Pharmacology Of 12-Deoxyphorbol Phenyl Acetate (12-DOPP) Induced Human Platelet Aggregation

1981 ◽  
Author(s):  
J Westwick ◽  
E M Williamson ◽  
F J Evans ◽  
V V Kakkor
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Divalent Cations ◽  
Dienoic Acid ◽  
Free Radical Scavengers ◽  
Phenyl Acetate ◽  
Lipoxygenase Inhibitor ◽  
Human Platelet Aggregation ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

12-DOPP (0.1 to 3.6µM) induced human platelet aggregation which was dependent upon the presence of divalent cations, intracellular level of C-AMP and an intact microtubular system in common with other aggregating agents. However, the small amount of platelet secretion and thromboxane (Tx) B2 synthesis did not contribute to 12-DOPP induced platelet aggregation as neither the Tx/endoperoxide antagonists pinane A2 (0.001-0.004mM) and trimethoquinone (0.01-0.1mM), the Tx synthesis inhibitors clotrimazole (0.1 to 0.8mM) and 9, 11, aza-prosta-5-13 dienoic acid (0.002-0.1) nor the cyclo-oxygenase inhibitor indomethacin (0.03-0.1mM) inhibited 12-DOPP induced aggregation. Furthermore the free radical scavengers aminopyrine (0.2-2.0mM), thioanisole (0.2-2.0mM) and butylated hydroxy toluene (0.07-1.4mM); the lipoxygenase inhibitor phenidone (0.5mM) and the leucotriene B and C antagonist FPL55712 (0.005-0.06mM) failed to modify 12-DOPP induced aggregation.However compounds which are thought to act as phospholipase inhibitors bromophenacyl bromide (0.3mM), mepracrine (0.20mM) and propanolol (0.2mM) were found to be effective inhibitors of 12-DOPP induced aggregation as well as the so- called calmodulin antagonists imipramine (0.12mM), desmethy- 1imipramine (0.033mM), promethazine (0.1mM) and trifluoperazine (0.35mM).The aggregation induced by 12-DOPP involves a direct effect upon platelets followed by the release of unknown substances probably phospholipids, which induce further aggregation of platelets.

Dependence of Human Platelet Functional Responses on Divalent Cations: Aggregation and Secretion in Heparin- and Hirudin-Anticoagulated Platelet-Rich Plasma and the Effects of Chelating Agents

1981 ◽  
Vol 45 (02) ◽  
pp. 173-179 ◽  
Author(s):  
Bruce Lages ◽  
Harvey J Weiss
Keyword(s):  
Platelet Aggregation ◽  
Chelating Agents ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Divalent Cations ◽  
Normal Subjects ◽  
Concentration Addition ◽  
Functional Responses ◽  
Induced Aggregation

SummaryThe dependence of ADP- and epinephrine-induced platelet aggregation and secretion on extracellular divalent cations was examined by quantitating these responses in citrate-, heparin-, and hirudin-anticoagulated platelet-rich plasma. ADP-induced 14C-5HT secretion in heparin-PRP and hirudin-PRP was generally decreased, relative to that in citrate-PRP, without corresponding reductions in aggregation, whereas in response to epinephrine, both aggregation and secretion were decreased in heparin-PRP, and abolished in hirudin-PRP. In heparin-PRP, but not in hirudin-PRP, the degree to which these responses were altered was highly variable among normal subjects, and was dependent on the anticoagulant concentration. Addition of citrate restored the extent of ADP-induced secretion and of epinephrine-induced aggregation and secretion in heparin-PRP to that observed in citrate-PRP, and increased the extent of ADP-induced secretion in hirudin-PRP. Addition of EDTA or EGTA, however, had no effect on ADP-induced secretion in heparin-PRP. These results suggest that ADP-induced aggregation and secretion, as well as responses to ADP vs. epinephrine, have different dependencies on extracellular or surface-bound divalent cations. The variable responses observed in heparin-PRP may reflect direct interactions of heparin with platelets, and this variability may account for the conflicting results of previous studies.

Requirement Of Fibrinogen And Calcium For Inter-Platelet Bridges In Platelet Aggregation: A Hypothesis

1981 ◽  
Author(s):  
Elizabeth Kornecki ◽  
Stefan Niewiarowski
Keyword(s):  
Platelet Aggregation ◽  
Binding Sites ◽  
Proteolytic Enzymes ◽  
Divalent Cations ◽  
Platelet Surface ◽  
Fibrinogen Binding ◽  
Platelet Aggregates ◽  
High Concentrations ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

Fibrinogen and calcium are required for the aggregation of platelets stimulated by ADP or pre-treated with proteolytic enzymes. Specific platelet surface fibrinogen binding sites (receptors) are exposed after platelets are stimulated by ADP or pre-treated with Chymotrypsin or pronase. It has previously been shown in our laboratory that an intact, symmetrical fibrinogen molecule is essential for fibrinogen binding and fibrinogen-induced aggregation of both ADP-stimulated and proteolytically-treated platelets. Here we propose that the mechanism by which fibrinogen and calcium aggregate platelets is by forming inter-platelet bridges linking the fibrinogen receptors of adjacent platelets together. In support of this proposition are the following new lines of evidence: 1) The fibrinogen-induced aggregations of ADP-stfiliulated or proteolytically-treated platelets are inhibited by high concentrations of fibrinogen (Ki=2.6 and 8.5 × 10 5M, respectively). The fibrinogen binding sites on adjacent platelets, at these concentrations, would be saturated by fibrinogen and therefore no inter-platelet fibrinogen bridges could be formed to hold the platelets together. 2) ADP-stimulated or chymotrypsin-treated platelets aggregated by fibrinogen are deaggregated by Chymotrypsin or pronase and this deaggregation coincides with the loss of 125I-fibrinogen from the platelet surface. 3) Preincubation of platelets with EDTA results in inhibition of both platelet aggregation and 125I-fibrinogen binding. Following the aggregations of ADP-stimulated or of chymotrypsin-treated platelets by fibrinogen, the addition of EDTA to the platelet aggregates results in both their deaggregation and their loss of bound 125I-fibrinogen. Thus it appears that divalent cations, especially calcium, are essential for the formation of fibrinogen-linked platelet aggregates.

Inhibition of Human and Rat Platelet Aggregation by Extracts of Mo-er (Auricularia auricula)

1982 ◽  
Vol 48 (02) ◽  
pp. 162-165 ◽  
Author(s):  
K C Agarwal ◽  
F X Russo ◽  
R E Parks
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Human Platelet ◽  
Rapid Onset ◽  
Hot Water ◽  
Inhibitory Effects ◽  
Inhibition Of Platelet Aggregation ◽  
Auricularia Auricula ◽  
Human Platelet Aggregation ◽  
Induced Aggregation

SummaryHot water extracts of Mo-er (1 gm by 15 ml of water), an oriental food (Auricularia auricula), inhibit strongly both human and rat platelet ADP-induced aggregation. HPLC analysis of two varieties of Mo-er, A.auricula and A.polytricha (a black tree fungus), shows that they contain adenosine (Ado), 133 and 154 micrograms per gram of dry fungus, respectively. The inhibition of ADP-induced platelet aggregation by Mo-er extracts and by Ado was compared. Mo-er extracts caused a more rapid onset and a longer duration of inhibition than produced by equivalent amounts of Ado. Furthermore, Mo-er extract treated with adenosine deaminase to degrade the Ado retained the capacity to inhibit platelet aggregation. The inhibitory effects of Mo-er extracts on ADP-induced human platelet aggregation are greatly potentiated by the inhibitors of cyclic AMP phosphodiesterase such as oxagrelate (phthalazinol) and papaverine. The inhibition of platelet aggregation is only partially blocked by 2’,5’-dideoxy-adenosine (DDA), an inhibitor of platelet adenylate cyclase and 5’-deoxy, 5’-methylthioadenosine (MTA), an antagonist of Ado receptors. ADP-induced rat platelet aggregation is strongly inhibited by Mo-er extracts, but not by Ado. This inhibition is not reversed by either DDA or MTA. These findings indicate that Mo-er extracts contain an agent (or agents) in addition to Ado, that blocks platelet aggregation by a mechanism that does not involve the platelet cyclic AMP system.

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.

The effects of an ASA-like hydroperoxide compound on adenosine diphosphate induced platelet aggregation

1984 ◽  
Vol 62 (3) ◽  
pp. 338-340
Author(s):  
J. J. F. Killackey ◽  
B. A. Killackey ◽  
I. Cerskus ◽  
R. B. Philp
Keyword(s):  
Platelet Aggregation ◽  
Acetylsalicylic Acid ◽  
Pharmacological Property ◽  
Human Platelet ◽  
Adenosine Diphosphate ◽  
Second Phase ◽  
Release Reaction ◽  
Human Platelet Aggregation ◽  
Second Phases ◽  
Induced Aggregation

A hydroperoxide compound structurally related to acetylsalicylic acid, 3-hydroperoxy-3-methylphthalide, inhibits both the first and second phases of adenosine diphosphate induced, biphasic, human platelet aggregation. This occurs over the same concentration range (0.05–0.5 mM) that acetylsalicylic acid inhibits second phase aggregation and the release reaction only. The complete inhibition of adenosine diphosphate induced aggregation is a unique pharmacological property for an acetylsalicylic-acid-like compound.

scholarly journals Low concentrations of lipid hydroperoxides prime human platelet aggregation specifically via cyclo-oxygenase activation

1997 ◽  
Vol 325 (2) ◽  
pp. 495-500 ◽  
Author(s):  
Catherine CALZADA ◽  
Evelyne VERICEL ◽  
Michel LAGARDE
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Lipid Peroxides ◽  
Human Platelets ◽  
Lipid Hydroperoxides ◽  
Cellular Functions ◽  
Human Platelet Aggregation ◽  
Low Concentrations ◽  
Oxygenase Activity ◽  
Aggregation Of Platelets

There is mounting evidence that lipid peroxides contribute to pathophysiological processes and can modulate cellular functions. The aim of the present study was to investigate the effects of lipid hydroperoxides on platelet aggregation and arachidonic acid (AA) metabolism. Human platelets, isolated from plasma, were incubated with subthreshold (i.e. non-aggregating) concentrations of AA in the absence or presence of hydroperoxyeicosatetraenoic acids (HPETEs). Although HPETEs alone had no effect on platelet function, HPETEs induced the aggregation of platelets co-incubated with non-aggregating concentrations of AA, HPETEs being more potent than non-eicosanoid peroxides. The priming effect of HPETEs on platelet aggregation was associated with an increased formation of cyclo-oxygenase metabolites, in particular thromboxane A2, and was abolished by aspirin, suggesting an activation of cyclo-oxygenase by HPETEs. It was not receptor-mediated because the 12-HPETE-induced enhancement of AA metabolism was sustained in the presence of SQ29,548 or RGDS, which blocked the aggregation. These results indicate that physiologically relevant concentrations of HPETEs potentiate platelet aggregation, which appears to be mediated via a stimulation of cyclo-oxygenase activity.

Effects “in Vitro” of Some Cardiovascular Drugs and Other Agents on Human Platelet Aggregation

1973 ◽  
Vol 29 (01) ◽  
pp. 190-195 ◽  
Author(s):  
G Sacchetti ◽  
D Bellani ◽  
C Montanari ◽  
A Gibelli
Keyword(s):  
Platelet Aggregation ◽  
Mechanism Of Action ◽  
Human Platelet ◽  
Cardiovascular Drugs ◽  
Blocking Drug ◽  
Human Platelet Aggregation ◽  
Vitro Effect ◽  
Induced Aggregation

SummaryThe in vitro effect of the following substances on human platelet aggregation is studied: K 4423 (a ß-blocking drug), isoproterenol, phentolamine, papaverine, methamidoline (a myolytic agent).None of these substances causes aggregation. All inhibit aggregation induced by ADP or noradrenaline, except for phentolamine, which is active only on noradrenaline- induced aggregation.Hypothesis on the mechanism of action of the compounds tested are proposed.

Human Platelet Aggregation Without Thromboxane (Tx) Formation

1981 ◽  
Author(s):  
J Westwick ◽  
J B Smith ◽  
V V Kakkar
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Human Platelets ◽  
Synthesis Inhibitor ◽  
Thromboxane Receptor ◽  
Human Platelet Aggregation ◽  
Thromboxane Receptor Antagonist ◽  
Induced Aggregation ◽  
Carbocyclic Thromboxane A2

It is not known whether PG endoperoxides have to be converted to TxA2 in order to induce aggregation and secretion We have examined this crucial question by measuring human platelet aggregation, 14C-5HT release and TxB2 formation induced by collagen, arachidonic acid (AA), adrenaline, U46619 and PGH2 in presence of either 1) 1-2-(4-carboxy-phenoxy) ethyl imidazole hydrochloride, a potent and selective thromboxane synthesis inhibitor (TSI) or a carbocyclic thromboxane A2 (CTA) - a so called thromboxane receptor antagonist. TSI, 1.5 to 75μM produced a dose related inhibition (IC50 5μM n=5) of Tx and elevation of PGE2 synthesis in adrenaline (8μM) and collagen (1.5μg/ml) stimulated platelets. When 14C-SHT labelled platelets were stimulated with 4.5μM adrenaline in the presence of 0, 2.5, 15 and 300μM TSI a 35±2.8, 27±0.5, 24.5±5.0% release of 14C-5HT release resulted and a 10014, 9612, 9711 and 9114% of control aggregation occurred. Similarly when human platelets were stimulated with 0.8mMAA a 51±1.4% (mean ±SE) release of 14C-5HT occurred, while in the presence of 15, 75 and 300μM of UK, a 42±0.4, 32±1, 33±3% of 14C-5HT release resulted. Aggregation induced by the PG endoperoxide analogue U46619 (lμM) was not inhibited by 300μM TSI or l00μM indomethacin, although 99.5% inhibition of Tx formation resulted, and 50 to 60% inhibition of 14C-5HT release was produced both by TSI and indomethacin. However CTA (l-3±M) produced a dose related inhibition of both aggregation and release induced by U46619. CTA (l-10μM) was found to produce superimposable dose related inhibition of collagen induced aggregation and secretion of platelets, whether the platelets were pretreated with 300μM TSI, or not.These results suggest that Tx formation is not necessary for human platelet aggregation, although is contributory to 14C-5HT release induced by collagen, adrenaline, AA and U46619.Also caution must be employed when CTA is used to elucidate the role of TxA2, as it appears to be an effective PG endoperoxide antagonist.

scholarly journals The Effect of Imidazole on Human Platelet Aggregation

Blood ◽  
1971 ◽  
Vol 38 (4) ◽  
pp. 417-421 ◽  
Author(s):  
JAMES W. DAVIS ◽  
PHYLLIS E. PHILLIPS
Keyword(s):  
Platelet Aggregation ◽  
Platelet Function ◽  
Glass Bead ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Second Phase ◽  
Platelet Function Tests ◽  
Human Platelet Aggregation ◽  
Function Tests ◽  
Induced Aggregation

Abstract Since imidazole buffers have been used in platelet function tests and the compound has been reported to alter several biochemical activities of platelets, it seemed important to determine whether imidazole influenced platelet aggregation. ADP-induced, collagen-induced, and norepinephrine-induced platelet aggregations were tested in platelet-rich plasma by turbidimetric techniques. Glass bead-induced platelet aggregation in whole blood was tested by a method dependent upon platelet counts. Imidazole, in concentrations of 5mM or less, inhibited aggregation induced by each of these four agents and had negligible effect on the pH of platelet-rich plasma. The second phase of both ADP- and norepinephrine-induced aggregation was inhibited or abolished by imidazole, and 5mM imidazole also inhibited the first phase of norepinephrine-induced aggregation. As little as 0.5 mM imidazole inhibited collagen-induced aggregation in some plasmas. Imidazole appears to be unsuitable for use as a buffer in platelet function tests.

Inhibition of Human Platelet Aggregation by a Dibenzazepine Compound (GP 44296) and by N-(2,6-dichlorophenyl)-o-aminophenylacetic acid(GP 45840)

1971 ◽  
Vol 49 (5) ◽  
pp. 479-481 ◽  
Author(s):  
François Jobin ◽  
France T. Gagnon
Keyword(s):  
Platelet Aggregation ◽  
Human Platelet ◽  
Secondary Phase ◽  
Human Platelets ◽  
Primary Phase ◽  
Human Platelet Aggregation ◽  
Induced Aggregation

Studies of the aggregation of human platelets indicate that compounds GP 44296 and GP 45840 inhibit the secondary phase of ADP-induced aggregation and collagen-induced aggregation; GP 44296 also inhibits the primary phase of ADP-induced aggregation. Our results suggest that these compounds are more active on platelet behavior in vitro than phenylbutazone, oxyphenbutazone, and sulfinpyrazone.

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