Direct thrombin inhibitors, but not the direct factor Xa inhibitor rivaroxaban, increase tissue factor-induced hypercoagulability in vitro and in vivo.

BACKGROUND: Increased hypercoagulability has been reported with low doses of direct thrombin inhibitors but not with direct factor Xa inhibitors. OBJECTIVES: To compare the effects of rivaroxaban with those of melagatran and dabigatran on thrombin generation (TG) and tissue factor-induced hypercoagulability and to explore the possible involvement of the thrombin-thrombomodulin/activated protein C system. METHODS: In normal human plasma and in protein C-deficient plasma, TG was investigated in vitro in the presence and absence of recombinant human soluble thrombomodulin (rhs-TM). TG was determined by calibrated automated thrombography and an ELISA for prothrombin fragments 1+2 (F1+2 ). In an in vivo rat model, hypercoagulability was induced by tissue factor; levels of thrombin-antithrombin (TAT) and fibrinogen and the platelet count were determined. RESULTS: Rivaroxaban inhibited TG in a concentration-dependent manner. In the absence of rhs-TM, melagatran and dabigatran also inhibited TG concentration dependently. However, in the presence of rhs-TM, lower concentrations of melagatran (119-474 nmol L(-1) ) and dabigatran (68-545 nmol L(-1) ) enhanced endogenous thrombin potential, peak TG, and F1+2 formation in normal plasma but not in protein C-deficient plasma. In vivo, rivaroxaban dose-dependently inhibited TAT generation, whereas melagatran showed a paradoxical effect, with an increase in TAT and a small decrease in fibrinogen and platelet count at lower doses. CONCLUSION: Low concentrations of the direct thrombin inhibitors melagatran and dabigatran enhanced TG and hypercoagulability, possibly via inhibition of the protein C system. In contrast, rivaroxaban reduced TG and hypercoagulability under all conditions studied, suggesting that it does not suppress this negative-feedback system.

Effects of rivaroxaban, acetylsalicylic acid and clopidogrel as monotherapy and in combination in a porcine model of stent thrombosis.

BACKGROUND: Despite standard dual antiplatelet therapy (DAT) (acetylsalicylic acid [ASA] and clopidogrel), there is a ≥ 1.4% incidence of in-stent thrombosis in patients with acute coronary syndrome. Factor Xa inhibitors are being investigated for secondary prevention after acute coronary syndrome. OBJECTIVE: To study the antithrombotic effects of the FXa inhibitor rivaroxaban alone or in combination with DAT. METHODS: Bare metal stents (12 per animal, three per intervention period) were deployed in a porcine ex vivo arteriovenous shunt and exposed to flowing arterial blood (shear rate: 1500 s(-1)). In-stent thrombus formation was analyzed under different treatments: vehicle (n = 7 animals); intravenous (i.v.) rivaroxaban (0.11, 0.33, and 1.0 µg kg(-1) min(-1)) (n = 8); rivaroxaban + ASA (1.0 mg kg(-1) i.v.) (n = 6); rivaroxaban + ASA (1.0 mg kg(-1) i.v.) + clopidogrel (0.5 mg kg(-1) i.v.) (n = 7); and ASA (1.0 mg kg(-1) i.v.) + clopidogrel (0.5 mg kg(-1) i.v.) (n = 6). RESULTS: Rivaroxaban dose-dependently reduced stent thrombus weight by ≤ 66% vs. vehicle (P < 0.05, all doses). Rivaroxaban + ASA further reduced thrombus weight vs. vehicle (86% at the highest rivaroxaban dose; P < 0.001). DAT reduced thrombus weight by ≤ 79%. However, rivaroxaban + ASA + clopidogrel almost completely abolished in-stent thrombus formation (98% reduction vs. vehicle at the highest rivaroxaban dose; P < 0.001). CONCLUSIONS: Our data on the inhibitory effect of rivaroxaban alone or with DAT are consistent with the ATLAS 2 trial findings, and support its potential use for preventing stent thrombosis after stent deployment.

Factor Xa inhibitors--new anticoagulants for secondary haemostasis.

Oral factor Xa (FXa) inhibitors are a promising alternative to current anticoagulants. This paper reviews the latest developments of oral direct FXa inhibitors and focuses on those which have been approved for the prevention of venous thromboembolism (VTE) after total hip or knee replacement or are in advanced development and have passed phase II (proof of principle) testing. The most advanced drugs are apixaban, betrixaban, edoxaban, eribaxaban, rivaroxaban, LY517717, TAK-442, and YM150. Rivaroxaban (Xareltoâ) is the first direct FXa inhibitor which has recently been approved for the prevention of VTE in adult patients after elective hip or knee replacement in several countries, including the European Union and Canada. Rivaroxaban has a flat dose-dependent anticoagulant response with a wide therapeutic window and low potential for drug-drug and drug-food interactions. Rivaroxaban can be given in fixed doses without coagulation monitoring. This review describes the pharmacodynamic and pharmacokinetic profiles and the results of clinical trials with FXa inhibitors in the prevention and treatment of thromboembolic disorders.

Rivaroxaban. A novel, oral, direct factor Xa inhibitor in clinical development for the prevention and treatment of thromboembolic disorders.

Rivaroxaban (Xarelto) is a novel, oral, direct Factor Xa (FXa) inhibitor in late-stage development for the prevention and treatment of thromboembolic disorders. Rivaroxaban inhibits clot-associated and free FXa activity, and prothrombinase activity, and reduces thrombin generation. In animal models, rivaroxaban prevented venous and arterial thrombosis, and was effective at treating venous thrombosis. Rivaroxaban has high oral bioavailability, a rapid onset of action and predictable pharmacokinetics. In phase II studies, rivaroxaban was effective and well tolerated for the prevention of venous thromboembolism (VTE) after major orthopaedic surgery, and for the treatment of deep vein thrombosis. In a phase III study, rivaroxaban demonstrated significantly superior efficacy to enoxaparin for thromboprophylaxis after total knee arthroplasty, with similar low bleeding. Rivaroxaban is also being assessed for the treatment and secondary prevention of VTE, prevention of stroke in patients with atrial fibrillation and secondary prevention in patients with acute coronary syndrome. Rivaroxaban is a promising alternative to current pharmacological agents for thromboembolic disorders.

In vitro and in vivo studies of the novel antithrombotic agent BAY 59-7939--an oral, direct Factor Xa inhibitor.

BAY 59-7939 is an oral, direct Factor Xa (FXa) inhibitor in development for the prevention and treatment of arterial and venous thrombosis. BAY 59-7939 competitively inhibits human FXa (K(i) 0.4 nm) with > 10 000-fold greater selectivity than for other serine proteases; it also inhibited prothrombinase activity (IC(50) 2.1 nm). BAY 59-7939 inhibited endogenous FXa more potently in human and rabbit plasma (IC(50) 21 nm) than rat plasma (IC(50) 290 nm). It demonstrated anticoagulant effects in human plasma, doubling prothrombin time (PT) and activated partial thromboplastin time at 0.23 and 0.69 microm, respectively. In vivo, BAY 59-7939 reduced venous thrombosis (fibrin-rich, platelet-poor thrombi) dose dependently (ED(50) 0.1 mg kg(-1) i.v.) in a rat venous stasis model. BAY 59-7939 reduced arterial (fibrin- and platelet-rich) thrombus formation in an arteriovenous (AV) shunt in rats (ED(50) 5.0 mg kg(-1) p.o.) and rabbits (ED(50) 0.6 mg kg(-1) p.o.). Slight inhibition of FXa (32% at ED(50)) reduced thrombus formation in the venous model; to affect arterial thrombosis in the rat and rabbit, stronger inhibition of FXa (74%, 92% at ED(50)) was required. Calculated plasma levels in rabbits at the ED(50) were 14-fold lower than in the rat AV shunt model, correlating with the 14-fold lower IC(50) of FXa inhibition in rabbit compared with rat plasma; this may suggest a correlation between FXa inhibition and antithrombotic activity. Bleeding times in rats and rabbits were not significantly affected at antithrombotic doses (3 mg kg(-1) p.o., AV shunt). Based on these results, BAY 59-7939 was selected for clinical development.

NO-independent regulatory site on soluble guanylate cyclase.

Nitric oxide (NO) is a widespread, potent, biological mediator that has many physiological and pathophysiological roles. Research in the field of NO appears to have followed a straightforward path, and the findings have been progressive: NO and cyclic GMP are involved in vasodilatation; glycerol trinitrate relaxes vascular smooth muscles by bioconversion to NO; mammalian cells synthesize NO; and last, NO mediates vasodilatation by stimulating the soluble guanylate cyclase (sGC), a heterodimeric (alpha/beta) haem protein that converts GTP to cGMP2-4. Here we report the discovery of a regulatory site on sGC. Using photoaffinity labelling, we have identified the cysteine 238 and cysteine 243 region in the alpha1-subunit of sGC as the target for a new type of sGC stimulator. Moreover, we present a pyrazolopyridine, BAY 41-2272, that potently stimulates sGC through this site by a mechanism that is independent of NO. This results in antiplatelet activity, a strong decrease in blood pressure and an increase in survival in a low-NO rat model of hypertension, and as such may offer an approach for treating cardiovascular diseases.

BAY X1005, a new inhibitor of leukotriene synthesis: in vivo inflammation pharmacology and pharmacokinetics.

(R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) (BAY X1005) is an orally active inhibitor of the synthesis of the leukotrienes B4 and C4 in selected animal models that effectively reduces the vascular phenomena of inflammation, i.e., edema formation and leukocyte immigration. The arachidonic acid-induced mouse ear inflammation test allowed the evaluation of the antiedematous effects of BAY X1005 after topical (ED50, 18 micrograms/ear) and oral (ED50, 48.7 mg/kg) administration. Profound inhibition of myeloperoxidase activity as a marker for phagocyte infiltration was seen (ED50, 3 micrograms/ear topically and 7.9 mg/kg p.o.) even 5 hr after application. The platelet-activating factor-induced death of mice was statistical significantly and dose-dependently reduced (100 mg/kg p.o.; mean, 51%). BAY X1005 had no analgesic properties in the phenyl-benzoquinone writhing test in mice and only limited efficacy in the baker's yeast-induced hyperalgesia test in the rat (ED50, 90 mg/kg p.o.), although cyclooxygenase inhibitors (indomethacin ED50, 1.7 mg/kg p.o.) are very potent. In another cyclooxygenase-sensitive test, the carrageenan-induced edema and the baker's yeast-induced fever in the rat, BAY X1005 was virtually devoid of any activity. The rat whole blood ex vivo leukotriene B4 inhibition assay demonstrated that BAY X1005 was potent (ED50, 11.8 and 6.7 mg/kg p.o. at 1 and 5 hr, respectively) and had a long duration of action (16-hr ED40, 70 mg/kg p.o.). Similarly, inhibition of the zymosan-induced exudate leukotrienes B4 and C4 inhibition confirmed these data (ED50, 8.3 and 10.5 mg/kg p.o., respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Binding characteristics of the new thromboxane A2/prostaglandin H2 receptor antagonist [3H]BAY U 3405 to washed human platelets and platelet membranes.

The new thromboxane A2 antagonist [3H]BAY U 3405 was characterized for its binding to washed human platelets and platelet membranes. In washed platelets the specific binding was reversible, selective and stereospecific, but not saturable. The dissociation constant (Kd) was 6 +/- 2.5 nM, the number of specific binding sites 1177 +/- 306 per platelet. Three structurally different thromboxane A2 (TXA2)/prostaglandin H2 (prostaglandin endoperoxide) (PGH2) receptor ligands completely inhibited the specific binding of [3H]BAY U 3405 in a concentration-dependent manner, indicating that the observed high affinity binding site is the TXA2/PGH2 receptor. In platelet membranes, however, specific [3H]BAY U 3405 binding showed saturability in addition to reversibility, selectivity, and stereospecifity. The Kd of the binding was 9.6 +/- 2.3 nM in kinetic studies and 8.7 +/- 3.7 nM in saturation studies, the inhibition constant (Ki) was 10 +/- 1.1 nM in displacement studies. The TXA2/PGH2 receptor agonists U 46619 and CTA2, and the antagonists Daltroban (BM 13505), I-PTA-OH and SQ 29548 all completely inhibited the specific binding of [3H]BAY U 3405 thus defining the observed binding site as the TXA2/PGH2 receptor. In conclusion, the data suggest that the previously reported TXA2 antagonism of BAY U 3405 is mediated by binding to a specific high affinity binding site of human platelets and platelet membranes that represents the TXA2/PGH2 receptor.

pH dependency of the binding of [3H]BAY U 3405 and various non-labelled ligands to the thromboxane A2/prostaglandin H2 receptor of human platelet membranes.

[3H]BAY U 3405 was used to characterize the effect of acidic and alkaline pH values on the binding of the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor of human platelet membranes. The specific binding of [3H]BAY U 3405 largely increased upon acidification up to pH 5.8. Saturation binding studies revealed an increase in binding affinity without change in the number of binding sites. At pH 7.4 the Kd was 8.7 +/- 3.7 nM (Bmax = 6.6 +/- 0.6 pmol/mg protein) compared to 1.2 +/- 0.2 nM (Bmax = 6.1 +/- 0.6 pmol/mg protein) at pH 5.8. A more than 10-fold higher rate of association was observed at pH 5.8 compared to pH 7.4, while the rate of dissociation showed only minor changes. The kinetically derived dissociation constant was 1 nM (pH 5.8) and 9.6 nM (pH 7.4). The pH dependency of the binding of structurally different non-labelled ligands to the TXA2/PGH2 receptor was evaluated by inhibition studies at pH 5.8 and pH 7.4. BAY U 3405, daltroban, CTA2, and U 46619 showed significantly higher affinities at pH 5.8. In contrast, I-PTA-OH and GR 32191 had a higher affinity at pH 7.4. No significant difference was seen with SQ 29548 at the observed pH values. A second protonable group within the molecules I-PTA-OH, GR 32191, and SQ 29548 might be responsible for the observed differences.

pH-dependent binding of the TXA2/PGH2-receptor of human platelet membranes to various ligands.

[3H]-BAY U 3405 was used to characterize the pH-dependency of the binding of various ligands to the TXA2/PGH2-receptor of human platelet membranes. Maximum binding of [3H]-BAY U 3405 is achieved at pH 5.8. In inhibition studies the ligands Daltroban, CTA2, and U 46619 also show a higher affinity at pH 5.8 compared to pH 7.4. In contrast, the ligands I-PTA-OH and GR 32191 have a higher affinity at pH 7.4. No difference is seen with SQ 29548. The ligands I-PTA-OH, GR 32191, and SQ 29548 have a second protonable group in common, which is thought to be the reason for the different pH-dependent binding.

Effect of BAY U 3405, a new thromboxane antagonist, on sudden death in rabbits.

We studied the effects of BAY U 3405 in experimental models of arachidonic acid- and collagen-induced sudden death. BAY U 3405 was effective in dose-dependently inhibiting death from both arachidonic acid and collagen at doses of 1, 3 and 10 mg/kg orally. The survival rate, usually amounting to less than 10% in vehicle-treated animals, was dramatically increased to 100% at the highest dose. The data obtained emphasize the role of thromboxane A2 as a mediator in this model, and the potential usefulness of BAY U 3405 for thromboembolic disorders.

Protective effect of a novel thromboxane antagonist, BAY-U3405, on canine myocardial damage after coronary artery occlusion and reperfusion.

The effects of a novel thromboxane antagonist, (3R)-3-(4-fluorophenylsulfonmido)-1,2,3,4-tetrahydro-9-carbazol epropanoic acid (BAY-U3405), on myocardial damage due to ischemia and reperfusion (added to accelerate the initiated injury) were studied in anesthetized dogs. The left anterior descending (LAD) coronary artery was occluded for 6 hours and reperfused for 30 minutes. BAY-U3405, 1 mg/kg, was injected intravenously 15 minutes after LAD occlusion, followed by continuous infusion of 10 mg/kg/hour starting at 30 minutes after occlusion. The drug had no hemodynamic effects. During the experiments 6 of 14 animals died of ventricular fibrillation (VF) in the placebo-vehicle controls (3 during occlusion and 3 during reperfusion); in the drug-treated group 5 of 13 dogs died of VF (all during occlusion none during reperfusion). This difference in total mortality and cause was not statistically significant. Reperfusion arrhythmias were largely suppressed by BAY-U3405: 201 +/- 43 versus 689 +/- 98 irregular beats during 30 minutes (p less than 0.001) in the experimental and control groups, respectively. Coronary collateral flow, obtained from a load-line analysis by measurement of retrograde coronary flow, and collateral index were similar in both groups. Therefore, BAY-U3405 did not alter collateral blood supply to the ischemic myocardium. Infarct size, determined with tetrazolium staining, was reduced by 65% (p less than 0.01) after its administration. These results suggest that thromboxane antagonism by BAY-U3405 may delay infarct expansion and reduce the frequency of ventricular arrhythmias during reperfusion of previously ischemic myocardium.

Effect of BAY U 3405, a new thromboxane antagonist, on arachidonic acid induced thromboembolism.

The model of AA-induced sudden death employed in these investigations seems to be appropriate for studying the efficacy of TXA2-antagonists. The actions of TXA2 on platelets, respiratory and vascular tissue are considered as key events resulting in the death of the animals. The results obtained in this study, using BAY U 3405 as a selective TXA2 receptor antagonist, clearly show that TXA2 mediated processes are effectively abolished by this type of drug. Since TXA2 is implicated in the pathophysiology of many diseases, potent TXA2 antagonists appear to be useful for treatment of these disorders. BAY U 3405 seems to fulfil these requirements. The threshold dose is 1 to 3 mg/kg p.o. In addition, there is a rapid onset and long duration of action at 10 mg/kg p.o. under the experimental conditions used.

Effect of Bay U 3405, a new thromboxane antagonist, on collagen-induced thromboembolism in rabbits.

Bay U 3405 [(3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9- carbazolepropanoic acid] potently inhibits platelet aggregation, thromboxane A2-induced contraction of smooth muscles, and coronary artery thrombosis. We have previously demonstrated inhibition of arachidonic acid-induced sudden death by Bay U 3405. The purpose of this study was to investigate the effects of Bay U 3405 on thromboembolism provoked by collagen. Collagen fibrils dissolved in an isotonic glucose solution were injected into a marginal ear vein of anesthetized rabbits. Sudden death occurred within a few minutes due to elevated thromboxane A2 levels causing intravascular platelet aggregation and myocardial ischemia. In the vehicle-treated group, 100% of the animals died. One of the most prominent parameters was the massive fall in blood pressure. All animals pretreated with 10 mg/kg orally Bay U 3405 survived, showing only a transient hypotensive effect. Tracings of the electrocardiogram and heart rate were unchanged. Bay U 3405 will therefore be useful to elucidate the role of thromboxane A2 in various cardiovascular and respiratory diseases.

Effects of the novel thromboxane antagonist Bay U 3405 on experimental coronary artery disease.

Bay U 3405 is a novel thromboxane receptor blocker. The present investigations describe its effects on experimental canine and porcine cardiac damage. In anesthetized dogs, a coronary artery was occluded for 6 hours and reperfused for 30 minutes. Bay U 3405 was administered intravenously 15 minutes after occlusion (1 mg/kg) followed by infusion of 10 mg/kg/hr from 30 minutes after ligature. In a second study, the effects of Bay U 3405 on endoperoxide analogue U-46619-induced coronary constriction were studied in anesthetized, open-chest pigs. Bay U 3405 reduced myocardial infarct expansion by 65% (p less than 0.01) assessed with biochemical staining. Hemodynamics and collateral blood flow were unaffected. However, reperfusion arrhythmias were suppressed. In porcine experiments, 1 mg/kg Bay U 3405, given intravenously or intraduodenally, antagonized U-46619-induced coronary vasoconstriction over 5 hours. The studies demonstrate anti-ischemic and antivasoconstrictor properties of Bay U 3405 probably due to binding to platelet and smooth muscle thromboxane receptors. This may have clinical relevance in angina pectoris and myocardial infarction.

Characterization of Bay U 3405, a novel thromboxane A2/endoperoxide receptor antagonist.

The thromboxane A2-receptor antagonistic properties of Bay U 3405 [(3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz o-lepropanoic acid] have been evaluated in various pharmacologic models. Bay U 3405 specifically inhibits platelet aggregation induced by U 46619, collagen, platelet-activating factor, and the second wave of ADP (IC50 0.5, 0.07, 0.3, 0.19 microM) in human plasma. The plasma phase of ADP-induced aggregation is not affected. U 46619-induced platelet aggregation is competitively antagonized (pA2 = 6.3). In humans, ex vivo platelet aggregation is inhibited after oral application of 2 or 50 mg Bay U 3405. Bay U 3405 also specifically and competitively antagonizes U 46619-induced contractions of rabbit aortic rings (pA2 = 7.4). In vivo, Bay U 3405 protects rabbits dose dependently from arachidonic acid or collagen-induced thromboembolism (ED50 1-3 mg/kg p.o). Chronic administration of Bay U 3405 to stroke-prone spontaneously hypertensive rats reduces stroke-related mortality and diminishes the occurrence of cerebral hemorrhages. From these results, we conclude that Bay U 3405 is an orally active, selective, and competitive thromboxane A2-receptor antagonist that may be beneficial in the treatment of cardiovascular or cerebrovascular diseases.

Synthesis and absolute configuration of the new thromboxane antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazolepropan oic acid and comparison with its enantiomer.

The synthesis of (3R)-3-(4-Fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9- carbazolepropanoic acid (Bay u 3405), a new, enantiomerically pure antagonist of thromboxane A2, is described. The determination of the absolute configuration of Bay u 3405 was performed by an X-ray analysis of compound 7 ([3((2S)-acetylamido)-3-phenylpropionamido]-1,2,3,4- tetrahydro-carbazol). Bay u 3405 is in vitro 1 to 2 orders of magnitude more active than its (-)-enantiomer Bay u 3406.

Action of the novel selective thromboxane antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazolepropan oic acid on vascular smooth muscle preparations.

The action of the thromboxane A2-receptor-antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazo lepropanoic acid (Bay u 3405) on vascular smooth muscle preparations was investigated in vitro. In rabbit aortic rings Bay u 3405 is a potent inhibitor of vasoconstriction produced by thromboxane A2 (TXA2)/PG endoperoxides generated by stimulated human platelets (EC50 1.3 x 10(-6) mol/l), (+/-)-cTA2 (Carbocyclic thromboxane A2 [2 beta(Z),3 alpha-(1E,3R*)-3- (3-hydroxy(1-octenyl)-bicyclo[3.1.1]hept-2-yl-5-heptenoic acid]) (EC50 3.3 x 10(-7) mol/l) and U 46619 (EC50 3.8 x 10(-7) mol/l). In pig circumflex coronary arteries Bay u 3405 was 150 times more potent (EC50 2.6 x 10(-9) mol/l) than in rabbit aorta. In rabbit and rat aorta the concentration-response curves for U 46619 were shifted to the right in a parallel manner and the maximum responses were not suppressed. The Schild-plot yielded a straight line with a slope of 1.14 (rabbit) or 1.29 (rat) and pA2 values of 7.43 and 8.59, respectively. The vasoconstrictive action of other agonists such as KCl, serotonin, histamine, epinephrine, norepinephrine, acetylcholine and angiotensin were not affected. In human platelets inhibition of the TXA2-synthase was seen only at concentrations of Bay u 3405 of 2.4 x 10(-5) mol/l and above. From these findings it is concluded that Bay u 3405 is a potent, competitive TXA2/endoperoxide receptor antagonist in vascular smooth muscle.

Inhibition of platelet aggregation in vitro and ex vivo by the new thromboxane antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9- carbazolepropanoic acid.

(3R)-3-(4-Fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazo lepropanoic acid (Bay u 3405) was tested for inhibition of platelet aggregation in vitro (human platelet rich plasma) and ex vivo (rat). Aggregation induced by collagen, arachidonic acid, thrombin, adenosine diphosphate (ADP, biphasic response), epinephrine and U 46619 was inhibited at minimum effective concentrations of 0.01 to 0.1 micrograms/ml in vitro. Following oral administration to rats the ED50 for the dose-dependent inhibition was 36 micrograms/kg. At a dose of 100 micrograms/kg p.o. significant inhibition was obtained up to 16 h. Bay u 3405 is considered a potential drug for treatment of some cardiovascular disorders.