Osamu Kuromaru

The anti-ischemic effects of CP-060S during pacing-induced ischemia in anesthetized dogs

CP-060 S, (-)-( S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N-[2-(3 ,4-methylenedioxyphenoxy)ethyl]-amino]propyl]-1,3-thiazolidin++ +-4-one hydrogen fumarate, is a novel cardioprotective drug which prevents Na+-, Ca2+-overload and has Ca2+ channel blocking activity. We compared the anti-ischemic effects of CP-060S with those of diltiazem, a Ca2+ channel blocker, and R56865, N-[1-[4-(4-fluorophenoxy)butyl]-4-piperidinyl]-N-methyl-2-benzothiazo lamine, a Na+-, Ca2+-overload inhibitor, in a canine pacing-induced ischemia model. CP-060S 100 microg kg(-1) significantly suppressed the pacing-induced ischemic epicardial ST-segment elevation by maximally 75%, while diltiazem 100 microg kg(-1) suppressed it by maximally 35%. R56865 100 microg kg(-1) significantly suppressed the ST-segment elevation by maximally 30%. In addition, diltiazem 100 microg kg(-1) caused synergistic suppression of ST-segment elevation by 70% when administered simultaneously with R56865 100 microg kg(-1). These results suggest that a Na+-, Ca2+-overload preventive action and a Ca2+ channel blocking action independently contribute to the suppression of the ST-segment elevation. Therefore, CP-060S may suppress pacing-induced ST-segment elevation by a dual action by preventing Na+-, Ca2+-overload and the Ca2+ channel blockade.

An orally active motilin receptor antagonist, MA-2029, inhibits motilin-induced gastrointestinal motility, increase in fundic tone, and diarrhea in conscious dogs without affecting gastric emptying

The pharmacological properties of MA-2029, a selective and competitive motilin receptor antagonist, were investigated in conscious dogs after oral administration. Gastrointestinal contractile activity was recorded by chronically implanted force transducers. The proximal gastric volume was measured with a barostat under constant pressure. Gastric emptying was examined using the paracetamol absorption test. MA-2029 (0.3-10 mg/kg, p.o.) administered in the interdigestive state inhibited gastrointestinal contractions induced by motilin (3 microg/kg, i.v.) in a dose-dependent manner. MA-2029 (0.3-3 mg/kg, p.o.) also inhibited the occurrence of spontaneous phase III contractions, even though MA-2029 had no effect on basal gastrointestinal motility or basal gastric emptying even at 10 and 30 mg/kg p.o. The inhibitory effect of MA-2029 on motilin-induced gastrointestinal motility corresponded to its plasma concentration. Motilin (0.3 microg/kg/h, i.v. infusion) reduced the proximal gastric volume by about 50% of control during isobaric distension. This effect was also inhibited by MA-2029 (1-10 mg/kg, p.o.) in a dose-dependent manner. In the digestive state, injection of motilin (3 microg/kg, i.v.) induced diarrhea in 9 of 11 dogs. MA-2029 (1-30 mg/kg, p.o.) reduced the incidence of diarrhea induced by motilin in a dose-dependent manner. The results indicate that MA-2029 inhibits hypermotility induced by motilin in conscious dogs without having an effect on the basal gastrointestinal tone or gastric emptying rate. MA-2029 may be useful in treating gastrointestinal disorders in which the pathogenesis involves the elevation of circulating motilin.

Oral administration of MA-2029, a novel selective and competitive motilin receptor antagonist, inhibits motilin-induced intestinal contractions and visceral pain in rabbits

The pharmacological properties of MA-2029, a novel motilin receptor antagonist, were investigated. In vitro, MA-2029 (1 to 30 nM) competitively inhibited motilin-induced contractions in isolated rabbit duodenal longitudinal muscle strips, with a pA2 value of 9.17+/-0.01 (n=5). However, contractile responses to acetylcholine and substance P were unaffected even at 1 microM of MA-2029. MA-2029 concentration-dependently inhibited the binding of [125 I]motilin to motilin receptors in a homogenate of rabbit colon smooth muscle tissue and membranes of HEK 293 cells expressing human motilin receptors. The pKi of MA-2029 was 8.58+/-0.04 in the rabbit colon homogenate (n=4) and 8.39 in the HEK 293 cells (mean of duplicate experiments). In vivo, orally-administered MA-2029 (3 to 30 mg/kg) dose-dependently inhibited colonic contractions induced by motilin (3 microg/kg, i.v.) in conscious rabbits. Inhibition was caused by all doses at 30 min after administration and by 10 mg/kg or more at 4 h after administration. The plasma concentration of MA-2029 correlated with its inhibitory effect. Furthermore, the oral administration of MA-2029 (0.3 to 3 mg/kg) also inhibited abdominal muscle contractions (an index of the visceral pain) induced by intravenous infusion of motilin (3 microg/kg/h) during colorectal distension in conscious rabbits. These results indicate that MA-2029 is an orally active, selective and competitive motilin receptor antagonist. It is suggested that this compound may be useful for gastrointestinal disorders associated with disturbed gastrointestinal motility such as irritable bowel syndrome.

Nitrate tolerance: comparison of nicorandil, isosorbide dinitrate, and nitroglycerin in anesthetized dogs.

Development of tolerance to nicorandil (NCR), N-(2-hydroxyethyl)nicotinamide nitrate (ester), was compared with that to nitroglycerin (NTG) or isosorbide dinitrate (ISDN) in dogs. An intracoronary arterial (i.a.) injection of NCR (20 μg), ISDN (30 μg), or NTG (1 μg) caused coronary vasodilation. Development of tolerance (including cross-tolerance) was determined by examining whether the coronary vasodilating effect of i.a. injection of these drugs was attenuated by a 2-h infusion of NCR, ISDN, or NTG. The effect of i.a. injection of NCR was not affected by i.v. infusion of either NCR (10 μg/kg/min), ISDN (10 or 30 μg/kg/min), or NTG (1 or 3 μg/kg/min). The effects of i.a. injection of NTG and ISDN, however, were attenuated by the NTG or ISDN infusion, whereas they were unaffected by the NCR infusion. Additionally, the coronary vasodilating effect of NCR infusion (30 μg/kg/min, i.v.) was not attenuated by i.v. infusion of NTG (3 μg/kg/min) or ISDN (30 μg/kg/min). These results suggest that NCR does not produce tolerance, whereas NTG and ISDN do, and that there is no cross-tolerance between NCR and NTG, or ISDN in terms of the coronary vasodilating effect.

The protective effects of CP-060S on ischaemia- and reperfusion-induced arrhythmias in anaesthetized rats

CP‐060S is a novel sodium and calcium overload inhibitor, and is also characterized as a calcium channel blocker. As these activities have each been shown independently to ameliorate ischaemia damage in the myocardium, the combination may synergistically exert cardioprotection. In this study, therefore, the protective effect of CP‐060S against ischaemia‐ and reperfusion‐induced arrhythmia was evaluated in anesthetized rats. Rats were anaesthetized with pentobarbitone, and the left anterior descending coronary artery was occluded for either 5 min with subsequent reperfusion (a reperfusion‐induced arrhythmia model) or 30 min without (an ischaemia‐induced arrhythmia model). All drugs were intravenously administered 1 min before the onset of occlusion. In the reperfusion‐induced arrhythmia model, the animals in the vehicle‐treated group exhibited ventricular tachycardia (VT) in 100%, ventricular fibrillation (VF) in 89%, and death caused by sustained VF in 56%. CP‐060S (30–300 μg kg−1) dose‐dependently suppressed the incidences of arrhythmias. Significant decreases occurred at 100 μg kg−1 in VF (incidence: 42%) and mortality (8%), and at 300 μg kg−1 in VT (50%), VF (33%) and mortality (8%). This protective effect of CP‐060S was 10 times more potent than that of a pure calcium channel blocker, diltiazem (30–1000 μg kg−1) we tested, in terms of effective dose ranges. As both drugs decreased myocardial oxygen consumption estimated by rate‐pressure product to a similar extent, the calcium channel blocking activity of CP‐060S would not seem to be sufficient to explain its potency. In the same model, co‐administration of ineffective doses of diltiazem (300 μg kg−1) and a sodium and calcium overload inhibitor, R56865 (100 μg kg−1), produced significant suppression of VT (incidence: 62%), VF (46%) and mortality (8%). By contrast, co‐administration of R56865 at the same dose with CP‐060S (300 μg kg−1) did not add to the effect of a single treatment of CP‐060S. In the ischaemia‐induced arrhythmia model, CP‐060S (300 μg kg−1) significantly decreased the incidence of VF from 75% to 29%, whereas diltiazem (1 mg kg−1) was ineffective. These results suggest that CP‐060S inhibits both ischaemia‐ and reperfusion‐induced arrhythmia. The combination of the calcium channel blocking effect and the calcium overload inhibition was hypothesized to contribute to these potently protective effects.

CARDIOVASCULAR EFFECTS OF ISOSORBIDE DINITRATE INFUSED INTRAVENOUSLY INTO ANAESTHETIZED DOGS

1. The cardiohaemodynamic response and the development of tolerance to isosorbide dinitrate (ISDN) were examined in anaesthetized, open‐chest dogs.

Effects of CP‐060S, a novel cardioprotective drug, in the methacholine‐induced ECG change model in rats

We compared the antianginal effect of CP‐060S, a novel cardioprotective drug with Na+ and Ca2+ overload‐preventing activity as well as Ca2+ channel antagonistic activity, with that of diltiazem, in an experimental model of vasospastic angina induced by methacholine in anaesthetized rats. Intra‐aortic injection of methacholine at the coronary ostium provoked the ST‐segment elevation of the electrocardiogram (ECG), indicating myocardial ischemia. CP‐060S (3, 5 and 10 mg/kg, i.d.) significantly and dose‐dependently suppressed the methacholine‐induced ST‐elevation, with the duration of action being at least 3 h at the highest dose. In addition, CP‐060S at 3 mg/kg could inhibit the ST‐elevation without producing significant changes in blood pressure, heart rate or rate‐pressure product (RPP). In contrast, diltiazem (10 and 30 mg/kg, i.d.) significantly decreased the RPP, a significant suppression of the ST‐elevation could only be achieved at the highest dose and its duration of action was about 2 h. Similar results were obtained with i.v. administration of the drugs, i.e. CP‐060S given i.v. could inhibit the ST‐elevation with less haemodynamic changes than diltiazem. In conclusion, CP‐060S exerted a more potent and sustained protection against myocardial ischemia evoked by methacholine than diltiazem. The characteristics of the effects of CP‐060S observed here suggest that this drug may be a desirable drug for the treatment of vasospastic angina.

Effects of nicorandil and verapamil, antianginal agents, on plasma digoxin concentrations in rats and dogs

The effects of equihypotensive doses of nicorandil and verapamil on plasma digoxin concentrations have been assessed in rats and dogs. In a single digoxin dose study, digoxin (1 mg kg−1) alone, or in combination with nicorandil (5 mg kg−1) or verapamil (25 mg kg−1) was given orally to rats. When given chronically to rats, a single dose of digoxin (1 mg kg−1) orally for 7 consecutive days was followed, on day 8, by digoxin alone, or together with nicorandil (5 mg kg−1) or verapamil (25 mg kg−1). In dogs, a loading dose of digoxin (50 μg kg−1) was given orally on day 1, then 25 μg kg−1 was administered for the following 6 days. On day 8, digoxin (50 μg kg−1) was given with nicorandil (5 mg kg−1) or verapamil (20 mg kg−1). In rats, the AUC0–24 and Cmax of plasma digoxin were enhanced significantly by coadministration of verapamil, but not by nicorandil. In dogs, verapamil significantly increased the Cmax of plasma digoxin, but not the AUC. Nicorandil had no effect on either parameter.