Ticlopidine Selectively Inhibits Human Platelet Responses to Adenosine Diphosphate

SummaryPlatelet aggregation and fibrinogen binding were studied in 15 individuals before and 7 days after the oral administration of ticlopidine (250 mg b.i.d.). Ticlopidine significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), the endoperoxide analogue U46619, collagen or low concentrations of thrombin, but did not inhibit platelet aggregation induced by epinephrine or high concentrations of thrombin. Ticlopidine inhibited 125I-fibrinogen binding induced by ADP, U46619 or thrombin (1 U/ml). The ADP scavengers apyrase or CP/CPK, added in vitro to platelet suspensions obtained before ticlopidine, caused the same pattern of aggregation and 125I-fibrihogen binding inhibition as did ticlopidine. Ticlopidine did not inhibit further platelet aggregation and 125I-fibrinogen binding induced in the presence of ADP scavengers. After ticlopidine administration, thrombin or U46619, but not ADP, increased the binding rate of the anti-GPIIb/IIIa monoclonal antibody 7E3 to platelets. Ticlopidine inhibited clot retraction induced by reptilase plus ADP, but not that induced by thrombin or by reptilase plus epinephrine, and prevented the inhibitory effect of ADP, but not that of epinephrine, on the PGE1-induced increase in platelet cyclic AMP. The number of high- and low-affinity binding sites for 3H-ADP on formalin-fixed platelets and their K d were not modified by ticlopidine. These findings indicate that ticlopidine selectively inhibits platelet responses to ADP.

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Inhibition of Platelet Function by Antiarrhythmic Drugs, Verapamil and Disopyramide

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657151 ◽

1982 ◽

Vol 47 (02) ◽

pp. 150-153 ◽

Cited By ~ 13

Author(s):

P Han ◽

C Boatwright ◽

N G Ardlie

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Antiarrhythmic Drugs ◽

Adenosine Diphosphate ◽

Inhibitory Effect ◽

Second Phase ◽

Ionophore A23187 ◽

High Concentrations ◽

Artery Disease

SummaryVarious cardiovascular drugs such as nitrates and propranolol, used in the treatment of coronary artery disease have been shown to have an antiplatelet effect. We have studied the in vitro effects of two antiarrhythmic drugs, verapamil and disopyramide, and have shown their inhibitory effect on platelet function. Verapamil, a calcium channel blocker, inhibited the second phase of platelet aggregation induced by adenosine diphosphate (ADP) and inhibited aggregation induced by collagen. Disopyramide similarly inhibited the second phase of platelet aggregation caused by ADP and aggregation induced by collagen. Either drug in synergism with propranolol inhibited ADP or collagen-induced platelet aggregation. Disopyramide at high concentrations inhibited arachidonic add whereas verapamil was without effect. Verapamil, but not disopyramide, inhibited aggregation induced by the ionophore A23187.

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In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646570 ◽

1989 ◽

Vol 61 (02) ◽

pp. 254-258 ◽

Cited By ~ 21

Author(s):

Margaret L Rand ◽

Peter L Gross ◽

Donna M Jakowec ◽

Marian A Packham ◽

J Fraser Mustard

Keyword(s):

Cyclic Amp ◽

Inhibitory Effect ◽

Rabbit Platelet ◽

Inhibitory Effects ◽

Low Concentrations ◽

Rabbit Platelets ◽

High Concentrations ◽

In Vitro Effects ◽

Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

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Functional Involvement of Thrombospondin in Platelet Aggregation Induced by Low Versus High Concentrations of Thrombin

Thrombosis and Haemostasis ◽

10.1055/s-0038-1661464 ◽

1986 ◽

Vol 55 (01) ◽

pp. 136-142 ◽

Cited By ~ 4

Author(s):

K J Kao ◽

David M Shaut ◽

Paul A Klein

Keyword(s):

Platelet Aggregation ◽

Binding Sites ◽

Inhibitory Effect ◽

Activated Platelets ◽

Low Concentrations ◽

Platelet Binding ◽

Functional Involvement ◽

Thrombin Activation ◽

Platelet Aggregates ◽

High Concentrations

SummaryThrombospondin (TSP) is a major platelet secretory glycoprotein. Earlier studies of various investigators demonstrated that TSP is the endogenous platelet lectin and is responsible for the hemagglutinating activity expressed on formaldehyde-fixed thrombin-treated platelets. The direct effect of highly purified TSP on thrombin-induced platelet aggregation was studied. It was observed that aggregation of gel-filtered platelets induced by low concentrations of thrombin (≤0.05 U/ml) was progressively inhibited by increasing concentrations of exogenous TSP (≥60 μg/ml). However, inhibition of platelet aggregation by TSP was not observed when higher than 0.1 U/ml thrombin was used to activate platelets. To exclude the possibility that TSP inhibits platelet aggregation by affecting thrombin activation of platelets, three different approaches were utilized. First, by using a chromogenic substrate assay it was shown that TSP does not inhibit the proteolytic activity of thrombin. Second, thromboxane B2 synthesis by thrombin-stimulated platelets was not affected by exogenous TSP. Finally, electron microscopy of thrombin-induced platelet aggregates showed that platelets were activated by thrombin regardless of the presence or absence of exogenous TSP. The results indicate that high concentrations of exogenous TSP (≥60 μg/ml) directly interfere with interplatelet recognition among thrombin-activated platelets. This inhibitory effect of TSP can be neutralized by anti-TSP Fab. In addition, anti-TSP Fab directly inhibits platelet aggregation induced by a low (0.02 U/ml) but not by a high (0.1 U/ml) concentration of thrombin. In conclusion, our findings demonstrate that TSP is functionally important for platelet aggregation induced by low (≤0.05 U/ml) but not high (≥0.1 U/ml) concentrations of thrombin. High concentrations of exogenous TSP may univalently saturate all its platelet binding sites consequently interfering with TSP-crosslinking of thrombin-activated platelets.

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Thiosulfinates Inhibit Platelet Aggregation and Microparticle Shedding at a Calpain-dependent Step

Thrombosis and Haemostasis ◽

10.1055/s-0037-1616063 ◽

2001 ◽

Vol 86 (11) ◽

pp. 1284-1291 ◽

Cited By ~ 16

Author(s):

Brigitte Brohard-Bohn ◽

Sabine Pain ◽

Christilla Bachelot-Loza ◽

Jacques Auger ◽

Francine Rendu

Keyword(s):

Platelet Aggregation ◽

Annexin V ◽

Inhibitory Effect ◽

Inhibit Platelet Aggregation ◽

Clot Retraction ◽

Allium Species ◽

Calpain Activation ◽

Fibrinogen Binding ◽

Ic50 Values ◽

Dose Dependent

SummaryThiosulfinates (TSs) are sulfur compounds generated through the processing of different Allium species with antiplatelet property. To further define this platelet inhibitory effect we studied diallyl-TS (Al2TS), dipropyl-TS (Pr2TS), and dimethyl-TS (Me2TS) on platelet responses. The three TSs inhibited dose-dependent platelet aggregation, with IC50 values of 15 ± 2, 19 ± 2, and 9 ± 1 μM for Al2TS, Pr2TS and Me2TS, respectively. TSs had no effect on the expression of a platelet procoagulant surface, measured by flow cytometry as the binding of annexin V-FITC. They inhibited the microparticle shedding and clot retraction. Since the microparticle shedding is a calpain-activation dependent step, we assessed calpain activation by analysis of autoproteolysis in shorter active forms and by talin proteolysis in the presence of TSs. Calpain activation was inhibited by TSs independently of fibrinogen binding. Thus, TSs represent a new category of platelet inhibitors, acting on cal-pain-induced events.

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Randomized, Placebo-controlled, Blinded and Cross-matched Study on the Antiplatelet Effect of Inhaled Nitric Oxide in Healthy Volunteers

Thrombosis and Haemostasis ◽

10.1055/s-0037-1613804 ◽

2000 ◽

Vol 83 (02) ◽

pp. 309-315 ◽

Cited By ~ 27

Author(s):

Axel Herr ◽

Johann Motsch ◽

Alexandra Holzmann ◽

Jörg Weimann ◽

Friedemann Taut ◽

...

Keyword(s):

Nitric Oxide ◽

Platelet Aggregation ◽

Healthy Volunteers ◽

Bleeding Time ◽

Inhibitory Effect ◽

Inhaled Nitric Oxide ◽

Men And Women ◽

Fibrinogen Binding ◽

Matched Study

SummaryThe platelet inhibitory effect of 0-40 ppm inhaled nitric oxide (NO) was investigated in healthy men and women. In both groups, ADPand collagen-induced platelet aggregation was significantly inhibited 20 (T20) and 40 min (T40) after the beginning of inhalation of 5, 10, and 40 ppm. Moreover, in both men and women, the in vitro bleeding time was significantly prolonged at T20 and T40 during inhalation of 40 ppm. Inhalation of NO also inhibited P-selectin expression at 5, 10, and 40 ppm and fibrinogen binding to the GPIIb/IIIa-receptor at 40 ppm. In conclusion, in healthy volunteers, the platelet inhibitory effect of inhaled NO was not dose-related, since it was significant at 5 and 10 ppm but did not increase during the administration of higher NO concentrations. In addition, gender-related differences were only observed in ADP-induced platelet aggregation at 10 ppm and in bleeding time prolongation at 40 ppm.

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Effects of OKM5, a monoclonal antibody to glycoprotein IV, on platelet aggregation and thrombospondin surface expression [see comments]

Blood ◽

10.1182/blood.v76.12.2501.bloodjournal76122501 ◽

1990 ◽

Vol 76 (12) ◽

pp. 2501-2509 ◽

Cited By ~ 1

Author(s):

ML Aiken ◽

MH Ginsberg ◽

V Byers-Ward ◽

EF Plow

Keyword(s):

Monoclonal Antibody ◽

Platelet Aggregation ◽

Membrane Protein ◽

Adenosine Diphosphate ◽

Surface Expression ◽

Inhibitory Effect ◽

Target Antigen ◽

Functional Responses ◽

Fibrinogen Binding ◽

Intact Antibody

The monoclonal antibody, OKM5, recognizes an 88-Kd monocyte membrane protein and also binds to the platelet membrane protein, GPIV (GPIIIb, CD36). In this study, we have found that the OKM5 target epitope is present at approximately 12,000 copies per platelet and that interaction with the antibody has both stimulatory and inhibitory effects on platelet function. In the absence of other stimuli, OKM5 induced platelet aggregation, secretion, and expression of fibrinogen receptors. These stimulatory responses required intact antibody as F(ab')2 fragments were not active but blocked the stimulatory activity of the intact antibody. In contrast, exposure of platelets to OKM5 followed by another strong stimulus such as thrombin resulted in a marked suppression of fibrinogen, fibronectin, and von Willebrand factor binding to the cells. This effect was not noted when a weak stimulus, adenosine diphosphate, was the second agonist. At OKM5 concentrations that interfered with fibrinogen binding to thrombin- stimulated platelets by 80% to 90%, platelet binding of exogenous thrombospondin, or surface expression of endogenous thrombospondin was not affected. The inhibitory effect of OKM5 on fibrinogen binding to thrombin-stimulated platelets was related to the formation of massive platelet aggregates in the samples. These results show that interaction of OKM5 with its target antigen on platelets can elicit diverse functional responses from the cells.

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Effect of aluminium toxicity on the development of poplar (Populus tremula L. x P. alba L.) cultured in vitro

Acta Societatis Botanicorum Poloniae ◽

10.5586/asbp.1999.032 ◽

2014 ◽

Vol 68 (4) ◽

pp. 245-250 ◽

Cited By ~ 1

Author(s):

Krystyna Bojarczuk

Keyword(s):

Aluminium Toxicity ◽

Inhibitory Effect ◽

Populus Tremula ◽

Aluminium Chloride ◽

Adventitious Bud ◽

Aluminium Sulphate ◽

Low Concentrations ◽

The Media ◽

High Concentrations

Adventitious bud cultures were established using vegetative buds from selected clones of poplar (Populus tremula L. x P. alba L.) as initial explants. For multiplication of shoots a modified Murashige and Skoog medium (MS) was used. Aluminium salts (aluminium sulphate and aluminium chloride) were added to the media. It was found that the pH of the medium had no effect on the development of cultures at low concentrations of nutrients (1/2 or 1/4 MS). Low concentrations of aluminium (Al 25mg•dm-3 supplied as aluminium sulphate, Al 15 mg•dm-3 as aluminium chloride) had no inhibitory effect on shoot development but decreased regeneration of adventitious roots. High concentrations of aluminium inhibited the development of shoots and roots, especially in a medium at pH 4.5. Microcuttings rooted in the highest percentage and formed the strongest rooting system on 1/4 strength MS medium at pH 4.5. It was found that there was no difference between the rooting of shoots excised from cultures cultivated with or without A1 in this medium at pH 5.5.

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Effect of Low Concentrations of Prostacyclin on Platelet Function in Vitro

Anaesthesia and Intensive Care ◽

10.1177/0310057x9702500402 ◽

1997 ◽

Vol 25 (4) ◽

pp. 343-346 ◽

Cited By ~ 13

Author(s):

P. V. Van Heerden ◽

N. M. Gibbs ◽

N. Michalopoulos

Keyword(s):

Platelet Aggregation ◽

Entire Range ◽

Venous Blood ◽

Maximum Amplitude ◽

Adenosine Diphosphate ◽

Systemic Circulation ◽

Direct Effects ◽

Low Concentrations ◽

Platelet Aggregation Defect

The study was performed to determine the possible direct effects of low concentrations of prostacyclin that might spill over into the systemic circulation during the administration of inhaled aerosolized prostacyclin. Platelet aggregation in response to adenosine diphosphate and collagen, as well as measurement of the maximum amplitude of the thrombelastograph (TEG), was undertaken in vitro using venous blood exposed to low concentrations of prostacyclin (0, 10, 100 and 500 pg/ml) from eight healthy volunteers. There were statistically significant reductions in parameters of platelet aggregation in response to the agonists adenosine diphosphate (1 μmol/l and 8 μmol/l) and collagen (10 μmol/l) following exposure to as little as 10 pg/ml of prostacyclin. The maximum amplitude of the TEG was unchanged over the entire range of prostacyclin concentrations studied. The results indicate that low concentrations of prostacyclin or prostacyclin metabolite such as may be observed during inhaled aerosolized prostacyclin therapy are likely to be associated with a marked platelet aggregation defect. This defect was not detected by the TEG.

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Hematin: unique effects of hemostasis

Blood ◽

10.1182/blood.v61.2.243.bloodjournal612243 ◽

1983 ◽

Vol 61 (2) ◽

pp. 243-249

Author(s):

R Glueck ◽

D Green ◽

I Cohen ◽

CH Ts'ao

Keyword(s):

Platelet Aggregation ◽

Blood Cell ◽

Adenosine Triphosphate ◽

Antithrombin Iii ◽

Degradation Products ◽

Acute Intermittent Porphyria ◽

Adenosine Diphosphate ◽

Adp Release ◽

Formalin Fixed

Hematin is clinically useful in the treatment of acute intermittent porphyria. Recently, hematin-induced coagulopathy has been reported, and a patient we treated bled during hematin therapy. On 3 separate occasions, infusions of hematin (4 mg/kg) induced thrombocytopenia, prolongation of the prothrombin time, partial thromboplastin time. Reptilase time, and apparent decreases in fibrinogen and increases in fibrin(ogen) degradation products (FDP). However, fibrinogen assayed by heat precipitation was unchanged, the protamine paracoagulation test was negative, there was no red blood cell fragmentation, and plasminogen and antithrombin III remained normal, excluding the presence of disseminated intravascular coagulation. Furthermore, premedication with heparin, 5000 U i.v., failed to prevent the lengthening of the Reptilase time and exacerbated the thrombocytopenia. In vitro studies revealed that hematin, 0.1 mg/ml, aggregated platelets and induced the release of 14C-serotonin and adenosine triphosphate (ATP). Hematin also aggregated washed or gel-filtered platelets but had no effect on formalin-fixed platelets. Aggregation was inhibited by aspirin (0.12 mg/ml), adenosine triphosphate, and apyrase, suggesting that hematin aggregated platelets by inducing adenosine diphosphate (ADP) release. Hematin (0.07 mg/ml) progressively inactivated thrombin and 0.1 mg/ml prolonged the Reptilase time. Thus, hematin is unique in that it both induces platelet aggregation and inhibits coagulation.

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Potentiation of Adrenaline-Induced Platelet Aggregation by Angiotensin II

Thrombosis and Haemostasis ◽

10.1055/s-0038-1660105 ◽

1985 ◽

Vol 54 (03) ◽

pp. 717-720 ◽

Cited By ~ 32

Author(s):

Yu-An Ding ◽

D Euan MacIntyre ◽

Christopher J Kenyon ◽

Peter F Semple

Keyword(s):

Platelet Aggregation ◽

Angiotensin Ii ◽

Human Platelet ◽

Inhibitory Effect ◽

Facilitatory Effect ◽

Ang Ii ◽

Human Platelet Aggregation ◽

Low Concentrations ◽

High Concentrations ◽

Stimulation Of

SummaryThe effects of angiotensin II (ANG II) alone and in combination with other agonists on human platelet aggregation, thromboxane B2 (TxB2) and cytosolic [Ca2+]i were investigated. ANG II (10™11 - 10™7 M) alone had no direct effect on aggregation, TxB2 production or [Ca2+]i after short- (<2 min) or longterm (30 min) incubation. In contrast, low concentrations of ANG II (10™11 M) enhanced adrenaline-induced platelet aggregation but high concentrations (10™7 M) had an inhibitory effect. Moreover, ANG II (10™11 - 10™7 M) augmented platelet responses to the TxA2 mimetic, U44069. Pretreatment of platelets with flurbiprofen abolished this facilitatory effect of ANG II on adrenaline- but not on U44069-induced platelet aggregation. These results suggest that ANG II stimulation of agonist-induced platelet activation may be due to potentiation of the effects rather than the synthesis of TxA2

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