Michiaki Tominaga

Characterization of a novel aquaretic agent, OPC‐31260, as an orally effective, nonpeptide vasopressin V2 receptor antagonist

1 OPC‐31260, a benzazepine derivative, has been studied for its ability to antagonize the binding of arginine vasopressin (AVP) to receptors in rat liver (V1) and kidney (V2) plasma membranes, for antagonism of the antidiuretic action of AVP in alcohol‐anaesthetized rats and for diuretic action in conscious normal rats. 2 OPC‐31260 caused a competitive displacement of [3H]‐AVP binding to both V1 and V2 receptors with IC50 values of 1.2 ± 0.2 × 10−6 m and 1.4 ± 0.2 × 10−8 m, respectively. 3 OPC‐31260 at doses of 10 to 100 μg kg−1, i.v., inhibited the antidiuretic action of exogenously administered AVP in water‐loaded, alcohol‐anaesthetized rats in a dose‐dependent manner. OPC‐31260 did not exert an antidiuretic activity suggesting that it is not a partial V2 receptor agonist. 4 After oral administration at doses of 1 to 30 mg kg−1 in normal conscious rats, OPC‐31260 dose‐dependently increased urine flow and decreased urine osmolality. The diuretic action of OPC‐31260 was characterized as aquaresis, the mode of diuretic action being different from previously known diuretic agents such as furosemide, hydrochlorothiazide and spironolactone. 5 The results indicate that OPC‐31260 is a selective V2 receptor antagonist and behaves as an aquaretic agent. OPC‐31260 will be a useful tool in studying the physiological role of AVP and in the treatment of various conditions characterized by water retention.

7-Chloro-5-hydroxy-1-[2-methyl-4-(2-methylbenzoyl-amino)benzoyl ]-2,3,4,5-tetrahydro-1H-1-benzazepine (OPC-41061): a potent, orally active nonpeptide arginine vasopressin V2 receptor antagonist.

We previously reported a series of benzazepine derivatives as orally active nonpeptide arginine vasopressin (AVP) V2 receptor antagonists. After the lead structure OPC-31260 was structurally evaluated and optimized, the introduction of the 7-Cl moiety on the benzazepine and 2-CH3 on the aminobenzoyl moiety enhanced its oral activity. The new AVP-V2 selective antagonist OPC-41061 was determined to be a potent and orally active agent.

OPC-21268, a vasopressin V1 antagonist, produces hypotension in spontaneously hypertensive rats.

We studied the hypotensive effects of OPC-21268, an orally effective nonpeptide vasopressin V1 receptor antagonist, in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP). OPC-21268 was given intravenously to conscious, freely moving SHR and SHRSP. We used young and aged animals to examine the contribution of vasopressin to the development and maintenance of hypertension in both types of rats. In SHR, hypertension was fully established at 38 weeks of age, and intravenous injection of OPC-21268 produced slight hypotensive effects at either 38 or 70 weeks of age. In SHRSP, hypertension developed at 25 weeks of age, and blood pressure was sustained at a high level (approximately 250 mm Hg systolic blood pressure) thereafter. Intravenous administration of OPC-21268 did not cause hypotensive effects in young rats at 15 weeks, but at 25 weeks a significant decrease in blood pressure was observed. Furthermore, in the malignant state of SHRSP (35 to 41 weeks), OPC-21268 significantly decreased mean blood pressure by 32.4 +/- 7.9 mm Hg (mean +/- SEM) at 3 mg/kg IV, and the decrease was dose dependent (0.3 to 3.0 mg/kg). Plasma vasopressin concentrations were increased in a more malignant phase of SHRSP at 45 weeks of age, whereas at other ages of SHRSP or in SHR, plasma vasopressin levels were not increased. These results suggest that vasopressin plays an important role through V1 receptors in the maintenance of hypertension, at least in the malignant phase of SHRSP, and OPC-21268 may be therapeutically useful in the treatment of some types of hypertension.

Cardiovascular actions of OPC-18790: A novel positive inotropic agent with little chronotropic action

SummaryOPC-18790 [(±)-6-[3-(3,4-dimethoxy-benzylamino)- 2 - hydroxypropoxy] - 2(1H) - quinolinone], a novel positive inotropic agent, was investigated in several in vitro and in vivo experiments to elucidate its cardiovascular effects and its mechanism of action. In isolated blood-perfused dog heart preparations, OPC-18790 increased contractile force at 10 to 1,000 nmol i.a.; increased coronary arterial blood flow at 30 to 1,000 nmol; and deceased sinus rate slightly at 1,000 nmol. Atrio-ventricular nodal conduction was slightly facilitated with OPC-18790 (10 to 1,000 nmol), whereas ventricular automaticity tended to decrease. OPC-18790 (10−6 to 10−4 M) increased contractile force in isolated ventricular muscles of dogs, cats, rabbits and guinea pigs but not rats. OPC-18790 increased left ventricular contractile force dosedependently in anesthetized open-chest dogs and in conscious dogs with slight or no changes in heart rate and blood pressure. The positive inotropic effect of OPC-18790 was not affected by β-blockade. OPC-18790 (10−5 to 10−4 M) prolonged the duration of action potential in guinea pig papillary muscles. Na+, K+-ATPase was not inhibited, but peak-III phosphodiesterase (low Km cyclic AMP specific fraction, inhibited by cyclic GMP) was inhibited by OPC-18790 (IC50 = 0.41 × 10−6 M) in dog myocardium. However, such an inhibitory action of phosphodiesterase can hardly be reconciled with the lack of a positive chronotropic effect shown by OPC-18790. Thus, these results suggest that OPC-18790 may have an additional mechanism. The cardiovascular effects revealed by this study suggest that OPC-18790 may exert a beneficial effect in the treatment of congestive heart failure.

Characterization of a novel nonpeptide vasopressin V2‐agonist, OPC‐51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine‐vasopressin (AVP) V2‐receptor agonist, OPC‐51803. Pharmacological properties of OPC‐51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V2, V1a and V1b) and compared with those of 1‐desamino‐8‐D‐arginine vasopressin (dDAVP), a peptide V2‐receptor agonist. OPC‐51803 and dDAVP displaced [3H]‐AVP binding to human V2‐ and V1a‐receptors with Ki values of 91.9±10.8 nM (n=6) and 3.12±0.38 nM (n=6) for V2‐receptors, and 819±39 nM (n=6) and 41.5±9.9 nM (n=6) for V1a‐receptors, indicating that OPC‐51803 was about nine times more selective for V2‐receptors, similar to the selectivity of dDAVP. OPC‐51803 scarcely displaced [3H]‐AVP binding to human V1b‐receptors even at 10−4 M, while dDAVP showed potent affinity to human V1b‐receptors with the Ki value of 13.7±3.2 nM (n=4). OPC‐51803 concentration‐dependently increased cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP) production in HeLa cells expressing human V2‐receptors with an EC50 value of 189±14 nM (n=6). The concentration‐response curve for cyclic AMP production induced by OPC‐51803 was shifted to the right in the presence of a V2‐antagonist, OPC‐31260. At 10−5 M, OPC‐51803 did not increase the intracellular Ca2+ concentration ([Ca2+]i) in HeLa cells expressing human V1a‐receptors. On the other hand, dDAVP increased [Ca2+]i in HeLa cells expressing human V1a‐ and V1b‐receptors in a concentration‐dependent fashion. From these results, OPC‐51803 has been confirmed to be the first nonpeptide agonist for human AVP V2‐receptors without agonistic activities for V1a‐ and V1b‐receptors. OPC‐51803 may be useful for the treatment of AVP‐deficient pathophysiological states and as a tool for AVP researches.

Effects of OPC-18790, a new positive inotropic agent, on energetics in the ischaemic canine heart : a 31P-MRS study

OBJECTIVE Effects of OPC-18790, a novel positive inotropic agent, on cardiohaemodynamics and cardiac energetics were assessed simultaneously in dogs with cardiac ischaemia using phosphorus-31 magnetic resonance spectroscopy (31P-MRS) and compared with those of amrinone, a pure cGMP-inhibited PDE inhibitor. METHODS Cardiac ischaemia was produced by partial stenosis of the coronary artery. Dogs with cardiac ischaemia were instrumented for the determination of regional coronary blood flow (non-radioactive coloured microsphere method), regional contractile function (sonomicrometry), and haemodynamics. Myocardial phosphate compounds were measured simultaneously by 31P-MRS. RESULTS Coronary stenosis produced regional dyskinesis, a slight decrease in cardiac output (CO), intracellular acidosis, an increase in the inorganic phosphate (Pi)/creatine phosphate (PCr) ratio concomitantly with a decrease in regional coronary blood flow (CBF) in the ischaemic region. OPC-18790 dose-dependently produced an increase in contractility (measured by peak LVdP/dt) and CO, with only slight changes in heart rate (HR) and mean blood pressure (mBP). OPC-18790 did not change regional dyskinesis, but improved the Pi/PCr ratio at the high dose compared with ischaemic values (before drug administration). Amrinone produced an increase in CO comparable to that of OPC-18790; however, the increase in peak LVdP/dt was smaller while the increase in HR and decrease in mBP were larger than those seen with OPC-18790. Amrinone worsened the Pi/PCr ratio and intracellular acidosis only at the high dose. CONCLUSION These observed differences in energy metabolism between OPC-18790 and amrinone at the high dose may be due to the ability of OPC-18790 to increase CBF in the ischaemic region and which may attributed to its differing effect on overall haemodynamics. Thus, OPC-18790 may be useful in the management of ischaemic heart failure.

Metabolism of a New Positive Inotropic Agent, 3,4-Dihydro-6-[4-(3,4-Dimethoxybenzoyl)-1-Piperazinyl]-2(1H)-Quinolinone (Opc-8212) in the Rat, Mouse, Dog, Monkey and Human

1. After OPC-8212 was orally given to rats, mice, dogs, monkeys and humans, its metabolites were identified by n.m.r. and mass spectrometry, and their concentrations in the plasma, urine and faeces of these species were measured by high-performance liquid chromatography (h.p.l.c.). 2. Hydrolysis of the amide group, oxidation and cleavage of the piperazine ring, O-demethylation of the methoxy group, and conjugation were proposed as metabolic pathways of OPC-8212. 3. In rats, mice and monkeys given OPC-8212 orally, metabolites M-1 to M-6 were detected in the plasma, urine and faeces, while M-1, -4, -5 and M-6 were detected in dogs, and M-1, M-3, M-4, M-5 and M-6 were detected in humans. 4. Conjugates of metabolites M-6 and M-7, with glucuronic acid and sulphuric acid, were observed in the urine of rats and humans.

Differential effects of OPC‐18790, amrinone and dobutamine on cardiac function and energy metabolism in the guinea‐pig isolated ischaemic heart

1 The effects of OPC‐18790, a novel positive inotropic agent, on cardiac function and myocardial energy metabolism in the guinea‐pig isolated heart with ischaemia were studied by 31P‐magnetic resonance spectroscopy (MRS) and compared with those of amrinone and dobutamine. 2 Cardiac ischaemia was induced by intracoronary infusion of 15 μm microspheres to reduce coronary perfusion flow (CPF) by 50%. Microsphere embolisation caused a 40% decrease in left ventricular systolic pressure (LVSP), cardiac contractility measured by peak of ventricular pressure development (LVdP/dt) and slightly reduced heart rate. There was also a decrease in ATP and creatine phosphate (PCr) by 20%, an increase in inorganic phosphate (Pi) by 25% and an acidic shift of intracellular pH in the ischaemic heart. 3 In the ischaemic heart, OPC‐18790, amrinone and dobutamine were applied at concentrations which increased LVdP/dt by about 60%. These compounds increased LVP by 15% to 30% and increased CPF by about 10%. Amrinone and dobutamine but not OPC‐18790 increased heart rate. When these drugs produced the haemodynamic changes described above, amrinone and dobutamine reduced ATP and PCr, increased Pi and produced further intracellular acidosis, whereas, OPC‐18790 did not change these parameters. 4 Cardiac pacing at 285 beats min−1 produced decreases in LVP, LVdP/dt and CPF by about 30%, 20%, 5%, respectively and an increase in Pi, decreases in PCr and ATP, and intracellular acidosis. 5 These results suggest that degradation of high energy phosphate compounds closely relates to increase in heart rate in the ischaemic heart. Positive inotropic agents without chronotropic action seem to be beneficial in support of the ischaemic heart.

EFFECTS OF VASODILATORS ON THE SIGNAL INTENSITY OF PERFLUOROCARBON MONITORED BY IN VIVO 19F-NMR SPECTROSCOPY

The effects of vasodilators on peripheral vessels were examined by monitoring the 19F-NMR signal of perfluorocarbon in vivo. Nitroglycerin, a venodilator that acts mainly on venous smooth muscle, increased the signal intensity of FC-43, whereas hydralazine, a typical arteriolar dilator that acts on arteriolar smooth muscle, decreased the signal intensity. These results indicate that the in vivo effects of vasodilators on smooth muscles of the venous and arterial systems are reflected by their effects on the signal intensity of FC-43.

Venodilatory effect of pranidipine, a calcium channel blocker, monitored with perfluorocarbon in vivo 19F-NMR spectroscopy

We previously reported that the (19)F-NMR signal intensity of perfluorocarbon was increased by a venodilator, nitroglycerine, and decreased by an arteriodilator, hydralazine. In the present study, we demonstrated that pranidipine, a calcium channel blocker, increased the intensity of the FC-43 signal, while nifedipine, a prototype of calcium channel blockers, did not. These results suggest that pranidipine dilates the venous system in contrast to nifedipine.