Specific Desensitization Of Washed Rabbit Platelets By Paf-Acether And Derivatives

1981 ◽  
Author(s):  
C Lalau Keraly ◽  
M Tencé ◽  
F Heymans ◽  
J Benveniste
Keyword(s):  
Arachidonic Acid ◽  
Alkyl Chain ◽  
Synthetic Analog ◽  
Synthetic Compounds ◽  
Glycerol Moiety ◽  
Rabbit Platelets ◽  
Acetyl Group ◽  
Induced Aggregation ◽  
Aggregation Of Platelets ◽  
Very High

PAF-acether-aggregated rabbit platelets did not respond to a second challenge with the same agonist after their spontaneous disaggregation, but still aggregated in the presence of arachidonic acid (AA). When using 1 nM of PAF-acether in the first stimulation, aggregation in response to a second challenge with the same dose was nil. However, when 0.34 nM was used in the first step, aggregation in response to 0.64 nM PAF-acether was 59 96, as compared to control platelets. By contrast, aggregation of platelets pretreated with 1 nM PAF-acether was 72 % in the presence of 2.8 uM AA. Adding fibrinogen (0.34 mg/ml) before the second stimulation did not modify the desensitization pehnom- enon. Supernatants from platelets desensitized with 1 nM PAF- acether exhibited neither aggregating nor inhibitory activity. PAF-acether-induced desensitization could always be overcome, since aspirin-pretreated platelets first stimulated with 10 nM PAF-acether still aggregated with 100 nM of the same agonist, i.e. when using 100 times the amount which induced maximal aggregation. All our experiments were performed in the presence of ADP scavengers and, except for AA-induced aggregation, aspirin. We tested PAF-acether from 4 different cell origins and the semi-synthetic and synthetic compounds. Platelets were cross- desensitized towards PAF-acether from any source. Totally synthetic PAF-acether bearing aC,, alkyl chain at position 1 of the glycerol moiety desensitized platelets as well as the C.g synthetic analog. Lyso-PAF-acether (i.e. a compound lackifig tne acetyl group at the position 2 of the glycerol) (0.5-10.0 nM) and PAF-acether enantiomer (0.5-5.0 nM) neither aggregated nor desensitized platelets to PAF-acether. These results indicate that 1) PAF-acether from any source exhibit at least an identical active molecular site ; 2) the presence and the stereospecific position of the 2-acetyl group are critical for the interaction of PAF-acether with platelets, a result which could indicate the existence of a platelet acceptor (receptor) for PAF-acether. However, these postulated platelet membrane acceptors were never saturated even using very high amounts of the agonist.

Inhibition by Glaucocalyxin A of Aggregation of Rabbit Platelets Induced by ADP, Arachidonic Acid and Platelet-Activating Factor, and Inhibition of [3H]-PAF Binding

1992 ◽  
Vol 67 (04) ◽  
pp. 458-460 ◽  
Author(s):  
Zhang Bin ◽  
Long Kun
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Activating Factor ◽  
Northeastern China ◽  
Ethereal Extract ◽  
Ic50 Value ◽  
Rabbit Platelets ◽  
Ic50 Values ◽  
Induced Aggregation

SummaryGlaucocalyxin A is a new diterpenoid isolated from the ethereal extract of the leaves of Rabdosia japonica (Burm f) Hara var glaucocalyx (Maxim) Hara (Labiatae) collected in the northeastern China. When it was incubated with washed rabbit platelets, glaucocalyxin A inhibited ADP- or arachidonic acid-induced platelet aggregation with IC50 values of 4.4 μmol/1, 14.1 μmol/1 respectively. Glaucocalyxin A also inhibited PAF-induced aggregation of rabbit platelets which were refractory to ADP and arachidonic acid with an IC50 value of 13.7 μmol/1. Analysis of [3H]-PAF binding showed that glaucocalyxin A prevented [3H]-PAF binding to intact washed rabbit platelets with an IC50 value of 8.16 μmol/1, which was consistent with its inhibition of PAF-induced platelet aggregation.

Effects of Ethanol on Pathways of Platelet Aggregation In Vitro

1988 ◽  
Vol 59 (03) ◽  
pp. 383-387 ◽  
Author(s):  
Margaret L Rand ◽  
Marian A Packham ◽  
Raelene L Kinlough-Rathbone ◽  
J Fraser Mustard
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Secondary Phase ◽  
Primary Phase ◽  
Rabbit Platelet ◽  
Membrane Phospholipids ◽  
Rabbit Platelets ◽  
Induced Aggregation

SummaryEthanol, at physiologically tolerable concentrations, did not affect the primary phase of ADP-induced aggregation of human or rabbit platelets, which is not associated with the secretion of granule contents. Potentiation by epinephrine of the primary phase of ADP-induced aggregation of rabbit platelets was also not inhibited by ethanol. However, ethanol did inhibit the secondary phase of ADP-induced aggregation which occurs with human platelets in citrated platelet-rich plasma and is dependent on the formation of thromboxane A2. Inhibition by ethanol of thromboxane production by stimulated platelets is likely due to inhibition of the mobilization of arachidonic acid from membrane phospholipids, as ethanol had little or no effect on aggregation and secretion induced by arachidonic acid or the thromboxane mimetic U46619. Rabbit platelet aggregation and secretion in response to low concentrations of collagen, thrombin, or PAF were inhibited by ethanol. Inhibition of the effects of thrombin and PAF was also observed with aspirin-treated platelets. Thus, in addition to inhibiting the mobilization of arachidonate for thromboxane formation that occurs with most agonists, ethanol can also inhibit aggregation and secretion through other effects on platelet responses.

The Role of Prostaglandins in the ADP-Induced Aggregation of Rabbit Platelets Shown by the Use of 15-Hydroxyprostaglandin Dehydrogenase

1978 ◽  
Vol 39 (03) ◽  
pp. 725-732 ◽  
Author(s):  
Robert B Wallis
Keyword(s):  
Platelet Rich Plasma ◽  
Shape Change ◽  
Rabbit Platelet ◽  
Direct Role ◽  
Initial Shape ◽  
Rabbit Platelets ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

SummaryThe initial shape change and subsequent aggregation of platelets in citrated rabbit platelet-rich plasma caused by ADP in vitro was inhibited by 15-hydroxyprostaglandin dehydrogenase. This inhibition was NAD-dependent and was also seen when shape change and aggregation were initiated by sodium arachidonate or by collagen. The aggregation of gel-filtered rabbit platelets by thrombin was not, however, affected by removal of 15-hydroxyprostaglandins.Indomethacin was found to inhibit ADP-induced aggregation but at a concentration (250 μM) much higher than that required to inhibit collagen-induced aggregation. Moreover the platelet release reaction had not taken place 3 min after ADP stimulation. The direct role 15-hydroxyprostaglandin production in ADP-induced aggregation of rabbit platelets is proposed. The involvement of 15-hydroxyprostaglandins in platelet aggregation caused by other inducers is also discussed.

Epinephrine-Induced Aggregation of Rabbit Platelets Refractory to ADP

1985 ◽  
Vol 53 (03) ◽  
pp. 366-371 ◽  
Author(s):  
C Lalau Keraly ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Platelet Aggregation ◽  
Adrenergic Receptor ◽  
Fibrinogen Binding ◽  
Rabbit Platelets ◽  
Induced Aggregation ◽  
Aggregation Of Platelets

SummaryThe mechanisms involved in platelet aggregation induced by epinephrine are unclear. Although epinephrine does not aggregate washed rabbit platelets, platelets made refractory to ADP will aggregate in response to epinephrine in the presence of ADP. We have examined whether the mechanism(s) by which epinephrine induces aggregation of refractory platelets involves fibrinogen binding and Ca2+ association. With normal platelets, ADP causes aggregation, fibrinogen binding and Ca2+ association in a medium containing 0.2 mM 45Ca2+. After 3 min of incubation with ADP, fibrinogen dissociates from platelets, but 45Ca2+ does not. Epinephrine alone does not cause aggregation, fibrinogen binding or 45Ca2+ association. Platelets that are refractory to ADP do not aggregate and bind fibrinogen upon addition of ADP, but aggregate and bind fibrinogen in response to epinephrine, provided ADP is still present. These effects of epinephrine are mediated by the α-adrenergic receptor since they are blocked by phentolamine or verapamil and potentiated by propranolol. However, epinephrine-induced aggregation of platelets refractory to ADP does not involve further detectable increase in the amount of 45Ca2+ associated with the platelets.

Differential Inhibition of Arachidonic Acid Mediated Aggregation of Platelets by Branded and Generic Argatroban Preparations

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 5131-5131
Author(s):  
Christopher Aranda ◽  
Debra Hoppensteadt ◽  
Omer Iqbal ◽  
Bruce E Lewis ◽  
Jawed Fareed
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Activation ◽  
Serotonin Release ◽  
Final Concentration ◽  
Release Mechanism ◽  
Clinical Effects ◽  
Induced Aggregation ◽  
Aggregation Of Platelets ◽  
Inhibition Of Thrombin

Abstract Abstract 5131 Argatroban represents a parentral antithrombin agent which is used in the management of anticoagulation in heparin compromised patients. Its main mechanism of action is mediated via inhibition of thrombin and its generation. While its effect on platelet activation inhibition by thrombin have been reported, very little information on the effects of this drug on thromboxane formation and Arachidonic Acid mediated activation of platelets is available. Argatroban and its generic versions namely Slovastan, Argaron and Gartban, may modulate Arachidonic Acid mediated platelet aggregation and release processes. To test this hypothesis a branded version of Argatroban (Mitsubishi – Tanade, Tokyo, Japan) and three generic versions of Argatroban namely Slovastan, Gartban, and Slovastan were compared for their effects on Arachidonic Acid mediated aggregation of platelets in normal healthy male and female volunteers (and n = 4). Other agonists such as Epinephrine, Collagen, and ADP were also used. The effect of Arachidonic Acid on serotonin release was also measured using an Elisa technique for the measurement of serotonin. All of the generic and branded versions of Argatroban produce varying levels of the inhibition of the Arachidonic Acid mediated aggregation of platelets, ranging from the 24 to 36 percent in comparison to the control at a concentration of 1 mg/ mL (p value < 0.05). Interestingly all of the Argatrobans produced a relatively weaker inhibition of the Arachidonic Acid mediated aggregation of platelets 24–26 percent inhibition versus 36 percent at the final concentration of 1 mg/mL. No differences were noted in the aggregation profile of ADP, Collagen, and Epinephrine between the control and the Argatrboban at a final concentration of 1 mg /mL. No differences were noted between the generic and branded Argatroban on all of the other agonists induced aggregation. In the serotonin release assays, all of the generic and branded Argatroban produced a concentration dependent inhibition of serotonin release which was stronger with the branded version of Argatroban. These results indicate that besides the inhibition of thrombin Argatroban is capable of inhibiting platelet activation via other mechanisms. Moreover, the generic versions of Argatroban exhibit a weaker inhibition of Arachidonic Acid mediated platelet aggregation and release. These studies suggest that beside thrombin mediated aggregation Argatroban and its generic versions can modulate platelet activation and release reactions. Furthermore a difference is observed between the generic and branded product which may impact the safety inefficacy profile in these agents. Argatroban is used commonly in the management of patients with heparin induced thrombocytopenia where multiple mechanisms of platelet activation are contributory to the pathogenesis of this syndrome. Modulation of thrombanxane formation and platelet release mechanism by Argatroban may represent an additional mechanism of the clinical effects of this parentral antithrombin agent. Disclosures: No relevant conflicts of interest to declare.

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