摘要:

The dose-dependent induction of platelet aggregation, dense granule secretion and thromboxane formation by the divalent cation ionophores A23187 and ionomycin were compared in citrated platelet rich plasma (PRP), and measured simultaneously with the increases in cytosolic Ca2+levels in aequorin-loaded gel-filtered platelet (GFP). In citrated PRP, both ionophores induced similar extents of aggregation at comparable concentrations, whereas A23187 induced somewhat greater extents of secretion, and substantially greater extents of thromboxane B2(TxB2) formation, than ionomycin. When 5 mM EDTA or EGTA was added to PRP secretion and TxB2formation occurred only with A23187; ionomycin was inactive at all concentrations tested, up to 100 pM. In aequorin-loaded GFP containing 1 mM Ca2+, 1 mM EGTA or 2 mM EDTA, ionomycin as well as A23187 induced these platelet responses, but the concentration dose-response curve for ionomycin was shifted to the right by approximately one order of magnitude relative to that for A23187. Simultaneous measurements of the cytosolic Ca2+([Ca2+]1) increases induced by the two ionophores showed that the increases produced by ionomycin were consistently 2040% less than those induced by A23187 at all ionophore concentrations tested. Analysis of the extents of secretion and TxB, formation obtained in EDTA- or EGTA-containing systems as a function of the [Ca2+]1increases suggested that the data for both ionophores were described by the same [Ca2+]1dose-response curve, indicating that the decreased extents of these responses seen with ionomycin vs A23187 were due primarily, if not solely, to the lower [Ca2+], increases produced by ionomycin. Since ionomycin is theoretically capable of transporting twice as much divalent cation as A23187, these findings in platelets, together with similar findings in certain other cell systems, provide evidence that factors associated with the intracellular environment may differentially affect the abilities of A23187 and ionomycin to induce cellular responses and, more specifically, to release intracellular Ca2+stores.

ISSN:0953-7104    

DOI:10.3109/09537109509078472

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Cyclosporine A (CyA) is known to be associated with an increased risk of thrombotic complications, whereas FK 506 therapy is believed to cause vasculitis. The aim of the study was to evaluate platelet aggregation in platelet rich plasma (PRP) and in whole blood and ATP release in healthy volunteers. CyA added in different concentrations resulted in a dose-dependent enhancement in platelet response to different agonists in PRP, whereas FK 506 did not influence platelet aggregation when added at a concentration of 2 ng/ml. Preincubation with FK 506 at concentrations of 15 and 50 ng/ml significantly inhibited platelet response to serotonin and epinephrine. Preincubation with both CyA and FK 506 did not affect platelet aggregation either in PRP or in whole blood. CyA at every concentration studied resulted in dose-dependent enhancement in ADP-induced platelet aggregation in whole blood, whereas platelet responses to other agonists were found to be increased only with the highest concentration of CyA together with ATP release. FK 506 (50 ng/ml) resulted in a significant decline in platelet aggregation, whereas lower concentrations did not affect platelet aggregatory responses. Platelet hyperreactivity in response to CyA may contribute, at least in part, to the increased incidence of thrombosis events. Platelet effects of FK 506 in vivo are not yet known, whereas in vitro this drug seems to inhibit aggregation of normal human platelets.

ISSN:0953-7104    

DOI:10.3109/09537109509078473

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Hepoxilin-A3(Hx-A3) is produced by platelets in response to shear-stress. It has an antithrombotic effect on platelets. A low Hx-A3level may contribute to the high thrombogenic state that exists in patients with acute coronary syndromes. Since we have previously demonstrated that the regulatory volume decrease (RVD) of human platelets exposed to hypotonic solutions is controlled by Hx-A3it is possible that the RVD rate reflects Hx-A3activity. In this study, the RVD rate of platelets taken from a healthy control group (n=21) was compared to that of patients with chronic ischemic heart disease (n=23), acute ischemic heart disease (n = 24) and acute myocardial infarction (MI, n = 29). The RVD rate of the control group was significantly higher than the other three groups (P<0.001). The addition of 100 nM of Hx-A, to the platelets of eight patients with MI increased their RVD rate to that of the controls. Patients with diabetes mellitus or hypertension have the lowest RVD rates. Medications such as aspirin, heparin, and streptokinase did not affect the Hx-A3activity of platelets obtained from patients with ischemic heart disease. The results of the present study indicate that patients with acute ischemia may have a low level of platelet Hx-A3activity. This possible low level of Hx-A, activity may be associated with a failure to develop an antithrombotic reaction to the shear-stress forces generated during acute ischemia.

ISSN:0953-7104    

DOI:10.3109/09537109509078474

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

We recently showed that collagen-induced platelet aggregation (PA) is enhanced by adrenaline ex vivo following cardiopulmonary bypass in man. Collagen-induced PA is impaired following bypass and this may contribute to postoperative blood loss, and aspirin treatment may further aggravate bleeding. To determine the influence of aspirin on the proaggregatory action of adrenaline following bypass, we assessed the effect of aspirin on collagen-induced PA before and after bypass, and following adrenaline infusion after bypass. Using optical aggregometry and hirudinised platelet rich plasma, in non-aspirin-treated controls (n=6), collagen (1.0 pg/ml) induced PA (median amplitude; cm) was maximal before bypass (13.7) and impaired at 10 min after bypass (11.5, P=0.03). PA was inhibited by aspirin (1 mM) before bypass (7.2 vs 13.7, P=0.03), and following bypass in aspirin-treated controls (3.3 vs 11.5,P=0.03). In aspirin-treated patients given adrenaline after bypass (n = 6), PA before adrenaline was impaired to a similar extent as in aspirin-treated controls (2.4 vs 3.3), but was enhanced following intravenous adrenaline infusion (0.55-1.1 nmol kg−1min−1) for 3-10 min (5.2 vs 2.4, P=0.03), with no change in controls at 20 min post-bypass (4.1 vs 3.3). This study indicates that at normocalcaemia, adrenaline enhanced collagen-induced PA in aspirin-treated patients, despite impairment of PA, but only at a high concentration of collagen. These findings indicate that aspirin-treatment may further impair collagen-induced PA following bypass, by limiting the proaggregatory effect of adrenaline.

ISSN:0953-7104    

DOI:10.3109/09537109509078475

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Albumin is the major protein in plasma and possesses high affinity binding sites for fatty acids. Previous studies have shown that albumin interferes at various levels with the metabolism of arachidonic acid by stimulated human platelets. The aim of our study was to further characterise the effect of serum albumin on the release of arachidonic acid from platelet phospholipids and on the formation of thromboxane B2In washed prelabeled human platelets, stimulated with thrombin (0.5 U/ml), the presence of albumin in the incubation medium leads to an accumulation of [3H]AA in the extracellular space and to a reduced formation of thromboxane B2. In an albumin-free medium, the radioactivity of thromboxane B2is markedly greater, while that of arachidonate is much less. The effect of bovine serum albumin is dose-dependent (0.35%, 1.0% and 3.5%). These data suggest that arachidonic acid liberated by PLA2-activation is released to the extracellular space where it binds serum albumin and thus is no longer available for its metabolic conversion to thromboxane B2.

ISSN:0953-7104    

DOI:10.3109/09537109509078476

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

We previously reported that thrombin-induced Ca2+mobilization was enhanced in aged rat platelets. Since Ca2+mobilization in platelets is believed to be closely associated with platelet activation, we examined Ca2+mobilization and the aggregatory response to ADP and thrombin in young (3 months) and aged (24 months) rat platelets. Blood levels of fibrinogen and Ca2+in aged rats were higher than those in young rats. ADP-induced platelet aggregation in aged rats was significantly enhanced in platelet rich plasma and in washed platelet suspension, suggesting that age-associated hyperaggregability to ADP is attributable to changes in platelets themselves. On the other hand, thrombin (0.03-0.3 unit/ml)-induced aggregation in washed platelet suspension from aged rats was comparable to that from young rats. But, thrombin (0.3 unit/ml)-induced intracellular Ca2+mobilization was enhanced in aged rat platelets in the presence of extracellular Ca2+. Likewise, ADP-induced Ca2+mobilization was enhanced in aged rat platelets. These results suggest that enhanced Ca2+mobilization in aged rat platelets is associated with hyperaggregability to ADP but not to thrombin.

ISSN:0953-7104    

DOI:10.3109/09537109509078477

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The effects of varying concentrations of platelet-activating factor (PAF), arachidonic acid (AA) and collagen on the expression of the platelet activation markers CD63 and CD62P were assessed in 10 normal subjects using flow cytometry. CD63 expression was significantly greater than CD62P expression, with PAF (80 nM) inducing mean maximum CD63 expression of 32.9±6.4% and mean maximum CD62P expression of 5.5±1.8%. AA (1 mM) induced maximum CD63 expression of 37.7±7% and maximum CD62P expression of 9.3±1%. Collagen (2-80 pg/ml) induced minimal expression but 800 pg/ml induced mean CD63 expression of 33.1±4.1% and mean CD62P expression of 6.1±0.8%. Greater CD63 and CD62P expression were induced by phorbol myristate acetate (1.6 pM, 70.9±11% and 69.4±9.9%, respectively) and thrombin (0.1 U/ml, 70.7±9.3% and 73.5±5.4%, respectively). With PAF and collagen only one platelet population was detected whereas with 1 mM AA two populations were observed. These results indicate that expression of platelet adhesion receptors depends on the nature and concentration of agonist and that subpopulations of platelets may exist. Importantly, PAF concentrations inducing moderate CD63 and CD62P expression did not induce platelet aggregation, suggesting that platelets can be activated independently of aggregation.

ISSN:0953-7104    

DOI:10.3109/09537109509078478

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

This study was designed to investigate platelet aggregation, plasma thromboxane A, and prostacyclin concentration and platelet sensitivity to prostacyclin simultaneously during the first month after myocardial infarction (MI). Spontaneous platelet aggregation and aggregation responses to ADP and adrenaline were low on the day of admission, increased rapidly by the 7th day post-MI, remained elevated during the second week post-MI and reached the level of chronic coronary artery disease patients but not healthy persons at the end of the fourth week of illness. An increase in plasma thromboxane B, the spontaneous and stable breakdown product of thromboxane A, level and enhanced prostacyclin production, with a maximum on the third post-MI day, were observed. We also demonstrated a significant platelet resistance to prostacyclin in MI patients. Thrombocyte sensitivity to prostacyclin normalized by the end of the fourth post-MI week. These results indicate the need for therapy with platelet inhibitors in patients with MI.

ISSN:0953-7104    

DOI:10.3109/09537109509078479

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

In insulin-dependent diabetics (IDDM) and peripheral occlusive arterial disease (POAD), inhibition of platelet aggregation (PA) by PGI2and PGE1was reduced (p<0.02) compared with non-diabetics and POAD as well as with healthy subjects at a similar extent of PA (in the 3 groups). c-AMP content in resting platelets of IDDM and chronic renal failure was decreased (mean±SD in pmo1/2.5×108platelets): 5.3±1.1 compared with the content in healthy subjects: 8.0±1.12 andP<0.012. Moreover, c-AMP content in PGE1-stimulated platelets was also reduced in these patients. Our results indicate that diabetic patients are characteristically less sensitive to inhibition by the 2 prostanoids, presumably through attenuated activity of the c-AMP generating system.

ISSN:0953-7104    

DOI:10.3109/09537109509078480

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0953-7104    

DOI:10.3109/09537109509078481

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor