Interaction between ATP and catecholamines in stimulation of platelet aggregation

Platelets, on activation by endothelial damage, release ADP, ATP, serotonin, epinephrine, and norepinephrine. Although ATP is known to augment the action of norepinephrine in cardiovascular and endocrine systems, the possible interaction between ATP and catecholamines in regulation of platelet reactivity has not been reported. The addition of ATP (1–5 μM) to human platelet-rich plasma did not induce platelet aggregation; however, it selectively augmented the aggregatory response to norepinephrine and epinephrine, but not to serotonin. This potentiating action of ATP was dose dependent and was not due to contamination by, or hydrolysis to, ADP. The action of ATP was blocked by 10 μM of adenosine 3′-phosphate 5′-phosphosulfate, a selective P2Y1receptor antagonist. ATP alone did not cause release of intracellular Ca2+, but produced a significant Ca2+response in the presence of norepinephrine. In contrast, the P2X1receptor agonists P1,P6-diadenosine-5′ hexophosphate and α,β-methylene-ATP had no effect on norepinephrine-induced platelet aggregation even when added at 100 μM. This synergistic interaction between ATP and norepinephrine in stimulating platelet aggregation may have significant clinical implications and suggests a prothrombotic role for ATP in stress.

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Endotoxin-Induced Platelet Activation in Human Whole Blood In Vitro

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647499 ◽

1988 ◽

Vol 59 (03) ◽

pp. 378-382 ◽

Cited By ~ 11

Author(s):

Gyorgy Csako ◽

Eva A Suba ◽

Ronald J Elin

Keyword(s):

Platelet Aggregation ◽

Whole Blood ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Atp Release ◽

Human Platelets ◽

Lag Phase ◽

Human Whole Blood ◽

Dose Dependent

SummaryThe effect of purified bacterial endotoxin was studied on human platelets in vitro. In adding up to 1 μg/mL of a highly purified endotoxin, we found neither aggregation nor ATP release in heparinized or citrated human platelet-rich plasma. On the other hand, endotoxin at concentrations as low as a few ng/mL (as may be found in septic patients) caused platelet aggregation in both heparinized and citrated human whole blood, as monitored by change in impedance, free platelet count, and size. Unlike collagen, the platelet aggregation with endotoxin occurred after a long lag phase, developed slowly, and was rarely coupled with measurable release of ATP. The platelet aggregating effect of endotoxin was dose-dependent and modified by exposure of the endotoxin to ionizing radiation. Thus, the activation of human platelets by “solubilized” endotoxin in plasma requires the presence of other blood cells. We propose that the platelet effect is mediated by monocytes and/or neutrophils stimulated by endotoxin.

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Comparisons of Biochemical and Pharmacological Properties of Prostacyclins with Modified ω-Side Chain

10.1055/s-0038-1665820 ◽

1979 ◽

Author(s):

K. U. Weithmann ◽

W. Bartmann ◽

G. Beck ◽

U. Lerch ◽

E. Konz ◽

...

Keyword(s):

Platelet Aggregation ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Systemic Blood Pressure ◽

Side Chain ◽

Adenylate Cyclase System ◽

Dependent Manner ◽

High Biological Activity ◽

Structure Activity ◽

Dose Dependent

PGI2-analogs in which the n-pentyl moiety in position 15 was replaced by several residues, were subjected to structure-activity studies. Some of the modified PGI2’s showed remarkable potency in regard to antiplatelet and vasodilator actions. in order to evaluate these potencies the inhibition of arachidonic acid induced platelet aggregation in human platelet rich plasma, relaxation of bovine coronary artery (BCA) and systemic blood pressure (BP) in the anesthetized rat were determined. Platelet aggregation was inhibited by PGI2 with an IC50 approx. 3-10-9M, BP was decreased in a dose dependent manner with an ED25, of 0.23 ug/kg i.v. and a marked relaxation of BCA was observed. Similar results were obtained with PGI2-methylester. Substitution of the n-pentyl moiety by cyclohexyl, 3-furyl-2-ethyl or 3-thienyl-oxymethyl resulted in PGI2- and PGI2-methyl-ester-analogs with high biological activity, whereas substitution by T6,16-dimethyl-18-oxa-alkyl or phenoxymethyl caused a loss of activity in the models used. The potency of the prostacyclins in the platelet model seem to depend upon their ability to elevate the platelet cyclo-AMP level. Thus the antiplatelet potency of modified PGI2’s may reflect their ability to affect the adenylate cyclase system.

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Comparisons of Biochemical and Pharmacological Properties of Prostacyclins with Modified ω-Side Chain

10.1055/s-0039-1684548 ◽

1979 ◽

Author(s):

K.U. Weithmann ◽

W. Bartmann ◽

G. Beck ◽

U. Lerch ◽

E. Konz ◽

...

Keyword(s):

Platelet Aggregation ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Systemic Blood Pressure ◽

Side Chain ◽

Adenylate Cyclase System ◽

Dependent Manner ◽

High Biological Activity ◽

Structure Activity ◽

Dose Dependent

PGI2-analogs in which the n-pentyl moiety in position IS was replaced by several residues, were subjected to structure-activity studies. Some of the modified PGI2’s showed remarkable potency in regard to antiplatelet and vasodilator actions. In order to evaluate these potencies the inhibition of arachidonic acid induced platelet aggregation in human platelet rich plasma, relaxation of bovine coronary artery (BCA) and systemic blood pressure (BP) in the anesthetized rat were determined. Platelet aggregation was inhibited by PGI2, with an IC50 approx. 3.10-9, BP was decreased in a dose dependent manner with an ED25 of 0.23 ug/kg i.v. and a marked relaxation of BCA was observed. Similar results were obtained with PGK-methylester. Substitution of the n-pentyl moiety by cyclohexyl, 3-furyl-2-ethyl or 3-thienyl-oxymethyl resulted in PGI2, and PGK2-methyl-ester-analogs with high biological activity, whereas substitution by 16, 16-dimethyl-18-oxa-alkyl or phcnoxymethyl caused a loss of activity in the models used. The potency of the prostacyclins in the platelet model seem to depend upon their ability to elevate the platelet cyclo-AMP level. Thus the antiplatelet potency of modified PGI2’s may reflect their ability to affect the adenylate cyclase system.

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13-Azaprostanoic Acid Potentiates Prostacyclin Induced Platelet Deaggregation

10.1055/s-0038-1652602 ◽

1981 ◽

Author(s):

L V Parise ◽

D Venton ◽

G C Le Breton

Keyword(s):

Platelet Aggregation ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Present Report ◽

The Other ◽

Calcium Sequestration ◽

Significant Difference ◽

Induced Aggregation ◽

Camp Levels ◽

Stimulation Of

13-Azaprostanoic acid (13-APA), a specific thromboxane/endoperoxide receptor antagonist, reverses platelet aggregation stimulated by the endoperoxide analog U46619. The present report demonstrates that 13-APA also potentiates prostacyclin (PGI2) reversal of U46619-induced aggregation. Human platelet rich plasma was aggregated with 3 × 106M U46619. Deaggregation was induced 2 min. sitosequent to the addition of aggregating agent and was measured over a 3 min. period. Concentrations of 13-APA (4 × 10-4M) and PGI2(4 × 10-9M) were chosen such that each agent individually induced approximately 20% deaggregation. Addition of half of the above concentrations of these agents i.e. 2 × 10-4M 13-APA plus 2 × 10-9M PGI2resulted in 62% deaggregation, demonstrating that the observed response was supraadditive. Only 8% deaggregation was induced by 2 × 10-4M 13-APA alone and 0% by 2 × 10-9M PGI2 alone. PGI2 causes platelet deaggregation presumably through elevation of cAMP. 13-APA, however, did not increase cAMP levels even at concentrations of 13-APA as high as 1.2 × 10-3M i.e. 9.8 ± 1.3 pmoles/ml for control and 10.8 ± 1.2 for 13-APA. Nevertheless it is possible that the observed potentiation of deaggregation was the result of 13-APA facilitating PGI2 stimulation of adenylate cyclase. Measurement of cAMP during deaggregation, however, showed no significant difference between treatment with PGI2 alone and treatment with PGI2 plus 13-APA i.e. 11.3 ± 0.4 pmoles/ml for control, 11.4 ± 0.3 pmoles/ml for 13-APA, 16.1 ± 0.5 pmoles/ml for PGI2 and 16.5 ± 0.8 pmoles/ml for PGI2 plus 13-APA. These results clearly establish that 13-APA and PGI2deaggregate platelets by distinctly separate mechanisms. In this regard we propose that PGI2 causes platelet deaggregation by stimulating intraplatelet calcium sequestration through a cAMP dependent process. 13-APA, on the other hand, blocks the ability of U46619 to mobilize intraplatelet calcium. The combination of these two mechanisms presumably results in the observed potentiation of deaggregation.

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Phospholipase C from Clostridium Perfringens Induces Human Platelet Aggregation in Plasma

Thrombosis and Haemostasis ◽

10.1055/s-0038-1642761 ◽

1988 ◽

Vol 59 (02) ◽

pp. 236-239 ◽

Cited By ~ 2

Author(s):

Giovanna Barzaghi ◽

Chiara Cerletti ◽

Giovanni de Gaetano

Keyword(s):

Platelet Aggregation ◽

Receptor Antagonist ◽

Phospholipase C ◽

Clostridium Perfringens ◽

Human Platelet ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Platelet Activating Factor ◽

Inhibitory Effect ◽

Thromboxane Receptor Antagonist

SummaryWe studied the aggregating effect of different concentrations of phospholipase C (PLC) (extracted from Clostridium perfringens) on human platelet-rich plasma (PRP). PRP was preincubated with PLC for 3 min at 37° C and the platelet aggregation was followed for 10 min. The threshold aggregating concentration (TAG) of PLC was 3-4 U/ml.We also studied the potentiation of PLC with other stimuli on platelet aggregation. Potentiating stimuli, such as arachidonic acid (AA), ADP. Platelet Activating Factor (PAF) and U-46619 (a stable analogue of cyclic endoperoxides) were all used at subthreshold concentrations. We also studied the possible inhibitory effect of aspirin, apyrase, TMQ, a prostaglandin endoper- oxide/thromboxane receptor antagonist and BN-52021, a PAF receptor antagonist. Only aspirin and apyrase were able to reduce aggregation induced by PLC alone and PLC + AA and PLC + ADP respectively. TMQ and BN-52021 were inactive. In ex vivo experiments oral aspirin (500 mg) partially inhibited platelet aggregation induced by PLC alone, PLC + AA and PLC + ADP 2 and 24 h after administration. Aspirin 20 mg for 7 days also reduced aggregation induced by PLC + AA.

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Inhibitory Effect of Staphylokinase on Platelet Aggregation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1649679 ◽

1993 ◽

Vol 70 (05) ◽

pp. 834-837 ◽

Cited By ~ 6

Author(s):

Akira Suehiro ◽

Yoshio Oura ◽

Motoo Ueda ◽

Eizo Kakishita

Keyword(s):

Platelet Aggregation ◽

Human Platelet ◽

Degradation Products ◽

Platelet Rich Plasma ◽

Inhibitory Effect ◽

Effective Concentration ◽

Inhibit Platelet Aggregation ◽

Platelet Suspension ◽

Washed Platelet ◽

Human Platelet Aggregation

SummaryWe investigated the effect of staphylokinase (SAK), which has specific thrombolytic properties, on human platelet aggregation. Platelet aggregation induced with collagen was observed following preincubation of platelets in platelet-rich plasma (PRP) or washed platelet suspension (WP) with SAK at 37° C for 30 min. SAK inhibited platelet aggregation in PRP only at the highest examined concentration (1 x 10-4 g/ml). Although SAK did not inhibit platelet aggregation in WP which contained fibrinogen, it did when the platelets had been preincubated with SAK and plasminogen. The most effective concentration in WP was 1 x 10-6 g/ml. The effect could be inhibited by adding aprotinin or α2-antiplasmin. The highest generation of plasmin in the same preincubation fluid was detected at 1 x 10-6 g/ml SAK. We concluded that SAK can inhibit platelet aggregation in WP by generating plasmin and/or fibrinogen degradation products, but is only partially effective in PRP because of the existence of α2-antiplasmin.

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Stimulated Platelet Aggregation, Thromboxane B2 Formation and Platelet Sensitivity to Prostacyclin - A Critical Evaluation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650170 ◽

1981 ◽

Vol 45 (03) ◽

pp. 204-207 ◽

Cited By ~ 42

Author(s):

Wolfgang Siess ◽

Peter Roth ◽

Peter C Weber

Keyword(s):

Arachidonic Acid ◽

Platelet Count ◽

Platelet Aggregation ◽

Reliable Method ◽

Platelet Rich Plasma ◽

Critical Evaluation ◽

Vascular Diseases ◽

Thromboxane B2 ◽

Test Time ◽

Stimulation Of

SummaryPlatelets have been implicated in the development of atherosclerotic and thrombotic vascular diseases. Evaluation of platelet aggregation in relation to endogenously formed compounds which affect platelet function may provide information of clinical and pharmacological relevance. We describe a method in which thromboxane B2 (TXB2) formation was analyzed following stimulation of platelet-rich plasma (PRP) with ADP, 1-epinephrine, collagen, and arachidonic acid. In addition, we determined platelet sensitivity to prostacyclin following ADP- and collagen-induced platelet aggregation. The parameters under study were found to depend on the platelet count in PRP, on the type and dose of the aggregating agent used, and on the test time after blood sampling. By standardization of these variables, a reliable method was established which can be used in clinical and pharmacological trials.

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A Physiologic Regulator of Collagen-Induced Platelet Aggregation: Inhibition by Clq

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650145 ◽

1981 ◽

Vol 45 (02) ◽

pp. 110-115 ◽

Cited By ~ 5

Author(s):

György Csákó ◽

Eva A Suba

Keyword(s):

Platelet Aggregation ◽

Human Platelet ◽

Platelet Reactivity ◽

High Specificity ◽

Turbidimetric Method ◽

Specific Manner ◽

Aggregation Inhibition ◽

Different Tissues

SummaryPlatelet aggregations were studied by a turbidimetric method in citrated human platelet-rich plasmas (PRP) in vitro. Human Clq inhibited the aggregations caused by collagens derived from different tissues and species. Clq was needed by weight in comparable quantities to collagen for neutralizing the aggregating effect. The dependence of the inhibitory reaction on the preincubation of platelets with Clq and the differences in the occurrence of aggregating substances in supernatants of PRP triggered with collagen in the presence or absence of Clq, confirmed that Clq exerts its effect by preventing fixation of collagen to platelets. In addition, the high specificity of the inhibitory action of Clq for collagen-induced platelet aggregation was demonstrated by results obtained for testing a variety of aggregating agents in combination with Clq and/or collagen.Since normal concentrations of Clq in the blood are in the range of inhibitory doses of Clq for collagen-induced platelet aggregations in vitro and upon activation of complement Clq is known to dissociate from Cl, it is proposed that Clq may participate in a highly specific manner in regulating platelet reactivity to collagen in vivo.

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Testosterone Potentiation of Ionophore and ADP Induced Platelet Aggregation : Relationship to Arachidonic Acid Metabolism

Thrombosis and Haemostasis ◽

10.1055/s-0038-1653405 ◽

1981 ◽

Vol 46 (02) ◽

pp. 538-542 ◽

Cited By ~ 42

Author(s):

R Pilo ◽

D Aharony ◽

A Raz

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Unsaturated Fatty Acids ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Arachidonic Acid Metabolism ◽

Ionophore A23187 ◽

Low Concentrations ◽

Induced Aggregation

SummaryThe role of arachidonic acid oxygenated products in human platelet aggregation induced by the ionophore A23187 was investigated. The ionophore produced an increased release of both saturated and unsaturated fatty acids and a concomitant increased formation of TxA2 and other arachidonate products. TxA2 (and possibly other cyclo oxygenase products) appears to have a significant role in ionophore-induced aggregation only when low concentrations (<1 μM) of the ionophore are employed.Testosterone added to rat or human platelet-rich plasma (PRP) was shown previously to potentiate platelet aggregation induced by ADP, adrenaline, collagen and arachidonic acid (1, 2). We show that testosterone also potentiates ionophore induced aggregation in washed platelets and in PRP. This potentiation was dose and time dependent and resulted from increased lipolysis and concomitant generation of TxA2 and other prostaglandin products. The testosterone potentiating effect was abolished by preincubation of the platelets with indomethacin.

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