater bronchodilatation than olprinone alone. Olprinone alone or in combination with aminophylline lowered diastolic blood pressure, and increased heart rate.

CONCLUSIONS

These results suggest that the intravenous administration of PDE3 inhibitors exhibits a bronchodilatory effect. There are no additive or synergistic effects of administration of olprinone and aminophylline at the same time.

Type IV phosphodiesterase inhibition improves cardiac contractility in endotoxemic rats

Type IV phosphodiesterase inhibitors have a potential role in treating human sepsis. We examined the cardiac performance effects of type IV phosphodiesterase inhibition in vivo, in the absence and presence of catecholamines. Rats were randomized to receive either 4-(3-Butoxy-4-methoxybenzyl)imidazolidin-2-one (Ro 20-1724) at 0 (vehicle), 2 or 10 microg/kg/min. Utilizing a left ventricular catheter to measure cardiac performance, each animal received each of the two catecholamines, epinephrine and norepinephrine, in randomized order. Rats then received intravenous endotoxin and additional infusions of catecholamines. Ro 20-1724 at 2 microg/kg/min protected cardiac contractility during endotoxemia, and at 10 microg/kg/min increased cardiac contractility and protected cardiac function during endotoxemia. Neither dose interfered with the maximal contractile response to catecholamines. Type IV phosphodiesterase inhibition with Ro 20-1724 exerts beneficial effects on cardiac performance during septicemia in an in vivo animal model. Clinical studies of type IV phosphodiesterase inhibitors in critically ill patients are indicated.

Electropharmacologic effects of a new phosphodiesterase III inhibitor, toborinone (OPC-18790), assessed in an in vivo canine model

Electropharmacologic effects of a new phosphodiesterase (PDE) III inhibitor toborinone (OPC-18790) were assessed in a halothane-anesthetized, closed-chest canine model. Toborinone, 0.03 mg/kg, increased ventricular contractility, decreased total peripheral resistance, and inhibited intraventricular conduction without changing other cardiovascular parameters. A clinically relevant dose of 0.3 mg/kg increased heart rate, systolic blood pressure, and cardiac output, decreased preload to the left ventricle, enhanced atrioventricular nodal conduction, and shortened repolarization and the vulnerable period of the ventricle, in addition to enhancing the effects observed after the low dose. A high dose of 3 mg/kg of toborinone decreased systolic, mean, and diastolic pressures and prolonged the effective refractory period (ERP) in addition to the effects observed after the middle dose. No further change was detected in ventricular repolarization. Most of the cardiohemodynamic effects can be explained by the PDE III inhibition by toborinone. With regard to electrophysiologic properties, the prolongation of intraventricular conduction time and ERP by toborinone suggests sodium channel inhibition. The lack of the prolongation of ventricular repolarization suggests that previously demonstrated inhibition of I(Kr) and I(K1) and increased I(Ca-L) by toborinone might be counteracted by factors such as the cyclic AMP-dependent outward currents, I(Ks) and I(C1).

Vasorelaxant effect of a phosphodiesterase 3 inhibitor, olprinone, on isolated human radial artery

The radial artery is currently used as a viable arterial conduit for myocardial revascularization. The aims of this study were to identify phosphodiesterase 3 isoenzyme in the human radial artery isolated for coronary artery bypass grafting, and to examine the vasorelaxant effect of a cardiotonic and vasodilating phosphodiesterase 3 inhibitor, 1, 2-dihydro-6-methyl-2-oxo-5-(imidazo[1,2-a]pyridin-6-yl)-3-pyridine carbonitrile hydrochloride monohydrate (olprinone). The phosphodiesterase 3 isoenzyme was separated from the radial artery by DEAE-Sepharose chromatography. Olprinone inhibited the phosphodiesterase 3 activity with an IC(50) value of 1.25 microM. Olprinone relaxed the phenylephrine-induced contractions of endothelium-denuded arterial strips with an EC(50) value of 0. 107+/-0.029 microM (n=5). These findings indicate that the human radial artery possesses phosphodiesterase 3 isoenzyme activity and olprinone causes potent relaxation of the arterial strip in vitro through inhibition of phosphodiesterase 3 isozyme activity.

Effect of aerosolized administration of KF19514, a phosphodiesterase 4 inhibitor, on bronchial hyperresponsiveness and airway inflammation induced by antigen inhalation in guinea-pigs

BACKGROUND

Although phosphodiesterase (PDE) 3 and 4 inhibitors have received much attention for the treatment of bronchial asthma, systemic adverse effects have also been reported.

OBJECTIVE

The purpose of this study was to investigate the effect of inhaled olprinone, a newly developed PDE3 inhibitor, and KF19514, a PDE1 and 4 inhibitor, on antigen-induced airway reactions in guinea-pigs.

METHODS

Fifteen minutes after inhalation of olprinone (0.1 or 1.0 mg/mL) and KF19514 (0.1 or 0.01 mg/mL), animals were given an antigen challenge. Bronchial hyper-responsiveness and bronchoalveolar lavage fluid cell analysis were performed 24 h after the antigen challenge.

RESULTS

Inhalation of olprinone and KF19514 caused a dose-related inhibition of antigen-induced bronchoconstriction. Antigen inhalation significantly increased bronchoconstrictor responses to methacholine, and airway accumulation of neutrophils and eosinophils, 24 h after the antigen challenge. These responses were dose-dependently prevented by KF19514, but not by olprinone.

CONCLUSION

The results indicate that inhaled PDE inhibitors might be useful for treatment of bronchial asthma.

Possible mechanisms underlying the vasodilatation induced by olprinone, a phosphodiesterase III inhibitor, in rabbit coronary artery

The possible mechanisms underlying the vasodilatation induced by olprinone, a phosphodiesterase type III inhibitor, were investigated in smooth muscle of the rabbit coronary artery. Isometric force and membrane potential were measured simultaneously using endothelium-denuded smooth muscle strips. Acetylcholine (ACh, 3 microM) produced a contraction with a membrane depolarization (15. 2+/-1.1 mV). In a solution containing 5.9 mM K(+), olprinone (100 microM) hyperpolarized the resting membrane and (i) caused the absolute membrane potential level reached with ACh to be more negative (but did not reduce the delta membrane potential seen with ACh, 15.2+/-1.8 mV) and (ii) attenuated the ACh-induced contraction. In a solution containing 30 mM K(+), these effects were not seen with olprinone. Glibenclamide (10 microM) blocked the olprinone-induced membrane hyperpolarization. 4-AP (0.1 mM) significantly attenuated the olprinone-induced resting membrane hyperpolarization but TEA (1 mM) had no such effect. Glibenclamide (10 +microM), TEA (1 mM) and 4-AP (0.1 mM), given separately, all failed to modify the inhibitory actions of olprinone on (i) the absolute membrane potential level seen with ACh and (ii) the ACh-induced contraction. It is suggested that olprinone inhibits the ACh-induced contraction through an effect on the absolute level of membrane potential achieved with ACh in smooth muscle of the rabbit coronary artery. It is also suggested that glibenclamide-sensitive, ATP-sensitive K(+) channels do not play an important role in the olprinone-induced inhibition of the ACh-induced contraction.

Bronchodilator effect of inhaled olprinone, a phosphodiesterase 3 inhibitor, in asthmatic patients

The effect of topical administration of phosphodiesterase (PDE) 3 inhibitors on the airway is not clear. In order to examine the usefulness of inhaled PDE3 inhibitors in the treatment of asthma, we investigated the bronchodilator effect of inhaled olprinone, a newly developed PDE3 inhibitor, in nine asthmatic patients. On three separate study days, olprinone, salbutamol, or vehicle was administered in a double-blind and randomized fashion, and pulmonary functions were assessed over 60 min. Significant increases in FEV(1) were observed until 45 min after inhalation of olprinone without adverse cardiovascular effects. Mean maximal increases in FEV(1) were 16.0 +/- 4.0 and 20.5 +/- 4.2% with olprinone and salbutamol, respectively. The bronchodilator effect of olprinone was greater than that of salbutamol in four of the nine patients. These results suggest that the inhaled PDE3 inhibitor has a bronchodilator effect in asthmatic patients.

Effects of type IV phosphodiesterase inhibition on cardiac function in the presence and absence of catecholamines

Type IV phosphodiesterase (PDE4) inhibitors may be useful in several diseases in which catecholamine infusions are commonly used, including asthma, sepsis, and multiple organ failure. To determine whether type IV phosphodiesterase inhibitors alter baseline or catecholamine-induced changes in cardiac function or both, we examined the effects of Ro 20-1724 (PDE4 inhibitor) on several cardiac-performance parameters in the absence and presence of norepinephrine, epinephrine, isoproterenol, and dobutamine infusions (3, 1, 0.1, and 3 microg/kg/min, respectively). Male Sprague-Dawley rats received either Ro 20-1724 (10 microg/kg/min; n = 7) or vehicle (n = 6). After a left ventricular catheter was placed and connected to a heart-performance analyzer, each animal received each of the four catecholamines in randomized order (10 min per catecholamine with a 30-min washout period between infusions). In the absence of catecholamines, Ro 20-1724 significantly but mildly (i.e., <10%) increased heart rate but did not alter significantly any other measured cardiac parameter. In addition, Ro 20-1724 did not significantly alter norepinephrine-, epinephrine-, or dobutamine-induced changes in cardiac-performance parameters. There was, however, a significant attenuation of the isoproterenol-induced increase in a single measure of cardiac contractility (maximum dP/dt normalized to pressure). PDE4 inhibition does not cause significant cardiac toxicities in rats, both in the absence and presence of catecholamines. Our data suggest that PDE4 inhibitors may be safely used in critically ill patients receiving catecholamines. A clinical trial of this family of drugs in patients with critical illness is now being planned.

Vasorelaxant effect of olprinone, an inhibitor of phosphodiesterase 3, on mesenteric small artery and vein of rabbits

The effects of olprinone, a cardiotonic agent that inhibits cyclic GMP (cGMP)-inhibited phosphodiesterase, was studied on isolated rabbit mesenteric small artery and vein. In the presence of indomethacin and propranolol, olprinone at concentrations of 10 nM to 10 microM and 1 microM to 100 microM relaxed norepinephrine-stimulated mesenteric artery and vein in a concentration-dependent manner, respectively. The relaxation was not endothelium-dependent in the artery. Removal of the endothelium, however, increased marginally the response of the vein to olprinone. Olprinone-induced relaxation was less pronounced in arteries contracted with high KCl solution + norepinephrine than in those contracted with norepinephrine alone. Nicardipine inhibited this attenuating effect of high KCl solution on the olprinone-induced relaxation. Olprinone (1 microM) enhanced the relaxation of artery and vein in response to a cAMP-increasing agent, 6-(3-dimethylaminopropionyl) forskolin (NKH477), but not to a cGMP- increasing agent, glyceryl trinitrate. Norepinephrine (10 microM) and caffeine (5 mM) elicited a transient, phasic contraction of the artery in Ca2+-free solution. Both olprinone and NKH477 attenuated more potently the norepinephrine-induced contraction than the caffeine-induced contraction. When norepinephrine (10 microM) and caffeine (5 mM) were successively applied in Ca2+-free solution, the contractile effect of caffeine was diminished compared to that in artery which had not been pretreated with norepinephrine. When the contraction in response to norepinephrine was partially attenuated by 1 microM olprinone, the following contraction evoked by caffeine was enlarged. It is concluded that olprinone relaxes the small artery more strongly than the vein via its direct action on smooth muscles. It is suggested that olprinone attenuates norepinephrine-induced contraction through inhibition of receptor-operated transmembrane Ca2+ influx and Ca2+ release from intracellular storage sites.

Effect of the type IV phosphodiesterase inhibitor Ro 20-1724 on catecholamine-induced alterations in regional vascular resistance and regional blood flow

Type IV phosphodiesterase inhibitors have been studied in multiple disease processes that commonly afflict patients who are treated with catecholamine infusions. To examine whether type IV phosphodiesterases alter catecholamine-induced changes in systemic and regional hemodynamic parameters, we examined the effects of Ro 20-1724 on rats during dobutamine, epinephrine, isoproterenol, and norepinephrine infusions. Twenty-six Sprague-Dawley rats received either Ro 20-1724 or vehicle. After central and regional hemodynamic monitoring was initiated, animals received increasing doses of two of the four catecholamines. In the absence of catecholamines, Ro 20-1724 infusion caused a significant increase in heart rate and a trend toward an increase in superior mesenteric artery blood flow. Ro 20-1724 attenuated the increase in blood pressure caused by epinephrine but had no effect on the dobutamine-, isoproterenol-, or norepinephrine-induced changes in blood pressure. Ro 20-1724 had no effect on catecholamine-induced changes in renal, carotid, and hindquarter vascular resistance but did attenuate the decrease in superior mesenteric artery vascular resistance caused by isoproterenol. Type IV phosphodiesterase inhibition in combination with catecholamines has no adverse effects on regional hemodynamics; however, it can inhibit the ability of epinephrine infusion to increase blood pressure.

Comparative study of toborinone (OPC-18790) and milrinone on energy metabolism in microembolized guinea pig hearts

The effects of toborinone (OPC-18790) and milrinone on cardiac function and energetics were compared in microembolized guinea pig hearts. Male guinea pig hearts were perfused according to the Langendorff method and microembolization was induced by injecting microspheres. The hearts were then treated with toborinone (10 microM), milrinone (4 microM), and vehicle. Energy metabolism in hearts was assessed by 31-phosphorus magnetic resonance spectroscopy (31P-MRS). Microembolization produced a decrease in coronary perfusion flow (CPF), left ventricular developed pressure (LVP), and peak LVdP/dt by about 50% concomitantly with a decrease in creatine phosphate (PCr) and ATP and an increase in inorganic phosphate (Pi) and Pi/PCr ratio. Toborinone and milrinone increased peak LVdP/dt, an index of contractility, by 15 +/- 2% and 18 +/- 3%, respectively. Milrinone increased heart rate (HR) by 22 +/- 4% but toborinone did not change HR. Toborinone did not change PCr, ATP, Pi, Pi/PCr, and intracellular pH (pHi) compared with the vehicle. On the other hand, milrinone decreased PCr and increased Pi and Pi/PCr compared with toborinone or vehicle. These results suggest that the different effects between toborinone and milrinone on energy metabolism in microembolized hearts may be due to the difference of chronotropic action between these drugs. Thus toborinone, a positive inotropic agent without chronotropic action, may be effective in acute treatment of ischemic heart failure.

Cardiac and hemodynamic effects of TZC-5665, a novel pyridazinone derivative, and its metabolite in humans and dogs

1. TZC-5665 is a novel pyridazinone derivative with vasodilatory and beta-adrenergic blocking activities and type III phosphodiesterase inhibitory action. 2. In healthy volunteers, TZC-5665 was rapidly absorbed and immediately metabolized. Its main metabolite, M-2, remained at a higher concentration in plasma. Orally administered TZC-5665 reduced end-diastolic left ventricular volume (20.16 ml) and exhibited a tendency to increase ejection fraction (0.04). 3. In dogs, M-2 dose-dependently increased cardiac contractility and reduced both preload and afterload. These effects appeared more potent in the failed heart than in the normal heart. At the same dose (30 micrograms/kg), the effects of M-2 seem to be more potent than those of milrinone. 4. We concluded that TZC-5665 is a useful medication for treating patients with chronic congestive heart failure (CHF) because of the positive inotropic and vasodilating effects due to its active metabolite in addition to its own beta-adrenergic blocking actions.

OPC-18790, a novel positive inotropic agent, has both arterial and venous vascular dilating actions in the dog

OPC-18790, (+/-)6-[3-(3,4-dimethoxybenzylamino)-2- hydroxypropoxy]-2(1H)-quinolinone, is a novel positive inotropic agent with a moderate vasodilating action. We examined the vasodilating action of OPC-18790 in detail in the pentobarbital-anesthetized dogs using a colored microsphere technique for resistance vessels and a mean circulatory filling pressure method for capacitance vessels. Intravenously (i.v.) infused OPC-18790 increased the first derivative of left ventricular pressure (LVdP/dt max), cardiac output, heart rate and decreased total peripheral resistance but did not affect mean blood pressure. OPC-18790 significantly increased arterial blood flow distribution to heart and decreased vascular resistance in heart. OPC-18790 at 300 micrograms/kg i.v. and nitroglycerin at 50 micrograms/kg i.v. did not affect mean circulatory filling pressure in intact anesthetized dogs, but both compounds decreased mean circulatory filling pressure in spinally anesthetized dogs. OPC-18790 also decreased resistance to venous return but nitroglycerin did not. These results suggest that OPC-18790 has both arterial and venous vasodilating actions in addition to its positive inotropic action. These actions may produce an improvement of cardiohemodynamics in heart failure.

Effects of toborinone (OPC-18790), a new positive inotropic agent, on action potential in guinea pig sinoatrial node: compared with milrinone and E-4031

The effects of toborinone ([(+/-)-6-[3-(3,4-dimethoxybenzylamino)-2-hydroxypropoxy]-2 (1H)-quinolinone], OPC-18790), milrinone and E-4031 (1-(2-(6-methyl-2-pyridil)-1-ethyl)-4-(4-methanesulfonyl-amino-1-b enzoyl) piperidine dihydrochloride) on membrane potential were examined in isolated guinea pig sinoatrial node preparations. Toborinone, a new positive inotropic agent, prolonged cycle length (CL), depolarized maximum diastolic potential (MDP) and decreased maximum upstroke velocity (Vmax) and action potential amplitude (APA). On the other hand, milrinone, a peak III phosphodiesterase (PDE III) inhibitor, increased Vmax and APA and shortened CL and action potential duration. E-4031, an IK blocker, prolonged CL, depolarized MDP and decreased Vmax and APA. These results suggest that toborinone modulates the action potential like an IK blocker rather than a PDE III inhibitor in a sinoatrial node.

Chronic beta 1-adrenoceptor blockade sensitises the H1 and H2 receptor systems in human atrium: rôle of cyclic nucleotides

We have reported that chronic treatment of patients with beta 1-adrenoceptor blockers sensitises isolated atrial preparations to adrenaline, noradrenaline and 5-Ht. We have now examined the effect of chronic treatment with beta-adrenoceptor blockers on responses to histamine of human right atrial appendages. We compared the effects of histamine on contractile force, cyclic AMP and cyclic GMP levels as well as cyclic AMP-dependent protein kinase (PKA) activity and explored the arrhythmogenic effects of histamine in preparations obtained from patients chronically treated or not treated with beta-adrenoceptor blockers. Histamine increased contractile force in paced preparations; the effects were blocked by the H2 receptor antagonist famotidine (0.1-30 mumol/l). The maximum inotropic response to histamine was doubled and the inotropic potency of histamine 0.4 log units greater in atria from beta-adrenoceptor blocker-treated compared to non beta-adrenoceptor blocker-treated patients. Histamine elicited frequency-dependent arrhythmias that were blocked by famotidine (30 mumol/l) but not by mepyramine (1 mumol/l). The incidence of arrhythmias was higher in atria from beta-adrenoceptor blocker-treated compared to untreated patients. Histamine increased both cyclic AMP and cyclic GMP levels, as well as PKA activity, significantly more in atria from beta-adrenoceptor blocker-treated compared to those from untreated patients. Mepyramine 1 mumol/l prevented the histamine-evoked increase in cyclic GMP levels, reduced the inotropic hyperresponsiveness and abolished the hyperresponsiveness in cyclic AMP levels and PKA activity observed in patients chronically treated with beta blockers. Sodium nitroprusside 10 mumol/l caused smaller increase of cyclic GMP levels than histamine and restored the contracile force depressed by mepyramine to its original level in atria from beta-adrenoceptor blocker-treated patients. The evidence is consistent with sensitisation of both the histamine H1 and histamine H2 receptor systems by chronic beta 1-adrenoceptor blockade. H1 receptor-mediated increases in cyclic GMP, enhanced through an as yet unknown mechanism by chronic beta 1-adrenoceptor blockade, may inhibit phosphodiesterase 3 activity, thereby causing enhanced histamine-evoked increases in cyclic AMP levels and PKA activity, and accounting partially for the increased inotropic responses to histamine through H2 receptors.

Cardiovascular effects of the combination of OPC-18790 and dopamine in halothane-anesthetized dogs

OPC-18790, (+/-)-6-[3-(3,4-dimethoxybenzylamino)-2-hydroxypropoxy]-2(1H)-quin olinone, is a novel positive inotropic agent, and its mechanism of positive inotropic action involves not only phosphodiesterase inhibition, but also a prolongation of action potential duration in ventricular muscle. Prolongation of action potential duration is also a property of class III antiarrhythmic agents; therefore, we examined the cardiohemodynamic effects and arrhythmogenicity of a combination of OPC-18790 and dopamine in halothane-anesthetized dogs. Dopamine (5 micrograms/kg/min) alone increased the peak of the first derivative of left ventricular pressure (LVdP/dtmax) and cardiac output (CO) by 43-48% and 16-20%, respectively, while OPC-18790 (10 micrograms/kg/min) increased these parameters by 56% and 22%, respectively. The combination of OPC-18790 (10 micrograms/kg/min) and dopamine (5 micrograms/kg/min) and dopamine alone at an increased dose of 10 micrograms/kg/min further increased LVdP/dtmax and CO by 104-113% and 29-30%, respectively. Thus, positive inotropic effects were equally observed in both groups, and the effects of OPC-18790 and dopamine seemed to be additive. The other hemodynamic effects were similar among all groups. Arrhythmias such as premature ventricular contraction developed in 5 out of 7 dogs (71.4%) in the 10-micrograms/kg/min dopamine group, while only one premature ventricular contraction was observed in 1 of 7 dogs (14.3%) in the OPC-18790 (10 micrograms/kg/min) and dopamine (5 micrograms/kg/min) combination group. These results suggest that the combination of OPC-18790 and dopamine may provide new therapeutic options for the treatment of heart failure.

Isoenzymes of cyclic nucleotide phosphodiesterase in the human aorta: characterization and the effects of E4021

In extracts of the human aorta, five isoenzymes of cyclic nucleotide phosphodiesterase, namely, phosphodiesterase I, phosphodiesterase II, phosphodiesterase III, phosphodiesterase IV and phosphodiesterase V, were identified exclusively in the cytosolic fraction, and no phosphodiesterase activity was detected in the particulate fraction. Phosphodiesterase V and phosphodiesterase I were the major cGMP-hydrolyzing enzymes in the human aorta. A novel vasorelaxant, sodium 1-[6-chloro-4-(3,4-methylenedioxybenzyl)aminoquinazolin-2-yl ]piperidine-4- carboxylate sesquihydrate (E4021), relaxed prostaglandin F2 alpha-precontracted strips of human pulmonary artery with an ED50 value of 0.5 microM. E4021 potently and highly selectively inhibited the activity of phosphodiesterase V from human aorta with a Ki value of 2.4 nM. These results suggest that there is a unique distribution of phosphodiesterase isoenzymes in the human aorta and that inhibitors of phosphodiesterase V might be useful as a new type of vasodilator in the treatment of clinical disorders.