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At least 595 records · Page 33Linked to original sources
PubMed1990

Malondialdehyde formation by blood platelets: a diagnostic test to assess acetylsalicylic acid induced thrombocytopathy?

We investigated whether the measurement of N-ethylmaleimide stimulated malondialdehyde (MDA) formation by blood platelets from normal subjects is equally sensitive to acetylsalicylic acid intake as are platelet aggregation studies. MDA production and platelet aggregation by collagen and arachidonate were assayed in ten healthy volunteers before and up to ten days after a single oral dose of 500 mg aspirin. Discordant results of the two tests were seen in several subjects 4 to 6 days after aspirin intake. In three cases with still suppressed MDA values on day 4, collagen or arachidonate induced aggregation was normalized. However, on day 6, when MDA was normalized in all subjects, the aggregation response to arachidonate was still pathologic in 5 of the ten volunteers. In case of a patient with abnormal aggregation response to arachidonate and/or collagen, therefore, a normal MDA value does not permit to exclude aspirin as the cause of the platelet dysfunction.

Adult↗
PubMed1995

Kinetic characterization of a carrier-mediated transport system for L-tryptophan in human blood platelets.

We have characterized a membrane transport system on washed human blood platelets for tritiated L-tryptophan (L-TRP). This transport was extremely rapid, temperature dependent and markedly reduced by disruption of the platelet membranes. Kinetic studies within a large range of L-TRP concentrations have revealed the presence of a high affinity saturable transport system which follows simple Michaelis-Menten kinetics, with an apparent Km value of 10 microM and a Vmax of 200 pmol/min/10(8) cells. Platelet L-TRP accumulation was insensitive to changes in sodium concentrations and to the inclusion of ouabain in the incubation medium. Furthermore, uptake was unmodified by the presence of the metabolic inhibitor dinitrophenol, suggesting that it is mediated by facilitated diffusion. D-Tryptophan was a very poor inhibitor of L-TRP uptake. Transport was insensitive to serotonin and imipramine but was inhibited in a dose-dependent manner by L-tyrosine, L-phenylalanine and L-leucine, implying that it may be mediated by a system that is specific for aromatic and long chain amino acids. The results were compared to reports examining the L-TRP transport in other cell types.

Biological Transport↗
PubMed1992

5HT2 receptor-mediated function in depressed patients: investigation by measuring 5HT-induced shape change of blood platelets.

The 5HT-induced shape change (5HT-SC) of blood platelets, which had been suggested to reflect the 5HT2 receptor-mediated function of the central nervous system (CNS), was examined in patients with depression before or after antidepressant therapy. The degree of 5HT-SC did not differ between patients before treatment (n = 17) and healthy controls (n = 26). In patients after treatment (n = 12), in whom depression had been improved but drug therapy was continued, 5HT-SC in a concentration of 10(-5) M 5HT was observed more potently than that in healthy controls or untreated patients (p less than 0.05 and p less than 0.05, respectively). In 4 patients in whom 5HT-SC was measured before and after mianserin treatment, 5HT-SC increased after the treatment. These results suggest that the 5HT2 receptor-mediated function in the CNS may not be damaged in patients with depression, and that the 5HT2 receptor-mediated function in the CNS may be enhanced by antidepressants.

Adult↗
PubMed1986

Serotonin in the lung. Demonstration of a close correlation to blood platelet.

The dependency of a high level of serotonin (5-hydroxytryptamine, 5HT) in the lung on blood 5HT was examined. The whole lung excised from NOD/Shi mice (male, 8-12 week old) immediately after being sacrificed by cervical dislocation contained 2.86 +/- 1.21 micrograms/g of 5HT per wet tissue. This amount was much higher than that explained by the included blood which was estimated by the hemoglobin concentration in the lung extract. In order to decrease 5HT level in the blood, platelet was depleted by an exposure to gamma-ray. On the 10th day after the irradiation the amount of 5HT in the lung and blood decreased to about 3.1% and 1.5% of the respective normal values. The progressive decrease in 5HT in the lung and blood of the irradiated mice was prevented by the transplantation of normal bone marrow cells (10(7) cells/mouse). 5HT in the intestine did not change significantly. The correlation between 5HT in the excised lung and the number of platelets in the blood was statistically significant (correlation coefficient r = 0.61). The irradiated, platelet-deficient mice were incapable of accumulating serotonin in the lung, while normal mice increased the lung serotonin more than 3-fold, when high doses of 5HT were administered. The results indicated that the high level of 5HT in the dissected lung was closely related to platelet in the blood. A question remained where the majority of the measured 5HT was located in the lung tissue.

Animals↗
PubMed1995

Afaâcytin, an alpha beta-fibrinogenase from Cerastes cerastes (horned viper) venom, activates purified factor X and induces serotonin release from human blood platelets.

Afaâcytin, a proteinase with caseinolytic, arginine-esterase and amidase activities, was purified from the venom of Cerastes cerastes (horned viper) in two steps by gel filtration through Sephadex G75, then HPLC on carboxymethyl-cellulose. Afaâcytin has an isoelectric point of 6.25, and consists of two subunits, alpha and beta, which have the same apparent molecular mass (40,000) and are indistinguishable in the absence of reduction or/and deglycosylation. Subunit beta is constituted of two disulfide-linked polypeptidic chains, beta and beta'. The respective apparent molecular mass of the chains are 43,000 (alpha), 35,500 (beta) and 10,200 (beta') as determined by SDS/PAGE under reducing conditions. Both chains alpha and beta are N-glycosylated. The two chains have the same N-terminal sequence (20 residues) which is similar to those of other proteinases from snake venom. Susceptibility of afaâcytin to diisopropyl fluorophosphate and benzamidine indicates the presence of a serine and an aspartic (or glutamic) acid residues in the catalytic site. Ca2+ appears to be required for structural cohesion of the afaâcytin molecule. Afaâcytin exhibits alpha beta-fibrinogenase and alpha-fibrinase properties. It replaces missing factors VIII and IX in deficient plasmas, and activates purified human factor X into factor Xa. It releases serotonin from platelets and directly aggregates human (but not rabbit) blood platelets. Despite its thrombin-like characteristics, however, afaâcytin is not inhibited by plasmatic thrombin inhibitors. The procoagulant properties of afaâcytin therefore have potential clinical applications.

Amino Acid Sequence↗
PubMed1976

Subcellular localization of the heparin-neutralizing factor in blood platelets.

1. The distribution of the heparin-neutralizing factor (platelet factor 4, PF4) in subcellular organelles of blood platelets of rabbits and man was investigated. 2. In both species the organelles storing 5-hydroxytryptamine (5-HT storage organelles) contained only trivial amounts of PF4. 3. In contrast, the content of PF4 was highest in the subcellular fractions rich in alpha-granules. 4. In conclusion, PF4 is probably localized in the alpha-granules and therefore the platelets contain at least two types of organelles (5-HT organelles and alpha-granules) capable of releasing their contents in response to the same stimuli, such as exposure to collagen, thrombin, etc.

Animals↗
PubMed1982

Fluorescent labeling of blood platelets in vivo.

In rabbits, a clear microscopic image of individual, fluorescent blood platelets flowing in a mesenteric microvessel could be obtained over the whole cross-sectional area of the vessel, following an intravenous injection of a solution containing 5-15 mg of the fluorochrome Acridine Red. Most of the circulating platelets were labeled. Activation of the platelets by the injected dye was not seen. A fall in platelet count or hematocrit following injection did not occur. Electron microscopy revealed no gross ultrastructural changes. In vitro, the dye reduced platelet aggregation in a dose dependent way. In vivo, aggregation and adhesion of platelets as induced by laser injury or transection of an arteriole was observed in all cases, even following multiple injections of Acridine Red. Primary hemostatic plug formation times as measured in mesenteric arterioles were normal after the first and second injection of 5 mg Acridine Red, but prolonged after subsequent injections. Bleeding times as measured on the ear were prolonged following injection of 15 mg of the dye. It is concluded that this labeling procedure allows the study of the rheological behavior of the platelets in vivo. Whether this technique can also be used to study functional platelet behavior in vivo, needs further investigation.

Acridines↗
PubMed1986

3H-imipramine binding in blood platelets of schizophrenic patients.

3H-Imipramine binding was studied in the blood platelets of 51 unmedicated chronic schizophrenic patients. Univariate analyses of log-transformed data revealed that Bmax was significantly lower in schizophrenic patients than normal volunteers; Kd was nonsignificantly higher in the schizophrenics. A multivariate analysis of variance indicated the Kd and Bmax both differ significantly between normal controls and schizophrenic patients in the direction of increased Kd and decreased Bmax in the schizophrenics. These results indicate that decreased platelet imipramine binding is not specific for major depression.

Adult↗
PubMed2005

Resveratrol may reduce oxidative stress induced by platinum compounds in human plasma, blood platelets and lymphocytes.

Resveratrol (trans-3,4',5-trihydroxystilbene), a polyphenolic compound found in grapes and wine, has been shown to have anti-inflammatory, anti-oxidant, anti-tumor and anti-platelet activities. Using different methods, we show that resveratrol reduces oxidative stress induced by cisplatin (cis-diamminedichloroplatinum II) and selenium-cisplatin conjugate ([NH(3)](2)Pt(SeO(3)), Se-Pt) in human blood platelets, lymphocytes and plasma. Resveratrol decreased the production of 8-epi-prostaglandin F(2) (a biomarker of lipid peroxidation) in control blood platelets and platelets treated with platinum compounds (10 microg/ml), and markedly reduced activities of different anti-oxidative enzymes (glutathione peroxidase, superoxide dismutase and catalase) in these cells. A combined action of resveratrol and Se-Pt evoked a significant decrease of DNA damage (measured by comet assay) in lymphocytes compared with cells treated with Se-Pt only. Resveratrol also caused a distinct reduction of total anti-oxidant level in plasma after incubation with platinum compounds. Therefore, anti-oxidative activity of resveratrol may diminish oxidative stress and damage to cellular biomolecules (lipids, proteins and DNA) induced by platinum compounds.

Antineoplastic Agents↗
PubMed1982

Rheo-optical shape analysis of human blood platelets.

Alterations in rheo-optical signals obtained from suspensions of human blood platelets treated in various ways (drugs, storage in the cold, stirring, etc.) were monitored. A self-normalizing instrument measuring scattered light and relative amplitude of rapid oscillation of light intensity (noise level) at different angles was used. The following results have been obtained: 1. The light scattered at an angle of 40 degrees was decreased with considerable selectivity by pseudopod formation, if aggregation was inhibited. 2. The noise levels at 0 degree and 40 degrees were selectively diminished by the transition from the discoid to the spheroid shape of the platelets. 3. At 40 degrees but not at 0 degree, the noise level responded without delay and was not influenced by aggregate formation. Using this method alterations in platelet form, i.e. spheroid transformation and pseudopod formation, can be specifically and continuously monitored. In addition, the noise level at 40 degrees is a definite quantitative measure of the discoid state. This allows the determination of platelet activation without manipulations such as changes in stirring rates or addition of drugs.

Adenosine Diphosphate↗
PubMed1983

Correlation between MAO activity in blood platelets obtained by single and multiple centrifugations.

Monoamine oxidase (MAO) activity in human blood platelets isolated by a single centrifugation at 600g for 2 1/2 minutes, which isolates only 45-65% of total platelets, was highly correlated with the MAO activity in platelets isolated by a method which isolates essentially 100% of platelets (r = 0.95, p less than 0.01). These results indicate that the single centrifugation method, which isolates only a portion of platelets, gives a reliable estimate of MAO activity in the entire platelet population.

Blood Platelets↗
PubMed1981

Uremic 'toxins' and blood platelet carbohydrate metabolism.

The effect of various small and middle molecular substances on blood platelet glycolysis was studied in vitro. Creatinine inhibited glucose utilization only at a concentration of 30 mg/dl; no effect of urea was found. o-Hydroxyphenolic acid and guanidinosuccinic acid, which were supposed to interfere with platelet function, inhibited glucose utilization at concentrations found in plasma of patients with chronic renal failure (CRF). Inhibitor of glucose utilization (IGU) peptide of middle molecular weight was found to inhibit glucose utilization without affecting glycogenolysis or lactate production. No additive or potentiating effects were found when interaction of different substances was tested. The only exception was a potentiation of IGU action on platelet glucose utilization by creatinine at a concentration of 15 mg/dl. Impaired glucose metabolism caused by 'uremic toxins' may contribute to the pathogenesis of bleeding in CRF by affecting platelet function.

Blood Platelets↗
PubMed1998

Tec is involved in G protein-coupled receptor- and integrin-mediated signalings in human blood platelets.

Tec is a non-receptor type tyrosine kinase which is tyrosine phosphorylated and activated upon stimulation of hematopoietic cells with various cytokines. The role of Tec in G protein-coupled receptor- and integrin-mediated signalings has not been elucidated. We therefore investigated the regulation of Tec in human blood platelets. Tec was rapidly tyrosine phosphorylated in response to platelet agonists which activate G protein-coupled receptors such as thromboxane A2 analog (U46619), thrombin, and thrombin receptor activating peptide (TRAP). TRAP-induced phosphorylation in Tec was significantly reduced under the conditions which abrogate fibrinogen binding to GP IIb-IIIa and subsequent platelet aggregation. However, TRAP induced significant levels of the phosphorylation even under these conditions and also in thrombasthenic platelets which lack functional GP IIb-IIIa molecules, suggesting that activation of G-protein-coupled receptor causes the phosphorylation. To clarify whether integrin engagement by itself causes the phosphorylation in Tec, we examined the state of the phosphorylation in platelets activated by integrin engagement. Platelet adhesion to immobilized fibrinogen or collagen induced significant levels of the phosphorylation. Furthermore, Tec was translocated to cytoskeleton in response to TRAP in a manner dependent on platelet aggregation, suggesting that Tec can be a component of integrin-mediated signalings. These results collectively indicate that Tec is involved in G protein-coupled receptor- and integrin-mediated signalings in human blood platelets.

Actins↗
PubMed1984

Isolation and characterization of human blood platelet gelsolin.

A 90-kDa protein-actin stable complex was purified from blood platelets by a short and efficient procedure giving at the same time actin used in polymerization assays. 90-kDa protein free of actin was prepared from the complex by 8 M ureau treatment and renaturation. By its molecular mass, immunological cross-reactivity with macrophage gelsolin and its effect on G- and F-actin the 90-kDa protein appears as the platelet gelsolin.

Actins↗
PubMed1988

Mechanism of inhibition of cyclo-oxygenase in human blood platelets by carbamate insecticides.

Carbamates are a widely used class of insecticides and herbicides. They were tested for their ability to affect human blood platelet aggregation and arachidonic acid metabolism in platelets. (1) The herbicides of the carbamate type have no, or only little, influence up to a concentration of 100 microM; the carbamate insecticides, however, inhibit both aggregation and arachidonic acid metabolism in a dose- and time-dependent manner. (2) Carbaryl, the most effective compound, inhibits platelet aggregation and cyclo-oxygenase activity completely at 10 microM. The liberation of arachidonic acid from phospholipids and the lipoxygenase pathway are not affected, whereas the products of the cyclo-oxygenase pathway are drastically decreased. (3) By using [14C]carbaryl labelled in the carbamyl or in the ring moiety, it could be proved that the carbamyl residue binds covalently to platelet proteins. In contrast with acetylsalicylic acid, which acetylates only one protein, carbaryl carbamylates a multitude of platelet proteins. (4) One of the carbamylated proteins was found to be the platelet cyclo-oxygenase, indicating that carbaryl resembles in this respect acetylsalicylic acid, which is known to inhibit this enzyme specifically by acetylation.

Arachidonic Acid↗