Adenosine 5’-O-(2-Thiodiphosphate) (ADP-β-S) Is A Partial Agonist At The ADP Receptor Of Human Platelets

1981 ◽  
Author(s):  
N J Cusack ◽  
S M O Hourani
Keyword(s):  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Human Platelet ◽  
Partial Agonist ◽  
Human Platelets ◽  
Simultaneous Addition ◽  
Prostaglandin Receptor ◽  
Human Platelet Aggregation ◽  
Adp Receptor ◽  
Stimulation Of

ADP induces human platelet aggregation and inhibits the stimulation of platelet adenylate cyclase by prostaglandin E1 (PGE1), but analogues of ADP in which the diphosphate group is modified retain only weak aggregating activity. However, ADP-β-S, an ADP analogue in which a terminal phosphate oxygen is replaced by sulphur, is known to be equipotent with ADP as an inhibitor of PGE1-stimulated adenylate cyclase in purified human platelet membranes. We therefore tested ADP-β-S on intact human platelets. ADP-β-S induced human platelet aggregation and inhibited PGE1-stimulated adenylate cyclase, but in botn cases was less potent than ADP and only achieved 75% and 50% respectively of the maximal effects of ADP. Aggregation induced by ADP-β-S was competitively inhibited by ATP (50 μM), a known ADP antagonist.Both these actions of ADP could be inhibited by the simultaneous addition of ADP-β-S (50 μM). Aggregation induced by a stable endoperoxide analogue (11 ,9 -epoxymethano PGH2), which acts at a prostaglandin receptor rather than at an ADP receptor, was not inhibited by the simultaneous addition of ADP-β-S (50 μM). The behaviour of ADP-β-S towards human platelets is therefore tnat of a partial agonist at the ADP receptor.

5'-N-Ethylcarboxamidoadenosine (NECA) Is A Potent, Stereospecific Inhibitor Of Human Platelet Aggregation

1981 ◽  
Author(s):  
N J Cusack ◽  
S M O Hourani
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Human Platelet ◽  
Human Platelets ◽  
Inhibit Platelet Aggregation ◽  
Inhibitory Potency ◽  
Adenosine Receptor Antagonist ◽  
Human Platelet Aggregation ◽  
Potent Vasodilator

Adenosine is a vasodilator, and also inhibits platelet aggregation apparently by acting at an external membrane receptor to increase levels of platelet cyclic AMP. Certain analogues of adenosine retain activity as vasodilators, and also inhibit platelet aggregation by raising levels of platelet cyclic AMP. NECA is an extraordinarily potent vasodilator, so its effects on human platelet function were tested.NECA (1 μM) inhibited human platelet aggregation induced by ADP, 5-HT, thrombin and adrenaline mere powerfully than adenosine (1 μM). NECA, even at micrcmolar concentrations, was 5 to 10 times more potent than adenosine as an inhibitor of aggregation induced by ADP (5μM or 200μM) or adrenaline (200μM). NECA (Ka = 0.95μM) caused increases in levels of platelet cyclic AMP, which could be competitively inhibited by theophylline (Ki = 8μM), an adenosine receptor antagonist. However, here NECA was only about 1.3 times more potent than adenosine (Ka = 1.2μM). The effects of NECA, like those of adenosine, were completely stereospecific, the L enantiomer of NECA being inactive. NECA (10μM) did not prevent inhibition of PGE1-stimulated adenylate cyclase by ADP (5 μM).NECA is the most potent analogue of adenosine yet tested on human platelets, and is the first example of a 5' modification to retain significant inhibitory potency.

Differential Ability of Agonists to Express Distinct Pools of Fibrinogen (Gpllb/llla) Receptors which Can Mediate the Aggregation of Human Platelets

1989 ◽  
Vol 62 (03) ◽  
pp. 955-961 ◽  
Author(s):  
Ian S Watts ◽  
Rebecca J Keery ◽  
Philip Lumley
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Surface Membrane ◽  
Blood Platelet ◽  
Human Platelets ◽  
Membrane Glycoprotein ◽  
Platelet Surface ◽  
Human Platelet Aggregation ◽  
Differential Ability ◽  
Blood Platelet Aggregation

SummaryWe have investigated the effect of two procedures that modify human platelet surface membrane glycoprotein (Gp) IIb and IIIa complexes upon whole blood platelet aggregation to a range of agonists. (A) Irreversible disruption of complexes by temporary (30 min) Ca2+-deprivation with EGTA at 37° C. (B) Binding of a monoclonal antibody M148 to the complex. EGTA exposure abolished aggregation to ADP, adrenaline and PAF. In contrast, full aggregation curves to collagen and U-46619 could still be established. EGTA exposure reduced M148 binding to platelets by 80%. Excess M148 abolished aggregation to ADP, PAF, collagen and U-46619. However, upon removal of unbound antibody from platelets full aggregation curves to collagen and U-46619 but not to ADP and PAF could be re-established. Thus human platelet aggregation to ADP, PAF and adrenaline appears absolutely dependent upon surface membrane GpIIb/IIIa complexes. In contrast, collagen and U-46619 cause expression of an additional distinct pool of Gp complexes inaccessible to EGTA and M148 in unstimulated platelets which is intimately involved in aggregation to these agonists.

Nanoparticles That Display Short Collagen-Related Peptides. Potent Stimulation of Human Platelet Aggregation by Triple Helical Motifs

2007 ◽  
Vol 18 (4) ◽  
pp. 1025-1027 ◽  
Author(s):  
Mabel A. Cejas ◽  
Cailin Chen ◽  
William A. Kinney ◽  
Bruce E. Maryanoff
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Human Platelet Aggregation ◽  
Stimulation Of

Potentiation of Adrenaline-Induced Platelet Aggregation by Angiotensin II

1985 ◽  
Vol 54 (03) ◽  
pp. 717-720 ◽  
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

Evidence for Two Separate Receptors Mediating The Stimulation of Platelet Adenylate Cyclase By Prostaglandin I2 (PGI2), PGD2 and PGE1

1979 ◽  
Author(s):  
D. C. B. Mils ◽  
D. E. Macfarlane
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Partial Agonist ◽  
Human Platelets ◽  
Intrinsic Activity ◽  
High Dose ◽  
Prostaglandin I2 ◽  
Subsequent Response ◽  
High Concentrations ◽  
Stimulation Of

Prostacyclin (PGI2), and prostaglandins D2 and E1, all inhibit aggregation of human platelets by stimulating adenylate cyclase. in platelets prelabelled with l4C adenine, PGI2 has a higher intrinsic activity than either PGD2 or PGE1, as well as a higher apparent affinity. PGE1 but not PGD2, inhibits the action of high concentrations of PGI2, both when added simultaneously with PGI2 and when added 3 min later. in the latter case the slow spontaneous fall in intracellular cyclic AMP is accelerated by PGE. but not by PGD2. PGF1α, at concentrations up to 100 μM neither stimulated the cyclase 1 by itself, nor did it inhibit the effects of PGI2, PGE1, or PGD2. PGF2α, which did cause a small increase in cyclic AMP, inhibited PGD2 strongly, PGE1 not at all, and PGI2 slightly at high concentrations. N0164, an inhibitor of aggregation induced by bis-enoic prostaglandins, inhibited cyclase stimulation by PGD2 but not by PGE1, PGE2, PGD1 or PGI2, though it reduced PGI2-induced inhibition of platelet aggregation. Preaddition of PGE1, but not of PGI2 or PGD2, at submaximal concentrations, inhibited subsequent response to high dose PGI2. The results suggest that PGE1 and PGD2 probably act on the same enzyme, but through a different receptor. PGE1 acts as a partial agonist for the receptor for PGI2, but in addition causes a tachyphylaxis not seen with PGI2 or with PGD2.

Prostaglandins (PG) Inhibit Human Platelet Aggregation by PG Receptor Antagonism as well as Adenylate Cyclase Stimulation

1979 ◽  
Author(s):  
D.E. MacIntyre ◽  
E.W. Salzman
Keyword(s):  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Human Platelet ◽  
High Ratio ◽  
Receptor Antagonism ◽  
Human Platelet Aggregation ◽  
Alkyl Groups ◽  
Low Concentrations ◽  
Alkyl Substitution ◽  
Adenylate Cyclase Stimulation

11-Deoxy and/or 15 or 16 alkyl substitution confer platelet aggregating activity to bis-enoic PG's: e.g., 11-deoxy-PGE2 (threshold (T)-5μM); ll-deoxy-15(S)-15-methyl-PGE2 (T=0.1μM);ll-deoxy-15(S)-16-methyl-PGE2(T=0.1μM). Responses induced by such PG’s mimic those induced by PGH2 and PGH2 analogues (e.g., U44069). N0164 competitively inhibits aggregation induced by PG’s and suppresses “secondary” responses induced by low concentrations of ADP or arachidonic acid, suggesting involvement of a specific PG stimulatory receptor in platelet aggregation. We compared non-aggregatory PG’s as inhibitors of pri mary aggregation induced by ADP or U44069. PG’s containing 11-deoxy and/or 16-alkyl groups selectively inhibited aggregation induced by U44069. Mean I50 values (n-4) against ADP and U44069 respectively were PGA2 (>100μM; 0.3μM); PGB2 (>100μM; 5μM); PGD2 (6nM; 2nM); PGE1(10nM; 5nM); 11-deoxy PGE1 (60μM; 2μM); ll-deoxy-15-(R)-16-methyl (100μM; 2μM); 13,14-dihydro-16-methyl-PGE2 methyl ester(750nM; 15nM). A low ADP: 406 I50 ratio (e.g., PGD2) indicates that inhibition is mainly due to adenylate cyclase stim ulation, and a high ratio (e.g., PGA2) that inhibition is mainly due to PG receptor antagonism. We have demonstrated a PG stimulatory receptor on the platelet, and its involvement in “secondary” aggregation. PG’s inhibit aggregation by combining with this receptor and/or by stimulating adenylate cyclase.

scholarly journals Human platelet aggregation by murine monoclonal antiplatelet antibodies is subtype-dependent

Blood ◽  
1993 ◽  
Vol 81 (7) ◽  
pp. 1792-1800 ◽  
Author(s):  
S De Reys ◽  
C Blom ◽  
B Lepoudre ◽  
PJ Declerck ◽  
M De Ley ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Platelet Aggregation ◽  
Platelet Activation ◽  
Human Platelet ◽  
Human Platelets ◽  
Antigen Recognition ◽  
Metabolic Inhibitors ◽  
Antigen Binding ◽  
Human Platelet Aggregation ◽  
Murine Monoclonal Antibodies

Abstract Twenty murine monoclonal antibodies (MoAbs) generated against different human platelet antigens induced clumping of human platelets in plasma and buffer. Whereas one MoAb could agglutinate platelets, clumping for 19 MoAbs was blocked by metabolic inhibitors, indicating that these induce platelet activation. Fifteen MoAbs were of IgG1, two of IgG2a, and two of IgG2b subtype. F(ab')2 fragments of these did not evoke an aggregatory response, but specifically inhibited aggregations by and binding of their respective intact MoAbs to platelets. Single-platelet counting technology indicated that the MoAbs bind through their antigen- binding and Fc domains mainly to the surface of the same platelet, rather than cause interplatelet-binding. Despite these similarities, the mechanism of action was nevertheless subtype-dependent. Aggregation induced by all IgG1 antibodies could consistently be prevented by blocking the Fc gamma II-receptor, whereas aggregations induced by all IgG2 antibodies still occurred with blocked Fc-receptor, provided functional complement was present. We therefore conclude that platelet activation by MoAb-binding is initiated by antigen recognition followed by an Fc domain-dependent step, which involves the Fc gamma II-receptor for IgG1-type MoAbs and complement-binding for IgG2-type MoAbs. Thus, antibodies of different subtypes can aggregate platelets via different pathways.

Thromboxane A2-Stimulated Human Platelet Aggregation Is Potentiated By Epinephrine Acting VIA Alpha Adrenergic Receptors

1981 ◽  
Author(s):  
G J Johnson ◽  
G H R Rao ◽  
J G White
Keyword(s):  
Platelet Aggregation ◽  
Adrenergic Receptors ◽  
Human Platelet ◽  
Thromboxane A2 ◽  
Human Platelets ◽  
Adrenergic Agents ◽  
Alpha Adrenergic Receptors ◽  
Human Platelet Aggregation ◽  
Induced Aggregation

Epinephrine (E) potentiates arachidonate (A)-induced aggregation of human platelets. A-insensitive dog platelets (AIP), that form thromboxane A2 (T) but do not aggregate when stirred with A alone, aggregate when exposed to E + A. Therefore, we studied the effect of E on T-stimu- lated human platelet aggregation. AIP stirred with A formed T which was confirmed by TLC. 1/100 to 1/200 volume of AIP was removed 30 sec. after A, and transferred to gel- filtered, aspirin-incubated human platelets. Recipient platelet aggregation was proportional to the volume of AIP transferred. The addition of the thromboxane synthetase inhibitor, Azo Analog I, abolished the aggregating activity of AIP. Transfer of an aliquot of AIP that was inadequate to aggregate human gel-filtered, aspirin-incubated platelets resulted in irreversible aggregation in the presence of ≥0.5nM E. E potentiated aggregation when added 3 min. before but not 3 min. after aliquot transfer. T-stimulated aggregation was abolished by the T-antagonist, 13 azapro- stenoic acid (APA), but E added after APA and before T restored aggregation. E potentiation of T-stimulated aggregation was abolished by prior exposure to equimolar yohimbine, dihydroergocryptine and phentolamine, agents that bind to alpha2 adrenergic receptors, but not by prazosin an alpha1 antagonist. Higher concentrations of E reversed the inhibitory effects of the alpha2 adrenergic agents. All of these agents in higher concentrations (1-100μM) also blocked aggregation induced by T alone. Therefore T-induced platelet aggregation is potentiated by E, in concentrations attained in vivo, by a mechanism linked to platelet alpha adrenergic receptors. Platelet alpha2 receptors have a close functional relationship to the postulated T receptor. E may initiate platelet aggregation in vivo when T is formed in quantities inadequate to alone induce aggregation.

Sign in / Sign up

Export Citation Format

Share Document