scholarly journals Synergistic inhibition of platelet activation by plasmin and prostaglandin I2

Blood ◽  
1987 ◽  
Vol 69 (5) ◽  
pp. 1504-1507
Author(s):  
AI Schafer ◽  
GB Zavoico ◽  
J Loscalzo ◽  
AK Maas
Keyword(s):  
Cyclic Amp ◽  
Platelet Activation ◽  
Platelet Rich Plasma ◽  
Thromboxane A2 ◽  
Prostaglandin I2 ◽  
Synergistic Inhibition ◽  
Tissue Plasminogen ◽  
A Site ◽  
Induced Aggregation ◽  
Inhibition Of Thrombin

Endothelial cell prostacyclin (PGI2) inhibits platelet activation by raising platelet cyclic AMP. Previously, platelet activation was also shown to be blocked by plasmin formed by endothelium-derived tissue plasminogen activator (TPA). We have now studied interactions between PGI2 and plasmin in the control of platelet function. PGI2 and plasmin cause synergistic inhibition of thrombin- and ADP-induced aggregation of washed platelets. Inhibition by PGI2 is similarly potentiated by TPA added to platelet-rich plasma to generate plasmin. Thrombin-stimulated rise in platelet cytosolic Ca2+, measured by fura2 fluorescence, and thromboxane A2 formation, measured by radioimmunoassay (RIA), are likewise synergistically inhibited by PGI2 and plasmin. Plasmin neither increases nor potentiates PGI2-stimulated increases in platelet cyclic AMP. Thus, PGI2 and plasmin cause synergistic inhibition of platelet activation by both cyclic AMP-dependent and independent mechanisms. This interaction between two different endothelium-derived products may play an important role in localizing the hemostatic plug to a site of vascular injury by preventing further thrombin-mediated accrual of platelets.

scholarly journals Synergistic inhibition of platelet activation by plasmin and prostaglandin I2

Blood ◽  
1987 ◽  
Vol 69 (5) ◽  
pp. 1504-1507 ◽  
Author(s):  
AI Schafer ◽  
GB Zavoico ◽  
J Loscalzo ◽  
AK Maas
Keyword(s):  
Cyclic Amp ◽  
Platelet Activation ◽  
Platelet Rich Plasma ◽  
Thromboxane A2 ◽  
Prostaglandin I2 ◽  
Synergistic Inhibition ◽  
Tissue Plasminogen ◽  
A Site ◽  
Induced Aggregation ◽  
Inhibition Of Thrombin

Abstract Endothelial cell prostacyclin (PGI2) inhibits platelet activation by raising platelet cyclic AMP. Previously, platelet activation was also shown to be blocked by plasmin formed by endothelium-derived tissue plasminogen activator (TPA). We have now studied interactions between PGI2 and plasmin in the control of platelet function. PGI2 and plasmin cause synergistic inhibition of thrombin- and ADP-induced aggregation of washed platelets. Inhibition by PGI2 is similarly potentiated by TPA added to platelet-rich plasma to generate plasmin. Thrombin-stimulated rise in platelet cytosolic Ca2+, measured by fura2 fluorescence, and thromboxane A2 formation, measured by radioimmunoassay (RIA), are likewise synergistically inhibited by PGI2 and plasmin. Plasmin neither increases nor potentiates PGI2-stimulated increases in platelet cyclic AMP. Thus, PGI2 and plasmin cause synergistic inhibition of platelet activation by both cyclic AMP-dependent and independent mechanisms. This interaction between two different endothelium-derived products may play an important role in localizing the hemostatic plug to a site of vascular injury by preventing further thrombin-mediated accrual of platelets.

Different Effects of Aspirin, Dipyridamole and UD-CG 115 on Platelet Activation in a Model of Vascular Injury: Studies with Extracellular Matrix Covered with Endothelial Cells

1986 ◽  
Vol 56 (03) ◽  
pp. 333-339 ◽  
Author(s):  
A Eldor ◽  
I Vlodavsky ◽  
Z Fuks ◽  
T H Muller ◽  
W G Eisert
Keyword(s):  
Extracellular Matrix ◽  
Endothelial Cells ◽  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Platelet Activation ◽  
Platelet Rich Plasma ◽  
Thromboxane A2 ◽  
Phase Microscopy ◽  
Large Platelet ◽  
Platelet Aggregates

SummaryCultured endothelial cells produce an extracellular matrix (ECM) which activates platelets, similarly to deendothelialized vascular segments. Platelet-rich plasma (PRP) was incubated with endothelial cells cultures seeded in various densities on ECM. The interaction of the platelets with this artifical intima was evaluated by phase microscopy and by thromboxane A2 (TXA2) and prostacyclin (PGI2) measurement. Large platelet aggregates were formed on exposed ECM. Platelets aggregation but not adhesion on the ECM was markedly inhibited by the presence of endothelial cells. Pretreatment of the endothelial cells with 0.1 mM aspirin reduced their PGI2 synthesis and was associated with platelet aggregation on the ECM. 10 μM dipyridamole markedly inhibited platelet activation by ECM when the drug was added to citrated whole blood before PRP preparation. UD-CG 115 which elevates cyclic AMP in cardiac muscle, inhibited platelet aggregation and TXA2 production induced by ECM, in the presence as well as in the absence of endothelial cells, without any effect on endothelial PGI2 production.

Aspirin-Dependent Effects on Purinergic P2Y1 Receptor Expression

2019 ◽  
Vol 119 (05) ◽  
pp. 726-734 ◽  
Author(s):  
Isabella Massimi ◽  
Laura Alemanno ◽  
Maria Guarino ◽  
Raffaella Guerriero ◽  
Massimo Mancone ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Thromboxane A2 ◽  
Adenosine Diphosphate ◽  
Receptor Expression ◽  
P2y1 Receptor ◽  
Biochemical Pathway ◽  
Thromboxane A2 Receptor ◽  
Induced Aggregation

AbstractChronic treatment with aspirin in healthy volunteers (HVs) is associated with recovery of adenosine diphosphate (ADP)-induced platelet activation. The purinergic P2Y1 receptor exerts its effects via a Gq-protein, which is the same biochemical pathway activated by thromboxane-A2 receptor. We hypothesized that recovery of ADP-induced platelet activation could be attributed to increased P2Y1 expression induced by chronic aspirin exposure. We performed a multi-phase investigation which embraced both in vitro and in vivo experiments conducted in (1) human megakaryoblastic DAMI cells, (2) human megakaryocytic progenitor cell cultures, (3) platelets obtained from HVs treated with aspirin and (4) platelets obtained from aspirin-treated patients. DAMI cells treated with aspirin or WY14643 (PPARα agonist) had a significant up-regulation of P2Y1 mRNA, which was shown to be a PPARα-dependent process. In human megakaryocytic progenitors, in the presence of aspirin or WY14643, P2Y1 mRNA expression was higher than in mock culture. P2Y1 expression increased in platelets obtained from HVs treated with aspirin for 8 weeks. Platelets obtained from patients who were on aspirin for more than 2 months had increased P2Y1 expression and ADP-induced aggregation compared with patients on aspirin treatment for less than a month. Overall, our results suggest that aspirin induces genomic changes in megakaryocytes leading to P2Y1 up-regulation and that PPARα is the nuclear receptor involved in this regulation. Since P2Y1 is coupled to the same Gq-protein of thromboxane-A2 receptor, platelet adaptation in response to pharmacological inhibition seems not to be receptor specific, but may involve other receptors with the same biochemical pathway.

scholarly journals Impaired platelet response to thromboxane-A2 and defective calcium mobilization in a patient with a bleeding disorder

Blood ◽  
1981 ◽  
Vol 57 (3) ◽  
pp. 545-552 ◽  
Author(s):  
B Lages ◽  
C Malmsten ◽  
HJ Weiss ◽  
B Samuelsson
Keyword(s):  
Platelet Rich Plasma ◽  
Calcium Ionophore ◽  
Thromboxane A2 ◽  
Adenosine Diphosphate ◽  
Bleeding Disorder ◽  
Ionophore A23187 ◽  
Platelet Response ◽  
Thromboxane Synthetase ◽  
Defect Aggregation ◽  
Induced Aggregation

Abstract Platelet aggregation, secretion, and thromboxane formation induced by various agonists, including arachidonate, prostaglandin-G2 (PGG2), and thromboxane-A2 (TxA2), were examined in a patient with a bleeding disorder who was previously reported to have a TxA2-related defect. Aggregation and 14C-5HT secretion were decreased, and no TxB2 formation occurred in response to adenosine diphosphate (ADP), epinephrine, or collagen. Arachidonate-induced aggregation and TxB2 formation, and PGG2- induced aggregation (but not TxB2 formation) were impaired at low agonist concentrations. The patient's platelets did not aggregate in response to TxA2 generated from arachidonate in normal platelets, but were capable of synthesizing TxA2 from both arachidonate and PGG2. In addition, aggregation and secretion induced by low concentrations of the ionophore A23187 were impaired in platelet-rich plasma (PRP) and in gel-filtered platelets in the absence of extracellular calcium; these responses became normal at higher A23187 concentrations or, in GFP, at low A23187 concentrations in the presence of exogenous calcium. These findings indicate that the TxA2 defect in this patient does not result from a thromboxane synthetase deficiency, but may be due to impaired mobilization of platelet calcium, and thus are consistent with the possibility that TxA2 may act as a calcium ionophore.

Prostaglandins and Platelet Function in Diabetes

1979 ◽  
Author(s):  
J. García-Conde ◽  
J.A. Amado ◽  
J. Merino ◽  
I. Benet
Keyword(s):  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Normal Subjects ◽  
Inhibitory Effect ◽  
Rat Aorta ◽  
Diabetic Group ◽  
Diabetic Patients ◽  
Prostaglandin I2 ◽  
Induced Aggregation ◽  
Normal Controls

We have studied platelet aggregation induced by 0,5 mM. Araquidonic acid (AA) addition to platelet-rich-plasma (PRP) from 21 insulin treated diabetic patients and in 21 non-diabetic controls. The velocity of aggregation was significantly higher in the diabetic group. There was no differences in the velocity of aggregation in patients with or without retinopathy.The incubation of PRP of normal subjects at 37- during 5 minutes with 5,8 10-4 M. Imidazole changed the pattern of aggregation: The velocity of aggregation was slower and appeared a wave of disaggregation. Imida zole had not effect on aggregation in the diabetic group. This data add support to the findings published by COLWLLL showing that platelets from diabetics have hyperactive AA metabolism. Prostaglandin I2 (PGI2) obtained from rat aorta shows an inhibitory effect on ADP or AA induced aggregation. This effect is less marked in diabetic PRP than in PRP of normal controls. PGI2 release in platelet-poor-plasma from diabetics is normal. This can represent a resistance ot diabetic platelet to the anti aggregating effect of PGI 2. A similar finding was also appreciated with the PGE1 in three out of six patients so tar stu

scholarly journals Human group II 14 kDa phospholipase A2 activates human platelets

1997 ◽  
Vol 327 (1) ◽  
pp. 259-265 ◽  
Author(s):  
János POLGÁR ◽  
Ruth M. KRAMER ◽  
Suzane L. UM ◽  
Joseph A. JAKUBOWSKI ◽  
Kenneth J. CLEMETSON
Keyword(s):  
Phospholipase A2 ◽  
Platelet Activation ◽  
Heparan Sulphate ◽  
Thromboxane A2 ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Time Dependent ◽  
Human Group ◽  
Group Ii ◽  
Induced Aggregation

Recombinant human group II phospholipase A2 (sPLA2) added to human platelets in the low μg/ml range induced platelet activation, as demonstrated by measurement of platelet aggregation, thromboxane A2 generation and influx of intracellular free Ca2+ concentration and by detection of time-dependent tyrosine phosphorylation of platelet proteins. The presence of Ca2+ at low millimolar concentrations is a prerequisite for the activation of platelets by sPLA2. Mg2+ cannot replace Ca2+. Mg2+, given in addition to the necessary Ca2+, inhibits sPLA2-induced platelet activation. Pre-exposure to sPLA2 completely blocked the aggregating effect of a second dose of sPLA2. Albumin or indomethacin inhibited sPLA2-induced aggregation, similarly to the inhibition of arachidonic acid-induced aggregation. Platelets pre-treated with heparitinase or phosphatidylinositol-specific phospholipase C lost their ability to aggregate in response to sPLA2, although they still responded to other agonists. This suggests that a glycophosphatidylinositol-anchored platelet-membrane heparan sulphate proteoglycan is the binding site for sPLA2 on platelets. Previous reports have stated that sPLA2 is unable to activate platelets. The inhibitory effect of albumin and Mg2+, frequently used in aggregation studies, and the fact that isolated platelets lose their responsiveness to sPLA2 relatively quickly, may explain why the platelet-activating effects of sPLA2 have not been reported earlier.

Aspirin Ingestion in Primary Thrombocythemia

1982 ◽  
Vol 48 (01) ◽  
pp. 072-075 ◽  
Author(s):  
Akira Hattori ◽  
Masayoshi Sanada ◽  
Reizo Nagayama ◽  
Akira Shibata ◽  
Minoru Okuma
Keyword(s):  
Single Dose ◽  
Arterial Thrombosis ◽  
Platelet Rich Plasma ◽  
Thromboxane A2 ◽  
Primary Thrombocythemia ◽  
Normal Humans ◽  
Spontaneous Platelet Aggregation ◽  
Induced Aggregation ◽  
Aspirin Ingestion

SummaryRecently Massotti et al. (14) and Patrono et al. (23) have proposed for antithrombotic therapy the use of small single dose of aspirin (ASA) every three or four days in order to inhibit thromboxane A2 production in the platelets but not to inhibit PGI2 production in the endothelium. Their data are theoretical and based on a small number of normal humans. We have examined the effect of a single ingestion of ASA (10 mg/kg) on spontaneous platelet aggregation (SPA) and collagen-induced aggregation (CA) in 11 patients with primary thrombocythemia using the original platelet-rich plasma. SPA and CA were positive in 8 out of 10 and in 11 out of 11 patients respectively before ASA ingestion. ASA abolished both types of aggregation in all patients at 12 h after the ingestion. But the recovery occurred in 1/11 in CA at 24 hr, in about half (3/8 SPA or 7/11 CA) of the patients at 48 hr, in 5/8 (SPA) and 10/11 (CA) at 72 hr and in 7/ 8 (SPA) and 11/11 (CA) at 96 hr. Since SPA and sometimes CA have been considered to be the parameters of the effect of ASA on hyperreactivity of the platelets in vivo, resulting in arterial thrombosis or insufficiency in these patients, our results suggest that daily or at least once per two days ingestion of ASA may be necessary in these patients. These results were discussed in relation to the platelet survivals (6.5–10 days) and the platelet cyclo-oxygenase or lipoxygenase activities (deficient in 3 patients for the former and in 2 for the latter) in our patients.

scholarly journals Inhibition of agonist-induced platelet aggregation, Ca2+ mobilization and granule secretion by guanosine 5′-[β-thio]diphosphate and GDP in intact platelets. Evidence for an inhibitory mechanism unrelated to the inhibition of G-protein-GTP interaction

1988 ◽  
Vol 250 (1) ◽  
pp. 209-214 ◽  
Author(s):  
S Krishnamurthi ◽  
Y Patel ◽  
V V Kakkar
Keyword(s):  
Platelet Aggregation ◽  
G Protein ◽  
Platelet Activation ◽  
Human Platelet ◽  
Inhibitory Mechanism ◽  
Inhibitory Effects ◽  
Similar Concentration ◽  
Granule Secretion ◽  
Induced Aggregation ◽  
Inhibition Of Thrombin

The effect of guanosine 5′-[beta−thio]diphosphate (GDP[beta S]), reported to be an antagonist of GTP at the G-protein-binding site, on human platelet activation was examined. GDP[beta S] (0.3-3 mM) had significant inhibitory effects on platelet aggregation and 5-hydroxytryptamine (5HT) secretion induced by thrombin, collagen, the thromboxane mimetic U46619 and 1,2-dioctanoylglycerol (diC8) in intact platelets, as well as in saponin-permeabilized platelets. Similar inhibitory effects in intact platelets were also observed with ATP (over similar concentration ranges) and GDP and GTP (at 2- and 10-fold higher concentrations respectively). All four nucleotides also inhibited ADP-induced platelet aggregation in indomethacin-treated platelets under conditions where no 5HT secretion occurred. Inhibition of thrombin-induced aggregation and secretion by GDP[beta S] and ATP in intact platelets was accompanied by a reduction in the thrombin-induced rise in intracellular Ca2+ levels and 45 kDa-protein phosphorylation. The results suggest that at least some of the effects of GDP[beta S] may be unrelated to inhibition of G-protein-GTP interaction, but, instead, may be mediated via an extracellular site, common to all the nucleotides tested and perhaps via inhibition of the effects of endogenous/released ADP. The usefulness of GDP[beta S] as a tool in studying G-protein-GTP interactions in platelets is thus questionable.

scholarly journals The Effect of Tirofiban on Fibrinogen/Agonist-Induced Platelet Shape Change and Aggregation

2008 ◽  
Vol 14 (3) ◽  
pp. 295-302 ◽  
Author(s):  
I. Anita Jagroop ◽  
Dimitri P. Mikhailidis
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Whole Blood ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Adenosine Diphosphate ◽  
Vascular Events ◽  
Spontaneous Platelet Aggregation ◽  
Induced Aggregation ◽  
Platelet Shape

There is evidence linking raised plasma fibrinogen (fib) and platelet hyperactivity with vascular events. One way to inhibit platelets is to block the platelet membrane glycoprotein (GP) IIb/IIIa receptor, which binds circulating fib or von Willebrand factor and cross-links platelets at the final common pathway to platelet aggregation. Tirofiban is a potent and specific fib receptor antagonist, used in the treatment of unstable angina. The authors assessed the effect of tirofiban on spontaneous platelet aggregation (SPA), fib-induced, serotonin (5HT)-induced, and adenosine diphosphate (ADP)-induced aggregation in whole blood by calculating the percentage free platelet count. These various agonists were used alone and in combination. The authors also measured the effect of tirofiban on agonists-induced (ADP, 5HT) platelet shape change (PSC). The effect of fib on PSC was also evaluated in platelet-rich plasma using a high-resolution (0.07 fL) channelyzer. Tirofiban significantly inhibited SPA, fib (2, 4, 8 g/L), ADP, ADP + fib combination, and 5HT-induced aggregation. Tirofiban had no effect on agonist-induced PSC. There was no apparent change in platelet volume with fib. In conclusion, tirofiban does not appear to have an effect on PSC, an early phase of platelet activation. Tirofiban seems to be a nonspecific and an effective inhibitor of platelet aggregation (a later phase of platelet activation) in whole blood. The clinical significance of these findings remains to be established.

SELECTIVE ANTAGONISTS OF PAF: INTERFERENCE WITH PLATELET FUNCTION AND EFFECT ON THROMBOGENESIS INDUCED BY SUBENDOTHELIUM.

1987 ◽  
Author(s):  
P Hadvary ◽  
H R Baumgartner
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Ex Vivo ◽  
Platelet Rich Plasma ◽  
Thrombus Formation ◽  
Blood Platelets ◽  
Rabbit Aorta ◽  
Constant Infusion ◽  
Induced Aggregation

Platelet activating factor (PAF) is a very potent excitatory agonist of blood platelets but the physiological importance of this mediator in platelet thrombus formation is not known. We investigated the effect of two chemically unrelated selective inhibitors of PAF-induced platelet aggregation on thrombogenesis induced by rabbit aorta subendothelium (SE) using an ex vivo perfusion system.Ro 19-3704 is a highly potent inhibitor structurally related to PAF. This compound inhibits PAF-induced aggregation of rabbit platelets in platelet rich plasma in vitro competitively. Against 4 nM PAF, a concentration resulting in submaximal platelet aggre-gregation velocity, the IC50 was 70 nM. Inhibition was highly selective for PAF-induced aggregation, since aggregation induced by collagen (HORM, 5 yg/ml), ADP (1 yM) or thrombin (0.4 U/ml) was not inhibited even at a concentration as high as 10 yM. Bro-tizolam, a triazolobenzodiazepine reported to be a selective inhibitor of PAF-induced platelet activation, had in our system an IC50 of 200 nM. The selective benzodiazepine antagonist Ro 151788 was without effect on inhibition of PAF-induced platelet activation by brotizolam.Ro 19-3704 was given intravenously to rabbits as a bolus of 0.2 mg/kg followed by constant infusion of 0.02 mg/kg/min. This dosage provoked ex vivo a constant right shift ratio of the dose response curve for PAF-induced aggregation (RSR[PAF]) by a factor of 25 to 35. Brotizolam was given orally at a dose of 100 mg/ kg together with 300 mg/kg of Ro 15-1788 (to antagonize the central effects) 90 minutes before starting the perfusion experiment, resulting in a RSR[PAF] of 35 to 135. ADP induced platelet aggregation was not impaired by either compound. SE was exposed to the non-anticoagulated blood withdrawn from the carotid artery for 3 min at 2600 s-1 and for 20 min at 200 s-1 shear rate. Quantitative morphometric evaluation showed that SE coverage by platelets and by fibrin, thrombus area and thrombus height were all unchanged by the PAF antagonists at low and at high shear rates despite a very substantial inhibition of PAF-induced platelet aggregation. Therefore a major role of PAF in SE-induced thrombogenesis seems unlikely.

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