[Show abstract][Hide abstract] ABSTRACT: We attempted to clarify the usefulness of transesophageal echocardiography performed using a standardized Valsalva maneuver to detect the presence of a patent foramen ovale in Japanese patients with ischemic stroke. Four hundred ninety six patients with ischemic stroke who were admitted to the Yokohama City Brain and Stroke Center between September 1999 and February 2002 were enrolled for the study. All the enrolled patients underwent transesophageal echocardiography with contrast injection and color Doppler imaging. During the procedure, a standardized Valsalva maneuver was performed to induce right to left shunting through a patent foramen ovale. Other related structural abnormalities, such as atrial septal aneurysm and the Chiari network anomaly, were also detected by the test. Transesophageal echocardiography without the Valsalva maneuver revealed a functional right to left communication in only 8.2% of the ischemic stroke patients, whereas the procedure conducted using a standardized Valsalva maneuver to provoke shunting revealed a patent foramen ovale in 15.3% of the patients. The presence of an atrial septal aneurysm or the Chiari network anomaly was not sensitive or specific enough to predict the presence of a patent foramen ovale as diagnosed by transesophageal echocardiography using the standardized Valsalva maneuver. Our results suggest that the standardized Valsalva maneuver is a safe and useful technique to detect the presence of a patent foramen ovale, which is potentially known to be associated with paradoxical embolism.
Preview · Article · Jan 2006 · The Tokai journal of experimental and clinical medicine
[Show abstract][Hide abstract] ABSTRACT: Since the clinical profile and prognosis of heart failure depending on time of the study performed, regional characteristics of background population and different race, we attempted to evaluate the prognosis of symptoms and life expectancy of Japanese patients with heart failure. We evaluated the clinical profiles and prognoses of 1,015 consecutive patients with congestive heart failure (CHF) for whom hospitalization was required. A total of 1,015 consecutive CHF patients (584 males and 431 females) were enrolled in this study, however the total number of events investigated was 1,409. Of these patients, survival was confirmed in 413 patients, death was confirmed in 299 patients, and the prognoses of 303 patients remained unknown due to transfer to other hospitals or for some other reasons. The mean age on admission was 68.4 +/- 14.9 years. In both males and females, the peak age at the onset of CHF was in the seventies, and for patients in their eighties, the number of female patients with CHF was larger than that of male patients. Major underlying heart diseases consisted of ischemic heart disease (34%), valvular heart disease (22%), dilated cardiomyopathy (11%), and hypertension (10%). Most CHF patients who had dilated cardiomyopathy as an underlying disease were hospitalized several times, and 45% of them were hospitalized 3 times or more. The life expectancy of patients with CHF caused by ischemic heart disease was the poorest, and their 5-year and 10-year survival rates were 55% and 38%, respectively. Similarly, 5-year and 10-year survival rates of patients with CHF caused by valvular heart disease, hypertension, and dilated cardiomyopathy were 62% and 44%, 58% and 53%, and 70% and 65%, respectively. In 299 deceased patients, the mean age at death was 72.2 +/- 13.9 years. In all these deceased patients, direct causes of death were sudden death (16.1%), CHF (42.2%), others (31.4%), and unknown (10.4%). The frequency of sudden death was highest (25%) in patients with CHF caused by dilated cardiomyopathy, followed by those with CHF caused by valvular heart disease (18%) and those with CHF caused by ischemic heart disease (17.5%). In addition, the frequency of death from CHF was highest (60%) in those with CHF caused by dilated cardiomyopathy, followed by those with CHF caused by ischemic heart disease (49.2%).
Preview · Article · Oct 2005 · The Tokai journal of experimental and clinical medicine
[Show abstract][Hide abstract] ABSTRACT: Low density lipoprotein (LDL)-apheresis is a useful tool for the treatment of familial hypercholesterolemia (FH) with coronary artery disease (CAD). However, it gives economic, physical and mental burdens for the patients. We reports a case of FH in whom LDL-apheresis treatment was seceded with drug treatment with a potent statin and bile acid-sequestering resin. A 54-year-old woman was admitted for evaluation of atherosclerotic lesion after 4 years of LDL-apheresis and 1 year of drug medication with a potent statin, atorvastatin and resin, cholestimide with coronary angiography. She had been diagnosed as heterozygous FH when she was 46 years old. Oral medication was initiated at the outpatient clinic. LDL-cholesterol (C) level was not successfully controlled despite the administration of a statin, pravastatin, a fibrate, clinofibrate and probucol at maximum doses Concomitantly. Therefore, as combination therapy, LDL-apheresis was introduced in May 1997. However, the patient strongly complained of the economic, physical, and mental burdens of LDL-apheresis and requested discontinuation of apheresis. Therefore, LDL-apheresis was discontinued in July 2000, and oral medication was subsequently changed to a combination of atorvastatin and cholestimide, resulting in successful control of serum LDL-C level by oral medication alone. We compared coronary arteriographic findings between 1997 and 2001. No advancement of lesions was observed. We think that strong drug treatment can secede from the LDL-apheresis for treatment of patients with FH.
Preview · Article · Oct 2005 · The Tokai journal of experimental and clinical medicine
[Show abstract][Hide abstract] ABSTRACT: There is evidence for immune system involvement in atherogenesis. In the present study the effect of platelets on dendritic cells (DC), an important immunologic regulator, was examined in vitro. Platelet-rich plasma, after exposure to shear stress, was added to human monocyte-derived immature DC, which were then examined for surface Ag expression, allogeneic T lymphocyte stimulatory activity, and cytokine production. After exposure, the number of anti-CD40 ligand (anti-CD40L) and anti-P-selectin IgG molecules bound per platelet was increased. These activated platelets induced DC maturation, as revealed by significant up-regulation of CD83, CD80, and CD86 Ags. The addition of platelets in the presence of IFN-gamma plus LPS significantly enhanced IL-10 production from immature DC. After platelet addition, mature DC provoked a significant proliferation of allogeneic naive T lymphocytes. These activated T cells showed lower IFN-gamma production than those stimulated by LPS- and IFN-gamma-treated DC. CD40L on the platelet surface was not involved in maturation of DC, as mAb to CD40L failed to block maturation. The effect of platelets was observed even if platelets and DC were separated using large pore-sized membranes or when platelets were depleted from plasma by centrifugation. Furthermore, it was abrogated after the depletion of protein fraction. Thus, soluble protein factors excreted from activated platelets contribute to IL-10-producing DC maturation.
Preview · Article · Jun 2004 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Ilexonin A (IA), purified from the Chinese herbal medicine Maodongqing (Ilex pubescens Hook, et Arn) has been commonly used in south China to treat thrombotic disorders. In this study, we aimed to study the inhibiting effects and mechanism of IA on von Willebrand factor (vWF)-dependent high shear-induced platelet aggregation.
vWF-dependent high shear (10,800 s(-1)) induced aggregation of platelets obtained from normal donors in the presence or absence of IA was measured by a modified cone-plate viscometer and shear-induced vWF binding was measured by quantitative flow cytometry with monoclonal antibody known to bind exclusively to the C-terminal domain of vWF (LJ-C3) directly labeled with fluorescein isothiocyanate (FITC). P-selectin surface expression was also measured by a similar method with FITC conjugated anti-P-selectin monoclonal antibody (WGA1).
Shear-induced platelet aggregation was inhibited by IA in a dose-dependent manner. The extent of aggregation decreased from (78.6 +/- 4.6)% in the absence of IA to (36.5 +/- 2.1)% in the presence of IA (3.3 mmol/L) (P < 0.0001, n = 9) with a high shear rate of 10800 s(-1). vWF binding and P-selectin expression were also inhibited by IA in a dose dependent manner. The number of binding FITC-LJ-C3 molecules increased after exposure of platelet-rich plasma to a high shear rate of 10800 s(-1) for 6 minutes, but this shear-induced increased binding platelet surface vWF molecules and P-selectin expression can be decreased in the presence of IA.
vWF binding and vWF mediated platelet activation, aggregation occurring under high shear rate were inhibited by IA. IA may be a unique antithrombotic drug inhibiting the vWF-GP Ibalpha interaction, and may thus facilitate drug design targeting arterial thrombosis.
Preview · Article · Feb 2004 · Chinese medical journal
[Show abstract][Hide abstract] ABSTRACT: Inhibitors of the platelet glycoprotein (GP)IIb-IIIa receptor (integrin alphaIIbbeta3) reduce acute thrombotic events in patients with coronary artery disease. To characterize the mechanism of action of these drugs, we evaluated the effects of different GPIIb-IIIa antagonists on shear-induced platelet aggregation, activation, and the expression of procoagulant activity. Samples of platelet-rich plasma from 16 volunteers were exposed to the shear rate of 10 800 s-1 for 6 min in an optically modified cone-plate viscometer. Abciximab, tirofiban and eptifibatide inhibited aggregation to a similar extent (mean +/- SD: 74.1 +/- 8.5%, 69.5 +/- 13.6%, 65.6 +/- 17.0%, respectively), but only abciximab inhibited significantly microparticle release associated with shear-induced platelet activation (64.4 +/- 13.6%, P = 2.2 x 10-7; tirofiban = 20.0 +/- 23.4%; eptifibatide = 23.9 +/- 17.4%). P-selectin platelet surface translocation was also strongly inhibited by abciximab, weakly by eptifibatide, but not by tirofiban. The addition of anti-alphavbeta3 to tirofiban enhanced the inhibiting effects on shear-induced P-selectin translocation and microparticle release. Shearing of platelet-rich plasma shortened the re-calcification clotting time after addition of kaolin from 106.9 +/- 14.3 to 94.2 +/- 10.7 s (mean +/- SD; P = 0.0013). This effect, which is mediated by the appearance of procoagulant phospholipids on the surface of sheared platelets and microparticles, was prevented by abciximab and by the combination of tirofiban and anti-alphavbeta3, but not by tirofiban alone or eptifibatide. The ability to inhibit shear-induced platelet activation, as evidenced by microparticle release and P-selectin surface translocation as well as the expression of procoagulant activity, differentiates the effects of anti-GPIIb-IIIa agents, which may explain the distinct antithrombotic efficacy of the agents.
Full-text · Article · Oct 2003 · Journal of Thrombosis and Haemostasis
[Show abstract][Hide abstract] ABSTRACT: Class I antiarrhythmic agents are not always effective in the treatment of life-threatening ventricular tachycardia/ventricular fibrillation (VT/VF) especially in patients with cardiopulmonary arrest. Nifekalant hydrochloride(NIF) is a novel class III antiarrhythmic agent for malignant VT/VF. This study prospectively evaluated NIF efficacy for life-threatening VT/VF observed after cardiopulmonary arrest.
Thirty-two of 145 patients who were transferred to the emergency room in Tokai University Hospital showed VT/VF after resuscitation from cardiopulmonary arrest from June 2000 to March 2001. These 32 patients were treated with 12 mg (mean) epinephrine and 1.0-2.0 mg/kg lidocaine following direct current application(200 to 360J), and then classified into two groups. Eleven patients received intravenous 0.15 to 0.3 mg/kg NIF followed by intravenous infusion of 0.3 to 0.4 mg/kg/hr NIF(NIF group). The other 21 patients received 1.0 to 2.0 mg/kg of lidocaine(non-NIF group).
Sinus rhythm was restored in the nine patients(82%) in the NIF group but only four patients (19%) in the non-NIF group. QTc was not prolonged(0.45 +/- 0.04 sec, n = 9) and no torsades de pointes was observed in the NIF group. Two patients survived but the remaining nine patients died in the NIF group. Five patients died of cardiac standstill following sinus bradycardia and repeated sinus arrest within 2 to 27 hr after admission, two patients died of sudden cardiac arrest from sinus rhythm, and two patients died of persistent VT/VF. In contrast, all 21 patients in the non-NIF group died. Seventeen patients died of persistent VT/VF before hospitalization, one patient died of recurrent VT/VF, and three patients died of cardiac standstill following sinus bradycardia.
NIF effectively suppresses VT/VF which is refractory to direct current shock in patients with cardiopulmonary arrest. However, NIF may rather worsen electrophysiological function in the sinus node after administration of high doses of epinephrine, and may induce sinus bradycardia and/or sinus arrest. Careful observation, such as monitoring of electrocardiography and blood pressure and temporary cardiac pacemaker use, is needed to prevent death in patients surviving after cardiopulmonary arrest if NIF is administered following high dose epinephrine infusion.
No preview · Article · Apr 2003 · Journal of Cardiology
[Show abstract][Hide abstract] ABSTRACT: Thrombocytopenia is recognized as one of the most common complications when the patients with severe heart failure are treated with cardiotropic phosphodiesterase (PDE)-3 inhibitors. To understand the mechanism of the onset of this complication, we focused on the effects of various PDE-3 inhibitors and its stable metabolite of acetylamrinone on platelet aggregation occurring under physiological shear stress conditions.
Blood specimens were obtained from eight apparently healthy adult donors. Platelet-rich plasma was separated after anticoagulation by citrate. The effects of PDE-3 inhibitors of amrinone and olprinone, as well as the stable metabolite of the former of acetylamrinone, on platelet aggregation induced by its exposure to a shear rate of 1200 and 10,800 s(-1) were determined by optically modified cone-plate viscometer.
Both olprinone and amrinone inhibited platelet aggregation at 10,800 s(-1) in a dose-dependent manner with the IC(50) value of 14 +/- 1 and 61 +/- 8 microM (mean +/- S.D.), respectively, while amrinone significantly inhibited platelet aggregation at 1200 s(-1) only at highest concentration tested (100 microM). Contrary to the effects shown with PDE-3 inhibitors, acetylamrinone did not inhibit platelet aggregation at all. Moreover, it even enhanced the aggregation at 1200 s(-1) when used with 5 microM.
Our results demonstrate possible contribution of the enhancing effects of acetylamrinone on platelet aggregation occurring under blood flow conditions, which reduced the platelet count when occurring in real circulation, to the higher incidence of thrombocytopenia in patients treated with amrinone.
No preview · Article · Feb 2003 · Thrombosis Research
[Show abstract][Hide abstract] ABSTRACT: Platelets, which can adhere to damaged vascular surfaces and release bioactive substances upon activation, may play important roles in regulating local inflammatory responses. We focused on the surface translocation of CD40 ligand (CD40L) molecules when the platelets are exposed to a high shear stress.
Blood specimens were obtained from eight apparently healthy adult donors. The number of CD40L molecules appearing on the surface of platelets after exposure of platelet-rich plasma to a shear rate of 10,800 s(-1) was determined by quantitative flow cytometry.
The number of anti-CD40L IgG molecules bound per platelet increased from 15+/-80/platelet before to 355+/-122/platelet after exposure of the platelets to a shear rate of 10,800 s(-1) (p<0.01), but not after their exposure to the relatively low shear rate of 1200 s(-1). This shear-induced platelet surface translocation of CD40L, mediated by the von Willebrand factor (VWF)-GP Ibalpha interaction, was enhanced in the presence of a low concentration of epinephrine (100 nM), which by itself, however, could not cause platelet activation. Our results demonstrate that fluid force induces the appearance of CD40L on the surface of platelets, and also that this phenomenon is enhanced in the presence of a low concentration of epinephrine, corresponding to that released by sympathetic stimulation.
No preview · Article · Dec 2002 · Thrombosis Research
[Show abstract][Hide abstract] ABSTRACT: Biventricular pacing may be valuable for the treatment of patients with intractable heart failure, but how many patients in Japan would benefit from this type of therapy remains uncertain. This study investigated the incidence of intraventricular conduction delay in the electrocardiogram(ECG) as a marker of the need for biventricular pacing, as well as the underlying etiology of heart failure in patients admitted with congestive heart failure.
Patients with heart failure admitted to the Tokai University Hospital from January 1990 to September 2000 were studied retrospectively. The distribution of age, sex and underlying diseases, and that of the rhythm and the QRS width in ECG recordings were analyzed. Patients with a QRS width of over 121 msec in the ECG were classified as the 'wide QRS' group.
Of a series of 1,200 consecutive patients with heart failure, 872 patients, 499 males and 373 females (mean age 67.9 +/- 13.9 years) were admitted to the hospital and 71 had 'wide QRS' by ECG. Among those in the 'wide QRS' group, 37% had ischemic heart disease and 14% had dilated cardiomyopathy. The widest QRS complexes were encountered in patients with dilated cardiomyopathy and the largest number of wide QRS complexes was encountered in patients with ischemic heart disease.
The most frequent causes of heart failure among patients considered suitable for biventricular pacing were ischemic heart disease and dilated cardiomyopathy, which is consistent with previous reports. Compared with the statistics reported from western countries, the incidence of ischemic heart disease and the incidence of intraventricular conduction delay were lower in Japanese patients with heart failure. The incidence of intraventricular conduction delay among patients with heart failure was 8.6%. Therefore, fewer patients need biventricular pacing in Japan than in western countries. Nevertheless, patients with heart failure resistant to other therapies might still benefit from this type of therapy.
No preview · Article · Oct 2002 · Journal of Cardiology
[Show abstract][Hide abstract] ABSTRACT: We studied the role of glycoprotein (GP) VI in platelet adhesion and thrombus formation on the immobilized collagen and von Willebrand factor (vWF) surface under flow conditions.
Whole blood obtained from 2 patients with GP VI-deficient platelets and the effects of the Fab of anti-GP VI antibody (Fab/anti-GP VI) were tested. Blood containing platelets rendered fluorescent by mepacrine was perfused on immobilized type I collagen or vWF under controlled wall shear rate. Platelet adhesion and thrombus formation were detected by epifluorescent videomicroscopy. The percentage of surface coverage by the platelets was calculated. Fc receptor gamma-chain and spleen tyrosine kinase (Syk) were immunoprecipitated from the lysate of platelets stimulated by vWF plus ristocetin and then analyzed by antiphosphotyrosine immunoblotting. No platelet attachment was seen on the surface of collagen even after 9 minutes of perfusion of blood at relatively low (100 s(-1)) or high (1500 s(-1)) wall shear rate, either in the case of blood containing GP VI-deficient platelets or in the presence of Fab/anti-GP VI, whereas significant platelet thrombus formation was noted after control blood perfusion. Such interference with the actions of GP VI also reduced firm platelet adhesion on immobilized vWF. vWF-induced tyrosine phosphorylation of GP VI-associated Fc receptor gamma-chain followed by Syk activation occurred in normal platelets, but little activation of Syk occurred in GP VI-deficient platelets.
GP VI plays crucial roles in platelet thrombus formation on the surface of collagen under flow conditions in humans and is also involved in the process of firm platelet adhesion on the surface of vWF.
[Show abstract][Hide abstract] ABSTRACT: Factors influencing platelet accumulation around stents were to be investigated by an ex vivo flow chamber system.
Platelet accumulations on collagen surfaces under flow conditions were augmented in the presence of stents, especially at sites downstream from coil stents. Densitometric analysis revealed that 4.9+/-0.8 times more platelets accumulated downstream from coil stents than were formed downstream from tube stents (P<0.01), suggesting that stent morphology is an important determinant factor of its thrombogenicity. Platelet accumulations around stents were significantly inhibited by a combination of ticlopidine and aspirin, whereas aspirin alone produced only modest inhibition. Anti-glycoprotein IIb/IIIa (abciximab) inhibited platelet accumulation around stents in a dose-dependent manner, whereas the antibody blocking von Willebrand factor binding to glycoprotein Ib(alpha), which had been shown to inhibit platelet thrombus formation under high shear rates, did not inhibit the accumulation downstream from the coil stents. Our results suggest that the important characteristics of in vivo stent thrombosis, ie, augmented platelet accumulation with coil stents and the strong antithrombotic effect of the combination antiplatelet agents and an anti-glycoprotein IIb/IIIa, can be reproduced in ex vivo perfusion model.
We conclude that an ex vivo perfusion system is useful in the assessment of the thrombogenicity of various stents and in the screening of effective antiplatelet agents.
Full-text · Article · Aug 2002 · Arteriosclerosis Thrombosis and Vascular Biology
[Show abstract][Hide abstract] ABSTRACT: We investigated the effect of apolipoprotein E phenotype on changes in plasma levels of lipids and apoproteins by plant stanol ester (PSE) ingestion in Japanese subjects whose diet is low in fat and cholesterol.
The effect of PSE-containing spread was studied in a randomized, placebo-controlled trial. One hundred five healthy volunteers were enrolled for this study. Apolipoprotein E phenotyping was done in 96 of 105 subjects. We compared plasma levels at the start and end of the test period (4 wk). The daily ingestion of 2 g of plant stanols from the PSE spread significantly reduced plasma levels of low-density lipoprotein cholesterol by 8.9 +/- 6.6% (mean +/- standard deviation) in the E(3) group and 10.4 +/- 8.0% in the E(4) group. The daily ingestion of 2 g of plant stanols from the PSE spread significantly decreased plasma levels of apoprotein B by 5.4 +/- 7.9% in the E(3) group and 8.9 +/- 7.0% in the E(4) group. No further reductions of low-density lipoprotein cholesterol and apoprotein B were observed with 3 g/d of plant stanols from the PSE spread.
The ingestion of PSE spread significantly reduced plasma levels of total cholesterol, low-density lipoprotein cholesterol, and apoprotein B. However, the response to PSE ingestion was not influenced by apolipoprotein E phenotype.
[Show abstract][Hide abstract] ABSTRACT: The role of the adenosine 5'-diphosphate receptor P2Y(12) in platelet activation initiated by the von Willebrand factor (VWF)-GP Ibalpha interaction under high shear rate was investigated.
Blood samples were obtained from 11 donors. Shear-induced platelet aggregation was detected by optically modified cone-plate viscometer. Shear-induced VWF binding, P-selectin expression, and microparticle release were detected by flow cytometry. Platelet interaction with immobilized VWF was also investigated by parallel-plate flow chamber equipped with epifluorescent videomicroscopy. Effects of a selective P2Y(12) antagonist AR-C69931 MX were tested. AR-C69931 MX inhibited shear-induced platelet aggregation in a dose-dependent manner, achieving the maximum inhibition at 100 nmol/L. The extent of aggregation after exposure to a shear rate of 10 800 s(-1) for 6 minutes in the presence of 100 nmol/L AR-C69931 MX was 32.4+/-8.2% (mean+/-SD), which was significantly lower than the value in the controls of 69.7+/-9.6% (P<0.01). The inhibiting effects of AR-C69931 MX were reversed by exogenous addition of adenosine 5'-diphosphate. Shear-induced VWF binding and P-selectin surface translocation, which occurred in 4696+/-911 and 5964+/-784, respectively, of 10 000 measured platelets, was also inhibited by AR-C69931 MX (100 nmol/L) to 1948+/-528 and 2797+/-718, respectively (P=0.0018 and P=0.0009). Microparticle release was similarly inhibited. In a flow chamber experiment, firm platelet attachment on immobilized VWF was inhibited by AR-C69931 MX, whereas transient interaction was not influenced. All the above reactions were completely inhibited by blocking VWF-GP Ibalpha interaction.
We have demonstrated that the stimulation of P2Y(12) is involved in platelet activation initiated by the binding of VWF to GP Ibalpha induced by a high shear rate.
[Show abstract][Hide abstract] ABSTRACT: We report the estimation of left ventricular systolic pressure (LVSP) by a left ventricular (LV) volume-time curve obtained from electrocardiogram (ECG) gated 99mTc-tetrofosmin single photon emission computed tomography (SPECT) using quantitative gated SPECT (QGS). LVSP was calculated based on the following parameters: LV volumes, velocity and acceleration of LV contraction, aortic valve area and density of blood. The first three parameters can be derived from ECG gated SPECT. In 16 patients, the LV volume-time curve was obtained from ECG gated SPECT by using QGS. LVSP was estimated by the above-mentioned theory. The values of estimated peak LVSP were compared with those measured from a pressure transducer. There was a correlation between the values of peak LVSP estimated by the LV volume-time curve and those measured by pressure transducer (r=0.69, P<0.01). Using QGS, LVSP and the systolic LV pressure-volume relationship could be estimated by the LV volume-time curve.
No preview · Article · Feb 2002 · Nuclear Medicine Communications
[Show abstract][Hide abstract] ABSTRACT: Ticlopidine, recently classified as a P2Y(12) ADP receptor blockade, is known to be an effective antiplatelet agent preventing arterial thrombosis, e.g., myocardial infarction or cerebral infarction, but the mechanism of the in vivo antithrombotic effects of ticlopidine is not fully understood. Blood was drawn from seven normal volunteers before and 7 days after consecutive intake of ticlopidine, and 1 day after oral intake of aspirin after 7 days of ticlopidine wash-out period. Effects of drug intake on shear-induced von Willebrand factor (vWF) binding to platelets, platelet activation evidenced by P-selectin surface expression and translocation of GP Ibalpha, and vWF-mediated platelet aggregation, were investigated by using an optically modified cone-plate viscometer and quantitative flow cytometry. The maximum extent of platelet aggregation occurring under a high shear rate of 10800 s(-1), presumably mediated by vWF, was not significantly influenced by either ticlopidine or aspirin. However, significant dissociation of once aggregated platelets occurred in samples obtained after ticlopidine intake (25.4 +/- 9.3%, P = 0.00030) and less significantly after aspirin intake (15.9 +/- 5.7%, P = 0.0013), while only insignificant and modest dissociation occurred in controls (6.3 +/- 4.4%, n.s.). Binding experiments also revealed that the shear-induced vWF binding to platelets was significantly inhibited by ticlopidine, and less significantly by aspirin, although other indicators of platelet activation, such as shear-induced P-selectin expression and GP Ibalpha translocation were not influenced by either ticlopidine or aspirin. We demonstrate here that platelet aggregation mediated by von Willebrand factor (vWF) under a high shear rate of 10800 s(-1) cannot be stabilized and that dissociation occurs readily when ADP receptor stimulation is blocked by continuous intake of ticlopidine, indicating that these effects on platelet thrombus formation may contribute to the in vivo antithrombotic effects of ticlopidine.