scholarly journals Inhibitory Effect of Ethanol Extract of Piper longum L. on Rabbit Platelet Aggregation through Antagonizing Thromboxane A2 Receptor

2007 ◽  
Vol 30 (7) ◽  
pp. 1221-1225 ◽  
Author(s):  
Masaya Iwashita ◽  
Masaki Saito ◽  
Yasunaga Yamaguchi ◽  
Ryoji Takagaki ◽  
Norimichi Nakahata
Keyword(s):  
Platelet Aggregation ◽  
Thromboxane A2 ◽  
Ethanol Extract ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Piper Longum ◽  
Thromboxane A2 Receptor

scholarly journals The inhibitory effects of exogenous arachidonic acid on rabbit platelet aggregation and the release reaction

Blood ◽  
1982 ◽  
Vol 60 (5) ◽  
pp. 1179-1187
Author(s):  
M Cattaneo ◽  
RL Kinlough-Rathbone ◽  
DW Perry ◽  
A Chahil ◽  
JD Vickers ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Thromboxane A2 ◽  
Nordihydroguaiaretic Acid ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
General Effect ◽  
Lipoxygenase Pathway ◽  
Free Arachidonic Acid

Although arachidonic acid causes rabbit platelet aggregation and the release of granule contents in suspensions of washed platelets when used in concentrations of approximately 50–300 microM, higher concentrations (500 microM) cause neither aggregation nor release. Suspensions of platelets from rabbits wee exposed to arachidonic acid (250 microM) for 15 min, allowed to recover in the presence of PGE1 for 30 min, washed, and resuspended; in some experiments, the platelets were treated with aspirin before being exposed to arachidonic acid. Aggregation of platelets pretreated with arachidonic acid was inhibited in response to ADP; this effect was greater with the non-aspirin- treated platelets and persisted for at least 4 hr after resuspension. The association of 125I-fibrinogen with the platelets as a result of ADP stimulation was also inhibited. Aggregation and release of granule contents in response to collagen and low concentrations of thrombin was inhibited, but the inhibition could be overcome by higher concentrations. Thrombin induced further release of granule contents from platelets exposed to arachidonic acid without pretreatment with aspirin. Platelets that had been exposed to arachidonic acid, either with or without pretreatment with aspirin, did not aggregate or undergo further release upon stimulation with arachidonic acid after they were washed and resuspended. Inhibition of the lipoxygenase pathway with eicosatetraynoic acid (ETYA) or nordihydroguaiaretic acid (NDGA) did not affect the inhibition caused by arachidonic acid, so it is unlikely that a product of this pathway is responsible for the inhibition. Mixing experiments indicated that the pretreated platelets did not form a thromboxane-A2-like activity, and that they were unresponsive to aggregation and release induced by products formed from arachidonic acid. Experiments with 3H-arachidonic acid showed that after 45 min of incubation with platelets, only 1.1% of the 3H-arachidonic acid remained as free arachidonic acid in the platelets. Although cyclic-AMP was slightly increased 1 min after the addition of arachidonic acid, the cyclic-AMP concentration was the same as that of control platelets after the platelets were washed and resuspended, indicating that increased cyclic-AMP is not likely to be responsible for the persistent inhibitory effect. Thus, the inhibitory effect of pretreatment with arachidonic acid is a general effect on responses to a variety of aggregating agents that act through different mechanisms, and the inhibition is not related to thromboxane-A2 formation. The possibility of membrane perturbation resulting in the unavailability of receptors may explain the persistent inhibitory effect, but the responsible reactions have not been identified.

scholarly journals The inhibitory effects of exogenous arachidonic acid on rabbit platelet aggregation and the release reaction

Blood ◽  
1982 ◽  
Vol 60 (5) ◽  
pp. 1179-1187 ◽  
Author(s):  
M Cattaneo ◽  
RL Kinlough-Rathbone ◽  
DW Perry ◽  
A Chahil ◽  
JD Vickers ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Thromboxane A2 ◽  
Nordihydroguaiaretic Acid ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
General Effect ◽  
Lipoxygenase Pathway ◽  
Free Arachidonic Acid

Abstract Although arachidonic acid causes rabbit platelet aggregation and the release of granule contents in suspensions of washed platelets when used in concentrations of approximately 50–300 microM, higher concentrations (500 microM) cause neither aggregation nor release. Suspensions of platelets from rabbits wee exposed to arachidonic acid (250 microM) for 15 min, allowed to recover in the presence of PGE1 for 30 min, washed, and resuspended; in some experiments, the platelets were treated with aspirin before being exposed to arachidonic acid. Aggregation of platelets pretreated with arachidonic acid was inhibited in response to ADP; this effect was greater with the non-aspirin- treated platelets and persisted for at least 4 hr after resuspension. The association of 125I-fibrinogen with the platelets as a result of ADP stimulation was also inhibited. Aggregation and release of granule contents in response to collagen and low concentrations of thrombin was inhibited, but the inhibition could be overcome by higher concentrations. Thrombin induced further release of granule contents from platelets exposed to arachidonic acid without pretreatment with aspirin. Platelets that had been exposed to arachidonic acid, either with or without pretreatment with aspirin, did not aggregate or undergo further release upon stimulation with arachidonic acid after they were washed and resuspended. Inhibition of the lipoxygenase pathway with eicosatetraynoic acid (ETYA) or nordihydroguaiaretic acid (NDGA) did not affect the inhibition caused by arachidonic acid, so it is unlikely that a product of this pathway is responsible for the inhibition. Mixing experiments indicated that the pretreated platelets did not form a thromboxane-A2-like activity, and that they were unresponsive to aggregation and release induced by products formed from arachidonic acid. Experiments with 3H-arachidonic acid showed that after 45 min of incubation with platelets, only 1.1% of the 3H-arachidonic acid remained as free arachidonic acid in the platelets. Although cyclic-AMP was slightly increased 1 min after the addition of arachidonic acid, the cyclic-AMP concentration was the same as that of control platelets after the platelets were washed and resuspended, indicating that increased cyclic-AMP is not likely to be responsible for the persistent inhibitory effect. Thus, the inhibitory effect of pretreatment with arachidonic acid is a general effect on responses to a variety of aggregating agents that act through different mechanisms, and the inhibition is not related to thromboxane-A2 formation. The possibility of membrane perturbation resulting in the unavailability of receptors may explain the persistent inhibitory effect, but the responsible reactions have not been identified.

Role of phosphoinositide 3-kinase β in platelet aggregation and thromboxane A2 generation mediated by Gi signalling pathways

2010 ◽  
Vol 429 (2) ◽  
pp. 369-377 ◽  
Author(s):  
Analia Garcia ◽  
Soochong Kim ◽  
Kamala Bhavaraju ◽  
Simone M. Schoenwaelder ◽  
Satya P. Kunapuli
Keyword(s):  
Platelet Aggregation ◽  
Critical Role ◽  
Thromboxane A2 ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
P2y12 Receptor ◽  
Functional Responses ◽  
Induce Platelet Aggregation ◽  
Erk Phosphorylation

PI3Ks (phosphoinositide 3-kinases) play a critical role in platelet functional responses. PI3Ks are activated upon P2Y12 receptor stimulation and generate pro-aggregatory signals. P2Y12 receptor has been shown to play a key role in the platelet aggregation and thromboxane A2 generation caused by co-stimulation with Gq or Gz, or super-stimulation of Gi pathways. In the present study, we evaluated the role of specific PI3K isoforms α, β, γ and δ in platelet aggregation, thromboxane A2 generation and ERK (extracellular-signal-regulated kinase) activation. Our results show that loss of the PI3K signal impaired the ability of ADP to induce platelet aggregation, ERK phosphorylation and thromboxane A2 generation. We also show that Gq plus Gi- or Gi plus Gz-mediated platelet aggregation, ERK phosphorylation and thromboxane A2 generation in human platelets was inhibited by TGX-221, a PI3Kβ-selective inhibitor, but not by PIK75 (a PI3Kα inhibitor), AS252424 (a PI3Kγ inhibitor) or IC87114 (a PI3Kδ inhibitor). TGX-221 also showed a similar inhibitory effect on the Gi plus Gz-mediated platelet responses in platelets from P2Y1−/− mice. Finally, 2MeSADP (2-methyl-thio-ADP)-induced Akt phosphorylation was significantly inhibited in the presence of TGX-221, suggesting a critical role for PI3Kβ in Gi-mediated signalling. Taken together, our results demonstrate that PI3Kβ plays an important role in ADP-induced platelet aggregation. Moreover, PI3Kβ mediates ADP-induced thromboxane A2 generation by regulating ERK phosphorylation.

Inhibitory Effect Of Exogenous Arachidonic Acid Or Linoleic Acid On Rabbit Platelet Aggregation And Release Reaction

1981 ◽  
Author(s):  
M Cattaneo ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Arachidonic Acid ◽  
Linoleic Acid ◽  
Platelet Aggregation ◽  
Cell Membrane ◽  
Platelet Function ◽  
Unsaturated Fatty Acids ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Lipoxygenase Pathway ◽  
High Concentrations

In contrast to other release-inducing agents (e.g. thrombin) arachidonic acid (AA) releases only 40-50% of amine storage granule contents and although low concentrations induce aggregation, high concentrations do not. Several theories have been proposed to explain these observations: 1) AA or its products inactivates the cyclo-oxygenase; 2) the products of AA increase platelet cAMP; 3) lipoxygenase products are inhibitory; 4) unsaturated fatty acids (UFA) perturb the cell membrane. Using washed rabbit platelets we examined the effect of AA on platelet function. In these experiments aspirin-treated platelets (ASA 5.5 mM) were exposed to AA (230 μM) for 15 min. and then to PGEj (10 μM) for 30 min. The platelets were then resuspended. These platelets did not aggregate to ADP (9 μM) and their response to thrombin (0.02-0.05 U/ml) was impaired in contrast to control, ASA-treated platelets not exposed to AA. Non-ASA-treated platelets exposed to AA (230 μM), deaggre- gated with PGE1, and then resuspended also did not aggregate in response to ADP (9 μM) collagen, AA (230 μM) or thrombin (0.02-0.05 U/ml). When platelets pretreated with ASA and AA were mixed 1:1 with normal platelets and the mixture stimulated with AA (230 μM), the AA-treated platelets did not release their granule contents whereas the normal platelets did. These results do not support the hypothesis- that the inhibitory effect of AA on platelet aggregation and release is primarily due to inhibition of cyclo-oxygenase or an increase in cAMP caused by AA products. It seems unlikely that inhibition by AA can be due to products of the lipoxygenase pathway, because the effect persists when the platelets are washed and resuspended. Similar results were obtained by incubating platelets with linoleic acid (230 μM). This evidence is compatible with the hypothesis that UFA can inhibit platelet function by perturbing the cell membrane. This effect may be related to changes in receptor availability.

The Endocannabinoid 2-Arachidonoylglycerol Regulates Platelet Function.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3904-3904
Author(s):  
Samantha Baldassarri ◽  
Alessandra Bertoni ◽  
Paolo Lova ◽  
Stefania Reineri ◽  
Chiara Sarasso ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Platelet Function ◽  
Cannabinoid Receptors ◽  
Thromboxane A2 ◽  
Human Platelets ◽  
Dependent Manner ◽  
Cb2 Receptor ◽  
Thromboxane A2 Receptor

Abstract 2-Arachidonoylglycerol (2-AG) is a naturally occurring monoglyceride that activates cannabinoid receptors and meets several key requisites of an endogenous cannabinoid substance. It is present in the brain and hematopoietic cells, including macrophages, lymphocytes and platelets. 2-AG is released from cells in a stimulus-dependent manner and is rapidly eliminated by uptake into cells and enzymatic hydrolysis in arachidonic acid and glycerol. 2-AG might exert a very fine control on platelet function either through mechanisms intertwining with the signal transduction pathways used by platelet agonists or through mechanisms modulating specific receptors. The aim of this study was to define the role of 2-AG in human platelets and characterize the mechanisms by which it performs its action. Platelets from healthy donors were isolated from plasma by differential centrifugations and gel-filtration on Sepharose 2B. The samples were incubated with 2-AG (10–100 μM) under constant stirring in the presence or absence of various inhibitors. Platelet aggregation was measured by Born technique. We have found that stimulation of human platelets with 2-AG induced irreversible aggregation, which was significantly enhanced by co-stimulation with ADP (1–10 μM). Furthermore, 2-AG-dependent platelet aggregation was completely inhibited by ADP scavengers, aspirin, and Rho kinase inhibitor, as well as by antagonists of the 2-AG receptor (CB2), of the ADP P2Y12 receptor, and of the thromboxane A2 receptor. We further investigated the role of endocannabinoids on calcium mobilization. Intracellular [Ca2+] was measured using FURA-2-loaded platelets prewarmed at 37°C under gentle stirring in a spectrofluorimeter. 2-AG induced rapid increase of cytosolic [Ca2+] in a dose-dependent manner. This effect was partially blocked by ADP scavengers and CB2 receptor antagonists. Furthermore, 2-AG-induced [Ca2+] mobilization was totally suppressed by aspirin or the thromboxane A2 receptor antagonist. These results suggest that 2-AG is able to trigger platelet activation, and that this action is partially mediated by CB2 receptor and ADP. Furthmore, 2-AG-dependent platelet activation is totally dependent on thromboxane A2 generation.

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