MMP-2 inhibition prevents platelet activation in ischemia/reoxygenation conditions.

BACKGROUND: Platelets play a fundamental role in myocardial infarction and the pathogenesis of ischemia/reoxygenation (I/R) injuries. They contain matrix metalloproteinases (MMPs) that are involved in arterial thrombosis. The MMP inhibitor doxycycline has been shown to exert protective effects in I/R injuries involving various organs and mechanisms. OBJECTIVES: To explore the influence of doxycycline on platelet activation and MMP-2 activity during I/R. MATERIAL AND METHODS: Platelets isolated from the blood of healthy human volunteers were subjected to chemical I/R conditions. The study included aerobic controls (AERO), I/R platelets and I/R platelets pretreated with doxycycline (I/R+D). The concentration of doxycycline used was standardized to 10 µM. The analysis of platelet activation markers and platelet microvesicles (PMVs) was performed using flow cytometry. Adenosine diphosphate (ADP)-induced and collagen-induced aggregation, as well as MMP-2 activity and its concentration in platelets were evaluated. RESULTS: Doxycycline decreased the expression of activated glycoprotein IIb/IIIa on platelets (p = 0.043). Additionally, an increased expression of CD63 was observed in buffers containing PMVs after doxycycline administration (p = 0.043). The ADP-dependent aggregation of I/R platelets was significantly lower in comparison to AERO (p = 0.022). Furthermore, there was a stronger tendency of enhanced ADP-dependent aggregation in I/R platelets pretreated with doxycycline compared to platelets that underwent I/R without doxycycline. Higher MMP-2 activity was observed in I/R+D platelets compared to I/R platelets (p < 0.01). CONCLUSIONS: The inhibition of platelet MMP-2 by doxycycline attenuated platelet activation and protected platelets by preserving their aggregation ability.

N-Stearoylethanolamine Inhibits Integrin-Mediated Activation, Aggregation, and Adhesion of Human Platelets.

N-stearoylethanolamine (NSE), a lipid mediator that belongs to the N-acylethanolamine (NAE) family, has anti-inflammatory, antioxidant, and membranoprotective actions. In contrast to other NAEs, NSE does not interact with cannabinoid receptors. The exact mechanism of its action remains unclear. The aim of this study is to evaluate the action of NSE on activation, aggregation, and adhesion of platelets that were chosen as a model of cellular response. Aggregation of platelets was measured to analyze the action of NSE (10-6-10-10 M) on platelet reactivity. Changes in granularity and shape of resting platelets and platelets stimulated with ADP in the presence of NSE were monitored by flow cytometry, and platelet deganulation was monitored by spectrofluorimetry. In vivo studies were performed using obese insulin-resistant rats. Binding of fibrinogen to the GPIIb/IIIa receptor was estimated using indirect ELISA and a scanning electron microscopy (SEM). It was found that NSE inhibits the activation and aggregation of human platelets. Our results suggest that NSE may decrease the activation and subsequent aggregation of platelets induced by ristocetin, epinephrine, and low doses of ADP. NSE also reduced the binding of fibrinogen to GPIIb/IIIa on activated platelets. These effects could be explained by the inhibition of platelet activation mediated by integrin receptors: the GPIb-IX-V complex for ristocetin-induced activation and GPIIb/IIIa when epinephrine and low doses of ADP were applied. The anti-platelet effect of NSE complements its anti-inflammatory effect and allows us to prioritize studies of NSE as a potent anti-thrombotic agent. SIGNIFICANCE STATEMENT: N-stearoylethanolamine (NSE) was shown to possess inhibitory action on platelet activation, adhesion, and aggregation. The mechanism of inhibition possibly involves integrin receptors. This finding complements the known anti-inflammatory effects of NSE.

Coumarin Derivatives Inhibit ADP-Induced Platelet Activation and Aggregation.

Coumarin was first discovered in Tonka bean and then widely in other plants. Coumarin has an anticoagulant effect, and its derivative, warfarin, is a vitamin K analogue that inhibits the synthesis of clotting factors and is more widely used in the clinical treatment of endovascular embolism. At present, many artificial chemical synthesis methods can be used to modify the structure of coumarin to develop many effective drugs with low toxicity. In this study, we investigated the effects of six coumarin derivatives on the platelet aggregation induced by adenosine diphosphate (ADP). We found that the six coumarin derivatives inhibited the active form of GPIIb/IIIa on platelets and hence inhibit platelet aggregation. We found that 7-hydroxy-3-phenyl 4H-chromen-4-one (7-hydroxyflavone) had the most severe effect. In addition, we further analyzed the downstream signal transduction of the ADP receptor, including the release of calcium ions and the regulation of cAMP, which were inhibited by the six coumarin derivatives selected in this study. These results suggest that coumarin derivatives inhibit coagulation by inhibiting the synthesis of coagulation factors and they may also inhibit platelet aggregation.

Rumex acetosella Inhibits Platelet Function via Impaired MAPK and Phosphoinositide 3-Kinase Signaling.

OBJECTIVE: To examine the antiplatelet and antithrombotic activity of Rumex acetosella extract. METHODS: Standard light aggregometry was used for platelet aggregation, intracellular calcium mobilization assessed using Fura-2/AM, granule secretion (ATP release) by luminometer, and fibrinogen binding to integrin αIIbß3 detected using flow cytometry. Western blotting is carried out to determine the phosphorylation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/Akt signaling. RESULTS: Rumex acetosella displayed the ability to inhibit platelet aggregation, calcium mobilization, granule secretion, and fibrinogen binding to integrin αIIbß3. Rumex acetosella has also down-regulated MAPK and PI3K/Akt phosphorylation (all P<0.01). CONCLUSION: Rumex acetosella extract exhibits antiplatelet activity via modulating GPVI signaling, and it may protect against the development of platelet-related cardiovascular diseases.

A novel anti-platelet peptide (Z4A5) potential for glycoprotein IIb/IIIa inhibits platelet aggregation.

INTRODUCTION: Z4A5 is a novel peptide that inhibits platelet aggregation and formation of platelet thrombi, but the mechanism of its anti-platelet effects remains unknown. This study explores the anti-platelet effect and mechanism of Z4A5. METHODS: We investigated the anti-platelet activity of Z4A5 on platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA) and thrombin (TH) in human platelet-rich plasma (PRP). Fibrinogen and PAC-1 binding to glycoproteinIIb/IIIa (GPIIb/IIIa) were measured by flow cytometry. In addition, we investigated the integrin specificity of Z4A5 in attachment and detachment assays using human umbilical vein endothelial cells (HUVEC) and assessed the relative cell number using the MTT assay. RESULTS: In vitro, Z4A5 inhibited ADP-, AA- and TH-induced human platelet aggregation with IC(50) values of 0.46 ± 0.05 µM (n = 10), 0.23 ± 0.0 5 µM (n = 10) and 0.21 ± 0.02 µM (n = 10), respectively. Z4A5 inhibited fibrinogen, and PAC-1 bound to platelet GPIIb/IIIa with IC(50) values of 0.48 ± 0.07 µM (n = 8) and 0.63 ± 0.12 µM (n = 6), respectively. Z4A5 failed to inhibit α(V)ß(3) integrin-mediated HUVEC attachment to vitronectin and did not cause any significant detachment of HUVEC monolayer when compared with the controls. CONCLUSIONS: Z4A5 is a potential anti-platelet drug that inhibits fibrinogen binding to GPIIb/IIIa, but does not affect the structurally similar integrin α(V)ß(3).

C-terminal ADAMTS-18 fragment induces oxidative platelet fragmentation, dissolves platelet aggregates, and protects against carotid artery occlusion and cerebral stroke.

Anti-platelet integrin GPIIIa49-66 antibody (Ab) induces complement-independent platelet oxidative fragmentation and death by generation of platelet peroxide following NADPH oxidase activation. A C-terminal 385-amino acid fragment of ADAMTS-18 (a disintegrin metalloproteinase with thrombospondin motifs produced in endothelial cells) induces oxidative platelet fragmentation in an identical kinetic fashion as anti-GPIIIa49-66 Ab. Endothelial cell ADAMTS-18 secretion is enhanced by thrombin and activated by thrombin cleavage to fragment platelets. Platelet aggregates produced ex vivo with ADP or collagen and fibrinogen are destroyed by the C-terminal ADAMTS-18 fragment. Anti-ADAMTS-18 Ab shortens the tail vein bleeding time. The C-terminal fragment protects against FeCI3-induced carotid artery thrombosis as well as cerebral infarction in a postischemic stroke model. Thus, a new mechanism is proposed for platelet thrombus clearance, via platelet oxidative fragmentation induced by thrombin cleavage of ADAMTS-18.

The rationale for and comparisons of different antiplatelet treatments in acute coronary syndrome.

Fundamentally, acute coronary syndromes are platelet-centric diseases, resulting from platelet-rich thrombi that develop at the site of vessel wall injury. In addition to aggregation, platelets modulate a plethora of other important pathophysiologic processes, including inflammation and coagulation. Therefore, a primary goal of therapy in the acute setting should be treatment with agents that provide predictable and superior platelet inhibition to prevent further ischemic events that develop from unchecked high platelet reactivity. Translational research studies of patients undergoing percutaneous revascularization have clearly demonstrated that adverse thrombotic outcomes are associated with high platelet reactivity and the latter is now emerging as a potent measurable cardiovascular risk factor. The intensity of antithrombotic therapy is influenced by patient risk. In the highest risk patients with elevated cardiac biomarkers indicative of myonecrosis, current guidelines support the use of early therapy with glycoprotein IIb/IIIa inhibition, aspirin, and clopidogrel.

Distinct but critical roles for integrin alphaIIbbeta3 in platelet lamellipodia formation on fibrinogen, collagen-related peptide and thrombin.

Integrins are the major receptor type known to facilitate cell adhesion and lamellipodia formation on extracellular matrix proteins. However, collagen-related peptide and thrombin have recently been shown to mediate platelet lamellipodia formation when presented as immobilized surfaces. The aims of this study were to establish if there exists a role for the platelet integrin alpha(IIb)beta(3) in this response; and if so, whether signalling from the integrin is required for lamellipodia formation on these surfaces. Real-time analysis was used to compare platelet morphological changes on surfaces of fibrinogen, collagen-related peptide or thrombin in the presence of various pharmacological inhibitors and platelets from 'knockout' mice. We demonstrate that collagen-related peptide and thrombin stimulate distinct patterns of platelet lamellipodia formation and elevation of intracellular Ca(2+) to that induced by the integrin alpha(IIb)beta(3) ligand, fibrinogen. Nevertheless, lamellipodia formation on collagen-related peptide and thrombin is dependent upon engagement of alpha(IIb)beta(3), consistent with release of alpha(IIb)beta(3) ligand(s) from platelet granules. However, the requirement for signalling by the integrin on fibrinogen can be bypassed by the addition of thrombin to the solution. These observations reveal a critical role for alpha(IIb)beta(3) in forming lamellipodia on collagen-related peptide and thrombin which is dependent on its ability to function as an adhesive receptor but not necessarily on its ability to signal. These results suggest that integrins may play an important role in lamellipodia formation triggered by nonintegrin ligands in platelets and possibly in other cell types.

Evaluation of platelet function, a method comparison.

Platelet function can be studied using many different methods why it is of interest to understand how data from different assays relate to each other. In the present study we compare two methods suitable for screening purposes with two established although laborious methods, impedance aggregometry and platelet-rich plasma (PRP) aggregation. The alternative assays tested were: (i) exposure of active alphaIIbbeta3, in diluted whole blood and (ii) whole blood aggregation assessed by residual platelet counting. The fibrinogen receptor activation assay was found to have the lower variability, higher sensitivity to ADP, and higher signal to noise ratio compared with residual platelet counting. The sensitivity and response profile of the fibrinogen receptor activation assay and residual platelet counting were more similar to PRP aggregation than to impedance aggregometry, whereas impedance aggregometry displayed lower sensitivity to ADP. The two alternative assays correlated well with PRP aggregation as well as with each other. The fibrinogen receptor activation assay displayed the highest potency for AR-C69931MX, possibly due to a lower protein content compared with residual platelet counting. The two studied assays compare well with the more established assays, and are thus both good alternatives for platelet function testing and evaluation of new potential platelet antagonists.

Platelet aggregation inhibition blocks C-reactive protein and interleukin-6 (IL-6) elevation after the coronary angioplasty: effect of the -174 G/C IL-6 gene polymorphism.

C-reactive protein (CRP), interleukin-6 (IL-6), and the -174 GC IL-6 gene polymorphism were analyzed after coronary angioplasty in 50 patients, 25 of whom were treated with the glycoprotein IIb/IIIa platelet receptor inhibitor eptifibatide for 24 hours. It was found that glycoprotein IIb/IIIa inhibition significantly blocked postangioplasty CRP increases in all patients but blocked IL-6 increases only in patients carrying the -174 GG genotype.

Effects of tirofiban on acute systemic inflammatory response in elective percutaneous coronary interventions.

OBJECTIVE: In this study the effect of a specific glycoprotein IIb/IIIa inhibitor, tirofiban [which also has antiplatelet activity on acute systemic inflammatory responses (IR) during elective percutaneous coronary intervention (PCI)] was evaluated. PATIENTS AND METHODS: Patients with stable angina pectoris and similar baseline characteristics who angiographically had a single lesion in their coronary arteries with a PCI performed on that lesion were enrolled in the study. One group of patients (control group, n = 52) received 0.9% NaCl (15 mL/h for 24 h) and the other group (tirofiban group, n = 55) had tirofiban (10 microg/kg bolus infusion in 3 min and 0.15 microg/kg/min for 24 h) in addition to stenting without pre-dilatation. The effect of interventional procedure on levels of cardiac troponin T (cTnT) and several parameters of acute IR (leukocytes, fibrinogen, C-reactive protein, interleukin-1, interleukin-6, interleukin-8 and tumor necrotizing factor-alpha) was assessed on blood samples obtained from all patients before PCI and at pre-specified time points after PCI. RESULTS: During the follow-up after PCI, the number of patients becoming cTnT-positive (> 0.1 ng/mL) was greater in the control group [12 (23%) patients vs. 3 (5%) patients, p = 0.01]. However, both groups had changes (generally observed as elevations) in their levels of all inflammatory parameters during the study and C-reactive protein, interleukin-6 and tumor necrotizing factor-alpha levels were elevated significantly. Yet, no significant difference occurred between groups due to these changes in any phase of the study (p > 0.05). CONCLUSIONS: Based on the findings of this study, it was concluded that although tirofiban limits development of myocardial necrosis during elective PCI, it does not directly affect the acute systemic inflammatory responses.

Effect of synthetic peptides corresponding to residues 313-332 of the alphaIIb subunit on platelet activation and fibrinogen binding to alphaIIbbeta3.

The platelet integrin receptor alphaIIbbeta3 plays a critical role in thrombosis and haemostasis by mediating interactions between platelets and several ligands but primarily fibrinogen. It has been shown previously that the YMESRADR KLAEVGRVYLFL (313-332) sequence of the alphaIIb subunit plays an important role in platelet activation, fibrinogen binding and alphaIIbbeta3-mediated outside-in signalling. Furthermore, we recently showed that the 20-residue peptide (20-mer) alphaIIb 313-332, is a potent inhibitor of platelet aggregation and fibrinogen binding to alphaIIbbeta3, interacting with fibrinogen rather than the receptor. In an effort to determine the sequence and the minimum length required for the biological activity of the above 20-mer, we synthesized seven octapeptides, each overlapping by six residues, covering the entire sequence and studied their effect on platelet activation as well as fibrinogen binding to activated platelets. We show for the first time that octapeptides containing the RAD sequence are capable of inhibiting platelet aggregation and secretion as well as fibrinogen binding to the activated alphaIIbbeta3, possibly interacting with the ligand rather than the receptor. This suggests that the RAD sequence, common to all the inhibitory peptides, is critical for their biological activity. However, the presence of the YMES sequence, adjacent to RAD, significantly increases the peptide's biological potency. The development of such inhibitors derived from the 313-332 region of the alphaIIb subunit may be advantageous against the RGD-like antagonists as they could inhibit platelet activation without interacting with alphaIIbbeta3, thus failing to further induce alphaIIbbeta3-mediated outside-in signalling.

Combined effects of mild hypothermia and glycoprotein IIb/IIIa antagonists on platelet-platelet and leukocyte-platelet aggregation.

Endovascular cooling was assessed as a potential treatment for percutaneous coronary intervention in patients with acute myocardial infarction. Here we show that mild hypothermia: (1) inhibits platelet aggregation; (2) augments eptifibatide- and tirofiban- but not abciximab-induced inhibition of platelet aggregation; (3) increases the formation of adenosine diphosphate-induced leukocyte-platelet aggregates; and (4) diminishes the glycoprotein IIb/IIIa antagonist-induced decrease in leukocyte-platelet aggregates.

Glycoprotein Ib-mediated platelet activation. A signalling pathway triggered by thrombin.

Platelet activation by thrombin plays a major role in the development of haemostasis and thrombosis. Thrombin activates human platelets by cleaving the N-terminal region of G-protein-coupled protease-activated receptors (PARs). On the other hand, the platelet membrane glycoprotein GPIb acts as a thrombin-binding site and promotes platelet activation by low thrombin concentrations. We present here new evidence in favour of a thrombin receptor function for GPIb. We have selected conditions in which thrombin-GPIb interactions were enhanced by thrombin immobilization. Activation was studied independently of PAR cleavage by using active-site-blocked thrombin. We show that immobilized, proteolytically inactive thrombin induces platelet adhesion and spreading, dense granule secretion and integrin alphaIIbbeta3-dependent platelet-platelet interactions. The pathway must be dependent on GPIb because it is deficient in platelets from a patient with Bernard Soulier syndrome and inhibited by a monoclonal antibody to GPIb (SZ2) or by an excess of glycocalicin. Secreted ADP plays a major role in GPIb-dependent thrombin-induced platelet activation which is, in addition, regulated by cAMP concentration. Thrombin-induced GPIb-dependent platelet activation leads to tyrosyl phosphorylation of several proteins. Inhibition of platelet-platelet interactions and protein tyrosine phosphorylations by inhibitors of phosphatidylinositol 3-kinases and protein kinase C implies that activation of the latter are important steps of the GPIb-coupled signalling pathway triggered by thrombin.

Platelets: is aspirin sufficient or must we know how to pronounce abciximab?

Although vascular disease may present with symptoms that are representative of a focal exacerbation of atherosclerosis, it is inherently a systemic disease. Consequently, vascular surgeons must be capable of recommending to their patients pharmacologic approaches that will decrease future risk of cardiovascular-related morbidity and death. Antiplatelet treatments, in particular, have been shown to reduce future cerebrovascular and coronary events. Moreover, these medications have utility in maintaining peripheral vessel and graft patency after surgical bypass, endarterectomy, or percutaneous translumenal angioplasty. The future of optimal antiplatelet therapy will consist of strategies that block multiple platelet activation pathways simultaneously. Moreover, the use of directed antiplatelet medications promises more effective control of platelet physiology with a concomitant increase in safety. The authors review herein current recommendations for the use of aspirin, thienopyridines, and GP IIb/IIIa inhibitors in patients with peripheral vascular disease.

Morphine-potentiated agonist-induced platelet aggregation through alpha2-adrenoceptors in human platelets.

Morphine dose-dependently (0.6, 1, and 5 microM) potentiated platelet aggregation and ATP release stimulated by agonists (i.e., collagen and U46619) in washed human platelets. Furthermore, morphine (1 and 5 microM) markedly potentiated collagen (1 microg/ml) evoked an increase of intracellular Ca2+ mobilization in fura 2-AM loading human platelets. Morphine (1 and 5 microM) did not influence the binding of fluorescein isothiocyanate-triflavin to platelet glycoprotein IIb/IIIa complex. Yohimbine (0.1 microM), a specific alpha2-adrenoceptor antagonist, markedly abolished the potentiation of morphine in platelet aggregation stimulated by collagen. Moreover, morphine (0.6-5 microM) markedly inhibited prostaglandin E1 (10 microM)-induced cAMP formation in human platelets, and yohimbine (0.1 microM) significantly reversed the inhibition of cAMP by morphine (0.6 and 1 microM) in this study. Morphine (1 and 5 microM) significantly potentiated thromboxane B2 formation stimulated by collagen in human platelets, and yohimbine also reversed this effect of morphine in this study. In addition, morphine (1 and 5 microM) did not significantly affect nitrate production in human platelets. Morphine may exert its potentiation in platelet aggregation by binding to alpha2-adrenoceptors in human platelets, which leads to reduced cAMP formation and subsequently to increased intracellular Ca2+ mobilization; this, in turn, is followed by increased thromboxane A formation and finally potentiates platelet aggregation and ATP release.

Use of glycoprotein IIb/IIIa platelet inhibitors in peripheral vascular interventions.

With the expanding use of endovascular techniques for the treatment of peripheral vascular disease, consideration of glycoprotein IIb/IIIa receptor inhibitors to enhance the safety and efficacy of these procedures has increased. The scientific literature shows the benefits with the use of these agents in coronary vasculature interventions. However, data evaluating treatment with glycoprotein IIb/IIIa receptor inhibitors during peripheral vascular procedures is limited, with the vast majority of the trials investigating abciximab. With the varied vascular beds and end organs that may be affected by peripheral vascular intervention, the safety and efficacy may need to be studies for each area. The current literature ranging from carotid stenting to thrombolysis and mechanical thrombectomy for acute limb ischemia is reviewed, and recommendations are discussed on the use of these agents. The forthcoming results of controlled clinical trials should further clarify the clinical applications of these agents in peripheral vascular intervention.

Utilidad de los bloqueadores de los receptores plaquetarios IIbIIIa en síndromes coronarios agudos / Usefulness of the IIb- IIIa platelet receptor blockers in the acute coronary syndromes

Las manifestaciones clínicas de los síndromes coronarios agudos son un continuo entre la angina de pecho inestable e infarto agudo al miocardio (AIM) sin supradesnivel del segmento ST hasta el IAM con supradesnivel de ST y la muerte súbita. La trombosis coronaria y el rol que juegan las plaquetas en el síndrome coronario agudo son factores etiopatogénicos determinantes. Los procedimientos intervencionales coronarios pueden despertar igual respuesta vascular y plaquetaria. Los bloqueadores de los receptores plaquetarios IIbIIIa se han incorporado a los últimos años como un grupo de drogas alternativas que se suman al tratamiento convencional de los síndromes coronarios agudos en un subgrupo de pacientes. En nuestro medio los bloqueadores IIbIIIa disponibles son abciximab, tirofiban y eptifibatide. Existe un volumen creciente de estudios clínicos que se han publicado y se revisan en esta presentación. En términos generales durante la realización de procedimientos intervencionales coronarios el agente más estudiado es abciximab, con efectos benéficos comparativos superiores a tirofiban y eptifibatide administrado en forma previa o inmediatamente antes de la angioplastia (asociado o no a stent coronario) en pacientes que tienen riesgo de oclusión aguda por cuadro clínico o anatomía desfavorable. Eptifibatide con dosis de carga mayores ha demostrado resultados favorables en estudios recientes. En el grupo de pacientes con angina de pecho inestable e IAM sin supradesnivel del segmento ST, en quienes no se ha considerado una intervención angioplástica inmediata, tirofiban y eptifibatide representan una buena alternativa, especilmente para aquellos pacientes que demuestran ser refractarios a las medidas antiisquémicas habituales o tienen marcadores séricos, como troponina T e I elevados. Abciximab no está indicado en este contexto clínico

Mechanisms involved in agonist-induced hyperaggregability of platelets from normal pregnancy.

There is substantial evidence of increased platelet reactivity in vivo and in vitro during pregnancy. Platelet activation occurs in pregnancy with a risk of the development of preeclampsia. In this study, platelet behavior was studied during 28-40 weeks of gestation in a group of women who remained normotensive and a group of nonpregnant female controls. Platelet aggregation and ATP release stimulated by agonists (i.e. collagen and adenosine 5'-diphosphate) were markedly enhanced in washed platelets from pregnant subjects. Furthermore, the collagen-evoked increase in intracellular Ca(2+) ([Ca(2+)](i)) mobilization in fura-2-AM-loaded platelets was also enhanced in pregnant subjects. Moreover, the binding activity of fluorescein isothiocyanate-triflavin toward the platelet glycoprotein IIb/IIIa complex did not significantly differ between the nonpregnant and pregnant groups. In addition, the amount of thromboxane A(2) (TxA(2)) formation from pregnant subjects was significantly greater than that from nonpregnant subjects in both resting and collagen-activated platelets. On the other hand, prostaglandin E(2) formation in the presence of imidazole in either resting or arachidonic acid (100 microM)-treated platelets did not significantly differ between these two groups. The levels of cyclic AMP formation in both resting and prostaglandin E(1) (10 microM)-treated platelets from pregnant subjects were significantly lower than those in nonpregnant subjects. Nitric oxide production was measured by a chemiluminescence detection method in this study. The extent of nitrate production in either resting or collagen-stimulated platelets from pregnant subjects did not significantly differ from that of platelets from the nonpregnant group. We conclude that the agonist-induced hyperaggregability of platelets from normal pregnancy may be due, at least partly, to an increase in TxA(2) formation and a lowering of the level of cyclic AMP formation, which leads to increased [Ca(2+)](i) mobilization and finally to enhanced platelet aggregation and ATP release.

Uso dos antiagregantes plaquetários no acidente vascular encefálico isquêmico / Antiplatelet drugs theraphy in ischemic stroke

Os antiagregantes plaquetários têm papel definido na prevenção secundária e no tratamento dos acidentes vasculares encefálicos isquêmicos. O ácido acetilsalicílico permanece como droga de primeira escolha, sendo a mais segura e com maior tempo de estudo, além de ter o menor custo. Sua dose ideal permanece incógnita, sendo que doses entre 50 a 325 mg/dia apresentam efeitos similares em diferentes estudos. Tienopiridinas como clopidogrel e ticlopidina devem ser reservadas para pacientes intolerantes ou alérgicos à AAS, devido a seus parefeitos, menor tempo de estudo e maior custo. Não há evidências que suportem o uso dos inibidores das glicoproteínas IIb/IIIa, como abciximab, na doença vascular encefálica isquêmica. Havendo indicação de antiagregantes plaquetários, é fundamental que sejam utilizados o mais precocemente possível