Synthesis and antiarrhythmic activity of cis-2,6-dimethyl-alpha,alpha-diaryl-1-piperidinebutanols.

A series of alpha,alpha-diaryl-1-piperidinebutanols was evaluated for antiarrhythmic activity in the coronary ligated dog model. Structure-activity relationship studies indicated that the 2,6-dimethylpiperidine group yielded compounds with the best antiarrhythmic profiles in this series. The length of the methylene chain separating the diarylcarbinol and the amino group was not crucial. Substitution of a hydrogen or a number of functional groups for the hydroxyl group had little effect on efficacy or duration but yielded compounds that produced severe tachycardias. Replacement of one of the aryl groups by hydrogen or a pyridinyl or cyclohexyl group had little effect on efficacy but decreased the duration of action. Compound 18 (pirmenol) was ultimately chosen for further studies and is now being investigated in man.

Synthesis and antiarrhythmic activity of alpha-[(diarylmethoxy)methyl]-1-piperidineethanols.

A series of alpha-[(diarylmethoxy)methyl]-1-piperidineethanols was evaluated for antiarrhythmic activity in the coronary artery ligated dog model. Structure-activity relationship studies indicated that the 2,6-dimethylpiperidine group afforded the best antiarrhythmic agents in this series and was essential for long duration of action. This investigation indicated that quaternary ammonium salts were not essential for a long duration of action. It was also shown that the antiarrhythmic activity could be separated from the tachycardia frequently caused by this type of agent.

Ribose-modified adenosine analogues as adenosine receptor agonists.

Analogues of the potent adenosine receptor agonist (R)-N-(1-methyl-2-phenylethyl)adenosine (R-PIA), modified at N9, were prepared and evaluated for adenosine A1 and A2 receptor binding and in vivo central nervous system and cardiovascular effects. The modifications at N9 include deoxy sugars, 5'-substituted-5'-deoxyriboses, non-ribose sugars, sugar ring homologues, and acyclic sugar analogues. Most of the derivatives have poor affinity for adenosine receptors. Only minor modifications at C5' and C3' maintain potent binding. In general, those derivatives exhibiting in vivo behavioral or cardiovascular effects also have the highest affinity for adenosine receptors.

Rational design, synthesis, and biological activity of benzoxazinones as novel factor Xa inhibitors.

Inappropriate thrombus formation within blood vessels is the leading cause of mortality in the industrialized world. Factor Xa (FXa) is a trypsin-like serine protease that plays a key role in the blood coagulation cascade and represents an attractive target for anticoagulant drug development. From a high-throughput in vitro mass screen of our chemical library, we identified 4-[5-[(2R,6S)-2, 6-dimethyltetrahydro-1(2H)-pyridinyl]pentyl]-2-phenyl-2H-1, 4-benzoxazin-3(4H)-one (1a) as an inhibitor of FXa with an IC(50) of 27 microM. Through a combination of SAR studies and molecular modeling, we synthesized 3-(4-[5-[(2R,6S)-2, 6-dimethyltetrahydro-1(2H)-pyridinyl]pentyl]-3-oxo-3,4-dihydro-2H- 1,4-benzoxazin-2-yl)-1-benzenecarboximidamide (1n) which was a potent FXa inhibitor with an IC(50) of 3 nM. This compound exhibited high selectivity for FXa over other related serine proteases and was efficacious when dosed intravenously in rabbit and dog antithrombotic models.

Preclinical pharmacology of pirmenol.

Pirmenol, a novel pyridinemethanol derivative, is active in a variety of experimental arrhythmic models of diverse etiology and has a favorable therapeutic index compared with other class I agents. Animal pharmacology studies showed that pirmenol is highly efficacious whether the arrhythmias were atrial or ventricular in origin, chemically, mechanically or electrically induced or of the automaticity or reentrant types. The conscious coronary artery-ligated (Harris) dog model best allowed simulation of a variety of clinical situations in which pirmenol could be used either alone or in combination. Pirmenol was highly effective by both the intravenous and oral routes, causing immediate suppression, prevention or termination of cardiac arrhythmias. Preclinical studies in the dog showed an excellent correlation between the dose of pirmenol, plasma levels and antiarrhythmic efficacy. Administration of pirmenol in the dog at intentionally accelerated infusion rates suggested a relatively wide margin of safety for pirmenol compared with other class I agents. Analysis of the pharmacokinetic data led to the modeling of a rapid infusion-slow infusion bolus for sustained intravenous administration, thereby optimizing therapeutic utility. In vitro electrophysiologic studies in dog Purkinje fibers revealed possibly unique differences of pirmenol from other antiarrhythmic agents. It depresses fast and slow response automaticity and its electrophysiologic effects were less variable than other class I drugs over a spectrum of potassium levels. To test the relevance of the in vitro electrophysiologic results, pirmenol's antiarrhythmic efficacy was assessed in several in vivo dog models in which serum potassium was either increased or decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

The antithrombotic effects of CI-1031 (ZK-807834) and enoxaparin in a canine electrolytic injury model of arterial and venous thrombosis.

Factor Xa is a serine protease positioned at the convergence point of the intrinsic and extrinsic coagulation pathways and is therefore an attractive target in the development of novel anticoagulant drugs. The objective of this study was to evaluate the efficacy of CI-1031 (N-[2-[5-amidino-2-hydroxyphenoxy]-6-[3-(1-methyl-1H-imidazolin-2-yl)-phenoxy]-3,5-difluoropyrid), a potent and selective inhibitor of Factor Xa, in a canine electrolytic injury model of arterial and venous thrombosis. Enoxaparin (enoxaparin sodium), a low molecular weight heparin currently approved for treatment and prevention of deep vein thrombosis and unstable angina, was also tested for efficacy in this model. CI-1031 was administered intravenously to anesthetized dogs at three doses: 1.25, 2.5 and 5 microg/kg/min (n=5 for each group) as a continuous infusion for 5.5 h. The control group (n=5) received a continuous infusion of vehicle (3.69 mmol citric acid and 0.9% sodium chloride solution) at a rate of 1 ml/kg/h. Ninety minutes after administration of CI-1031 prothrombin times increased 1.2-, 1.6- and 2.0-fold over baseline values in the 1.25, 2.5 and 5 microg/kg/min groups, respectively. The time to formation of an occlusive thrombus in the femoral arteries averaged 69+/-5 min in the control group compared to 127+/-19, 192+/-33 and 219+/-15 min in the low-, mid- and high-dose CI-1031 groups. In the femoral veins, occlusion time in the controls averaged 56+/-11 min compared to 153+/-22, 137+/-30 and 214+/-26 min in the three treatment groups. Thrombus weights in the control arteries averaged 51+/-4 mg compared to 45+/-5, 28+/-10 and 15+/-3 mg in the CI-1031 treated groups. On the venous side, control thrombus weights averaged 96+/-18 mg compared to 75+/-16, 51+/-16 and 25+/-4 mg in the low-, mid- and high-dose CI-1031 groups. A plasma CI-1031 concentration of approximately 400 ng/ml was associated with a 50% reduction in thrombus weight relative to control animals. Enoxaparin was administered intravenously at a loading dose of 50, 100 or 200 IU/kg for 1 h followed by a maintenance infusion of 25, 50 or 100 IU/kg/h for 4.5 h. The most dramatic changes in coagulation parameters were observed in thrombin time with virtually no changes in prothrombin time. Enoxaparin elicited a dose-dependent increase in time to thrombotic occlusion and a dose-dependent decrease in thrombus weight similar to that observed with CI-1031. Time to occlusion in the enoxaparin-treated groups averaged 117+/-33, 188+/-32 and 217+/-22 min in the low-, mid- and high-dose groups in the femoral arteries and 84+/-22, 171+/-31 and 133+/-33 min in the femoral veins. Thrombus weights averaged 33+/-10, 12+/-5 and 10+/-4 mg in the arteries and 32+/-9, 13+/-2 and 21+/-6 mg in the veins in the low-, mid- and high-dose groups. Blood loss with CI-1031 tended to be less than enoxaparin at doses that provided comparable efficacy. These results demonstrate that CI-1031, like enoxaparin, is an effective antithrombotic agent in an established canine model of arterial and venous thrombosis. CI-1031 provided dose-dependent efficacy with minimal changes in ex vivo coagulation parameters, suggesting it may be a safe and effective antithrombotic agent for both arterial and venous indications.

A novel model of venous thrombosis in the vena cava of rabbits.

The objective of this study was to develop and validate a new experimental model of venous thrombosis in the rabbit. A 3-cm length of siliconized PE tubing was used as a veno-venous shunt inserted into the abdominal vena cava of anesthetized rabbits. The PE tubing contained six cotton threads which helped to restrict blood flow through the tubing and served as a foreign, thrombogenic surface upon which a thrombus could develop. By continuously measuring blood flow through the vena cava, the rate of thrombus development can be monitored until zero flow is achieved indicating that a completely occlusive thrombus is present. The shunt can be removed making it possible to weigh the thrombus and/or determine its composition. A second shunt can be placed in the vena cava to make a second determination of time to occlusion and thrombus weight, using the data from the first shunt as an internal control standard for comparison. Reproducibility of the technique was demonstrated in a control group (n = 7) in which two successive shunts were used without an antithrombotic intervention. In studies with the first and second shunts, time to occlusion averaged 20.6+/-5.2 min and 20.2+/-5.7 min (pNS), respectively. The net thrombus weights (less the wet weight of the cotton threads) were 49.0+/-3.5 mg and 47.0+/-3.3 mg (pNS). Histologic examination of the thrombi indicated that they were largely composed of fibrin and red blood cells, consistent with the characteristics of venous thrombi. The low molecular weight heparin (LMWH) enoxaparin was used as an antithrombotic intervention to validate the model. Dose-dependent changes in time to occlusion and thrombus weight were achieved which paralleled alterations in coagulation parameters (thrombin time and activated partial thromboplastin time) and bleeding time determined with an ear bleeding technique. The veno-venous shunt model is easy to use, reproducible, and responds appropriately to an antithrombotic intervention, indicating that it should be useful for experimental evaluation of antithrombotic agents designed for venous thromboembolic disorders.

Pharmacokinetics and pharmacodynamics of pirmenol enantiomers in coronary artery ligated dogs.

The pharmacokinetics and pharmacodynamics of pirmenol enantiomers were investigated in coronary artery ligated mongrel dogs. Reduction in frequency of premature ventricular complexes (PVCs) was determined following intravenous administration of 5-mg/kg doses of racemic pirmenol (n = 5), (+)-pirmenol (n = 4), and (-)-pirmenol (n = 4), each given as a 5-min infusion. Electrocardiographic signals and blood samples were obtained serially over a 4-h period. Pirmenol enantiomer concentrations in plasma were determined by a stereospecific assay. Following the racemate dose, (-)-pirmenol had 47% lower clearance and 33% lower steady-state distribution volume than (+)-pirmenol. These differences could be mostly explained by stereoselective plasma protein binding, reflected in a 58% higher unbound fraction for (+)-pirmenol compared with (-)-pirmenol following racemate administration. Unbound pirmenol distribution volumes were nearly identical for both enantiomers, and unbound clearance was only 16% lower for (-)-pirmenol than (+)-pirmenol following administration of the racemate. Similar trends were observed for pirmenol enantiomers administered individually. Both pirmenol enantiomers were equally effective in arrhythmia suppression. The antiarrhythmic response of coronary artery ligated dogs to pirmenol was described by a sigmoid Emax model, and no statistically significant differences were observed in the pharmacodynamic parameters [i.e., EC50 (plasma concentration at 50% of maximum drug effect), S (constant that reflects the sigmoidal shape of the effect-concentration curve), and EC90 (plasma concentration at 90% of maximum drug effect)] for (+)-pirmenol, (-)-pirmenol, or pirmenol racemate.

Pirmenol: preclinical pharmacology.

Pirmenol, a novel pyridinemethanol derivative, is active in a variety of experimental arrhythmic models of diverse etiology. Animal pharmacology studies showed that pirmenol is highly efficacious whether the arrhythmias were atrial or ventricular in origin; chemically, mechanically, or electrically induced; or of the automaticity or reentrant types. The conscious coronary artery-ligated (Harris) dog model best allowed simulation of a variety of clinical situations in which pirmenol could be used either alone or in combination. Pirmenol was highly effective by both the intravenous and oral routes, causing immediate suppression, prevention, or termination of cardiac arrhythmias. Preclinical studies in the dog showed an excellent correlation between the dose of pirmenol, plasma levels, and antiarrhythmic efficacy. Administration of pirmenol in the dog at intentionally accelerated infusion rates suggested a relatively wide margin of safety for pirmenol compared with other class I agents. In vitro electrophysiologic studies in dog Purkinje fibers revealed possibly unique differences of pirmenol from other antiarrhythmic agents. It depresses fast and slow response automaticity and its electrophysiologic effects were less variable than other class I drugs over a spectrum of potassium levels. To test the relevance of the in vitro electrophysiologic results, pirmenol's antiarrhythmic efficacy was assessed in several in vivo dog models in which serum potassium was either increased or decreased. Studies comparing pirmenol and disopyramide clearly showed a relative lack of serum potassium dependence for pirmenol, suggesting a potential clinical advantage over disopyramide and other antiarrhythmics in variable potassium settings. The clinical relevance of these observations will have to be established in patients with variable potassium levels. Overall, pirmenol compared favorably with other reference agents in efficacy and safety in extensive preclinical investigations.

Pirmenol hydrochloride (CI-845): antiarrhythmic profile in coronary artery ligated conscious dogs.

The antiarrhythmic profile of CI-845 (pirmenol hydrochloride) was assessed in conscious, coronary artery ligated dogs. In single-dose studies in these arrhythmic dogs, CI-845 administered by the intravenous, intranuscular, and oral routes was highly effective in restoring normal sinus rhythm. A 2.5 mg/kg dose was effective against the arrhythmias occurring on the second day after ligation, while 5 mg/kg was effective against the higher-rate arhythmias of the first day after ligation. The reference agents ajmaline, aprindine, disopyramide, lidocaine, mexiletine, procainamide, and quinidine were also tested, and in this model, CI-845 had greater efficacy, a longer duration of activity, and/or a wider safety margin. In slow rate intravenous infusion studies, 1-2 mg/kg/hr of CI-845 maintained near total arrhythmia conversion in first-day postligation dogs. Rapid rate intravenous infusion studies (10 mg/kg/hr) demonstrated a good correlation between the CI-845 dose, plasma level, and arrhythmia conversion, as well as a wide margin of safety. Mean conversions to 80% normal rhythm were achieved at 2.5 mg/kg, with associated plasma levels of 0.8 +/- 0.1 micron/ml, while first sings or gross toxicity occurred at 21.7 +/- 2.4 mg/kg at plasma levels of 6.2 +/- 0.4 micron/ml. There were minimal effects on cardiac conduction and blood pressure even at large doses. In drug interaction studies, CI-845 was safe and effective in combination with disopyramide, lidocaine, procainamide, propranolol, and quinidine. The results clearly show CI-845 to be an orally effective, long-acting antiarrhythmic agent with a favorable margin of safety in the coronary artery ligated dog model.

Pirmenol hydrochloride (CI-845) and reference antiarrhythmic agents: effects on early ventricular arrhythmias after acute coronary artery ligation in anesthetized rats.

The coronary artery-ligated rat was investigated as an experimental model for studying the effects of pirmenol hydrochloride and reference for studying the effects of pirmenol hydrochloride and reference agents on early ventricular arrhythmias. Coronary artery ligation caused 89% lethality (ventricular fibrillation) within 10 min in untreated control rats. Vagal stimulation applied during periods of high-rate ventricular tachycardia reduced sinus, atrioventricular nodal and ventricular ectopic beats, with no uncoupled ectopic beats seen during stimulation. Rats studied with composite epicardial electrodes showed continuous electrical activity throughout diastole. These factors indicate that a reentry mechanism is likely involved. Pretreatment with pirmenol afforded protection in a dose-related fashion. A dose of 1.25 mg/kg increased survival to 58%, and all rats dosed with 2.5 to 10 mg/kg survived. Suppression of ventricular fibrillation was dose related and was complete at 5 mg/kg. The pirmenol plasma levels of 1.2 +/- 0.1 microgram/ml seen after the 5 mg/kg dose are similar to plasma levels seen at clinically effective doses, as well as at doses effective in other experimental arrhythmias. The reference agent quinidine was also highly effective in this model, all rats pretreated with 5 mg/kg survived with reduced premature ventricular beats and without a single episode of ventricular fibrillation or death. Fibrillation and/or death were also reduced by the reference agents, bretylium, lidocaine, propranolol and verapamil. The high efficacy of pirmenol against early ventricular arrhythmias in this study further defines its spectrum of activity, and suggests that pirmenol may be effective in a clinical setting where a reentrant mechanism is operative.

Blood pressure and heart rate effects of alkyl ether phospholipids in conscious renal, spontaneously hypertensive, and normotensive rats.

The blood pressure and heart rate effects of a synthetic alkyl ether phospholipid and similar lipids derived from beef heart and egg yolk were studied in normotensive, renal, and spontaneously hypertensive rats. Each agent (1.25 to 10 micrograms/kg) produced a dose-related decrease in blood pressure and increase in heart rate in each model after rapid IV injection. The degree of blood pressure lowering was dependent upon the pretreatment blood pressure. Alkyl ether phospholipid was infused at 10 to 30 micrograms/kg/min to SHR and to platelet depleted SHR; comparable effects (blood pressure decreases and heart rate increases) were noted in both models. Reversal of the epinephrine pressor response was seen in all rats. When administered orally in ascending doses on three consecutive days, 50 and 150 micrograms/kg b.i.d. doses (Day 1 and 2) were inactive whereas 500 micrograms/kg b.i.d. (Day 3) decreased blood pressure by 25 +/- 8 and 21 +/- 8 mm Hg in renal and spontaneously hypertensive rats, respectively. Side effects (by all routes) included limp, cyanotic hind limbs and sedation and were similar in SHR and platelet depleted SHR. Significant, sustained blood pressure lowering was not achieved by any of the alkyl ether phospholipids in the conscious rat models at doses devoid of limiting side effects. The results of these studies show: 1) the BP, HR, and toxic profiles of all three alkyl ether phospholipids were qualitatively similar, 2) at doses causing significant BP lowering there was epinephrine reversal suggesting an alpha-adrenergic blocking component of action, 3) the BP, HR, and toxic effect profiles of alkyl ether phospholipid were comparable in normal and platelet depleted SHR and apparently not platelet-dependent, 4) sustained antihypertensive activity could be achieved by the oral route; however the effects were modest (12 +/- 4% decrease) and associated with limiting side effects.

Effect of adenosine deaminase inhibition with pentostatin on myocardial stunning in dogs.

Pentostatin (2-deoxycoformycin) is a potent inhibitor of adenosine deaminase and has been demonstrated to augment endogenous adenosine levels during regional and global myocardial ischemia. Based on the rationale that increasing endogenous adenosine during ischemia may be cardioprotective, the objective of this study was to determine if adenosine deaminase inhibition with pentostatin could improve postischemic contractile dysfunction (stunning) in open-chest anesthetized dogs. All animals underwent 15 min of coronary occlusion followed by 3 h of reperfusion preceded by an intravenous bolus of either 0.2 mg/kg of pentostatin (n = 8) or saline (n = 7). Sonomicrometers were placed in the ischemic area and were used to measure systolic wall thickening before, during, and after occlusion of the left anterior descending artery. Myocardial blood flow was measured with tracer labeled microspheres at baseline, 10 min of occlusion and at 1 h of reperfusion. Both groups were equally dyskinetic during occlusion (-21 +/- 5% of baseline thickening in the controls and -28 +/- 8% in the pentostatin group). The pentostatin group, however, demonstrated better contractile function at all time points during reperfusion, which was significantly different from the control group at 3 h of reperfusion. The improvement in regional function in the pentostatin group was not due to significant disparities in hemodynamic variables, size of the region at risk, or in collateral blood flow. These results indicate that pentostatin can ameliorate the severity of myocardial stunning, an effect we propose is due to increasing endogenous levels of adenosine during the ischemic interval. Although significant improvement was detected with pentostatin, the improvement was modest compared to controls, suggesting that the utility of inhibiting adenosine deaminase to modify regional mechanical stunning is limited.

Effects of endothelin-receptor antagonism with PD156707 on myocardial stunning in swine.

Endothelin (ET) has been proposed to play a role in pathogenesis of myocardial ischemia/reperfusion injury. The potential role of ET in myocardial stunning has not been examined. Therefore we tested the hypothesis that selective blockade of ETA receptors with PD156707 {sodium 2-benzo[1,3]dioxol-5-yl-4-(4-methoxy-phenyl) -4-oxo-3-(3,4,5-trimethoxy-benzyl)-but-2-enoate} could improve postischemic contractile dysfunction in open-chest pigs. Myocardial stunning was achieved by a sequence of three 10-min left anterior descending (LAD) occlusions interspersed with 15 min of reperfusion. All pigs received either an intravenous saline vehicle (n =6) or PD156707 (n = 6) at a loading dose infusion of 10 mg/kg/h for 1 h before the first occlusion followed by a maintenance dose of 7 mg/kg/h for 4 h. Systolic wall thickening (percentage of baseline) was measured with sonomicrometers. There was no significant difference in systolic thickening between groups at baseline, at the end of the final stunning occlusion, or at any of the time points during reperfusion. PD156707 significantly reduced arterial blood pressure before myocardial ischemia and throughout reperfusion. There was no significant difference in size of the region at risk between groups. In conclusion, selective blockade of ETA receptors with PD156707 did not significantly alter postischemic contractile function in open-chest pigs. These results suggest that activation of ETA receptors by endogenous ET does not play a significant role in the pathogenesis of myocardial stunning.

CI-906 and CI-907: new orally active nonsulfhydryl angiotensin-converting enzyme inhibitors.

CI-906, [3S-[2[R*(R*)]], 3R*]-2-[2-[[1-(ethoxycarbonyl)-3-phenylpropyl]-amino]-1-oxopropyl] 1,2,3,4-tetrahydro-3-isoquinolinecarboxylic acid, monohydrochloride, and CI-907, [2S-[1[R*(R*)]], 2 alpha, 3a beta, 7a 7a beta]-1-[2-[[1-(ethoxycarbonyl)-3-phenylpropyl]amino] 1-oxopropyl]octahydro-1H-indole-2-carboxylic acid, monohydrochloride, are two new nonsulfhydryl-type angiotensin-converting enzyme (ACE) inhibitors. Monoester (prodrug) and diacid forms produced concentration-related ACE inhibition in guinea pig serum (IC50 for CI-906 = 8.3 X 10(-9) M, diacid = 2.8 X 10(-9) M; CI-907 = 1.0 X 10(-7) M, diacid = 2.6 X 10(-9) M). In isolated rabbit aortic rings and in in vivo rat and dog autonomic studies, both compounds were highly specific in suppressing the contractile or pressor responses to angiotensin I. In two-kidney, one-clip Goldblatt (renin-dependent) hypertensive rats there was a good correlation between the inhibition of vascular converting enzyme and blood pressure lowering and a poor correlation between blood pressure lowering and plasma and brain converting enzyme inhibition. Cardiovascular, pulmonary, and central nervous system performance evaluations showed no side effects or gross toxicity. The preclinical profile shows CI-906 and CI-907 to be specific, potent, orally active ACE inhibitors. They are expected to have therapeutic utility in hypertension and in any other condition where converting enzyme inhibition would be useful.

The antithrombotic effects of CI-1028, an orally bioavailable direct thrombin inhibitor, in a canine model of venous and arterial thrombosis.

Direct thrombin inhibitors represent a new class of drug that may offer a therapeutic alternative for the treatment and prevention of thrombembolic conditions, especially on the venous side of the systemic circulation. CI-1028 (PD 172524/LB30057) is a potent, highly selective inhibitor of thrombin that is orally bioavailable. The efficacy of this compound has been demonstrated in animal models in which intra-venous administration was used. The objective of this study was to evaluate the efficacy of CI-1028 after oral administration in a canine electrolytic injury model of venous and arterial thrombosis. CI-1028 was administered via oral gavage, and animals received either saline or 10, 15, 20, or 30 mg/kg of drug. Fifteen minutes later, the dogs were anesthetized and a femoral artery and vein were exposed and instrumented to induce electrolytic injury and thrombosis while continuously monitoring blood flow in the vessels. Maximum blood CI-1028 concentrations of 0.88+/-0.27, 1.8+/-0.3, 2.2+/-0.5, and 3.2+/-0.5 microg/mL were generally achieved 15 to 30 minutes after administering the compound in the 10-, 15-, 20-, and 30-mg/kg groups, respectively. Administration of CI-1028 increased the time to occlusion (TTO), the principal efficacy end point, in a dose-dependent manner in both arteries and veins. The TTO in the control group (n=8) averaged 66+/-11 minutes in the arteries and 69+/-6 minutes in the veins. In dogs treated with 10 mg/kg (n=8), the TTO was not significantly different from that of the control group. In the 15-mg/kg group (n=9) TTO averaged 140+/-27 minutes in the arteries (p=not significant) and 125+/-15 minutes (p<0.05) in the veins. In the 20-mg/kg group (n=8), TTO was significantly longer than controls in both types of vessels, averaging 168+/-30 minutes in the arteries (p=0.05) and 155+/-21 minutes (p<0.05) in the veins. Likewise, at 30 mg/kg (n=8) both the arterial (179+/-17 minutes) and venous (188+/-15 minutes) TTO was significantly prolonged compared with controls. Surgical blood loss and template bleeding times tended to increase in a dose-dependent manner but a statistically significant elevation was detected for template bleeding time only at the highest dose. Dramatic changes in thrombin time were detected, consistent with the CI-1028 mechanism of action. Virtually no changes were detected in prothrombin time. Maximum activated partial thromboplastin time (aPTT) and activated clotting time changes were detected approximately 30 minutes after dosing, and they were approximately twofold and fivefold baseline values, respectively, at the highest dose. In conclusion, these results demonstrate that CI-1028 provides dose-dependent antithrombotic efficacy after oral administration in a canine model of venous and arterial thrombosis.

Endothelin A receptor antagonism by PD 156707 does not reduce infarct size after coronary artery occlusion/reperfusion in pigs.

Episodes of myocardial ischemia are associated with increases in cardiac venous plasma endothelin (ET) concentrations, suggesting that ET may play a role in the development of myocardial infarction. The purpose of this study was to determine if selective blockade of ET(A) receptors by PD 156707 reduces infarct size caused by coronary artery occlusion and reperfusion in pentobarbital-anesthetized micropigs. A PD 156707 dose which selectively blocks the ET(A)-mediated vasopressor response, but not the ET(B)-mediated vasodepressor response to i.v. ET-1 challenges (0.3 nmol/kg), was established in dose ranging studies in anesthetized micropigs. In myocardial infarction studies, micropigs received either saline vehicle (n = 7) or PD 156707 (n = 8) at a loading dose of 10 mg/kg/1 hr, followed by a maintenance dose of 7 mg/kg/hr. Coinciding with the start of the maintenance dose, the left anterior descending coronary artery was occluded for 1 hr followed by 3 hr of reperfusion. PD 156707 caused a significant (29 mm Hg) decrease in arterial blood pressure before occlusion. PD 156707 had no effect on infarct size (61.1 +/- 5.6% of the region at risk in the PD 156707 treatment group vs. 70.1 +/- 3.9% in the control group). These results suggest that ET(A) receptor activation does not substantially contribute to coronary artery occlusion/reperfusion-induced myocardial infarction.

CI-926 (3-[4-[4-(3-methylphenyl)-1-piperazinyl]butyl]-2,4-imidazolinedione): antihypertensive profile and pharmacology.

CI-926 (10(-7)-10(-6) M) selectively antagonized the contraction of isolated rabbit aortae to phenylephrine and displaced the alpha-1 adrenoceptor ligand WB4101 (IC50: 82 nM) in rat brain. In the spontaneously hypertensive rat, single oral doses of either CI-926 (0.3-10 mg/kg) or prazosin (0.3-100 mg/kg) caused dose-related reductions in blood pressure; however, CI-926 was more efficacious. The maximal antihypertensive response to CI-926 was unchanged with three consecutive days of oral dosing in the spontaneously hypertensive rat, whereas a first dose effect was noted with prazosin. In two-kidney, one-clip, renal hypertensive rats, CI-926 and prazosin (1-10 mg/kg) lowered blood pressure; however, prazosin was more efficacious. In perinephritic hypertensive dogs, CI-926 (10 mg/kg) lowered blood pressure 20%. In anesthetized dogs, CI-926 in the presence of supermaximal blood pressure-lowering doses of prazosin caused an additional reduction in pressure. With equivalent alpha-1 blockade in anesthetized rats, CI-926 tended to have greater hypotensive activity than prazosin. These results demonstrate that CI-926 is a potent, orally active antihypertensive agent in renin-dependent and -independent hypertension. The profile of CI-926 suggests that it lowers blood pressure in part by interacting with peripheral alpha-1 adrenoceptors and in part via an additional mechanism(s). Although weak relative to its affinity for alpha-1 adrenoceptors, CI-926 was found in preliminary experiments to interact with alpha-2 adrenoceptors, serotonergic receptors and dopaminergic receptors. The importance of these interactions to the blood pressure response of CI-926 remains to be elucidated.

Cardiac hypertrophy in rats after intravenous administration of CI-959, a novel antiinflammatory compound: morphologic features and pharmacokinetic and pharmacodynamic mechanisms.

CI-959 is an antiallergic/antiinflammatory agent currently in development. In rats, daily bolus intravenous administration of CI-959 at doses > or = 10 mg/kg was associated with development of cardiac hypertrophy. There was no morphologic or biochemical evidence of myocyte injury, and cardiac hypertrophy rapidly reversed after treatment was discontinued. Cardiac hypertrophy was not evident when CI-959 was given orally or by continuous intravenous infusion with ALZA osmotic pumps. Maximum plasma drug concentrations (Cmax) were significantly higher when CI-959 was given by bolus intravenous injection, suggesting that cardiac effects were dependent on high Cmax concentrations. When neonatal rat cardiomyocytes were exposed to CI-959 in vitro, there was no evidence of myocyte enlargement or increased protein content. Cardiac hypertrophy was prevented by pretreatment with nonselective beta- and beta 1-selective adrenoceptor blockers as well as with central sympatholytics. beta 2- and alpha-adrenoceptor blockers were ineffective in preventing cardiac hypertrophy. Bolus intravenous CI-959 administration resulted in prolonged hypotension and associated increase in plasma catecholamine levels, with apparent inhibition of reflex tachycardia. We conclude that CI-959-associated cardiac hypertrophy in rats was not a direct drug effect but instead was probably mediated by endogenous catecholaminergic stimulation of cardiac beta 1-adrenoceptors.