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Inquinamento da metalli nelle acque acide dell'area mineraria di Genna Luas (Iglesias) destinata ad ospitare un impianto di smaltimento di scorie industriali
No full textDipyridamole potentiates the inhibition of platelet aggregation by aspirin (in human platelet rich plasma and whole blood).
No full textThis study investigates the influence of dipyridamole on platelet aggregation as evaluated by a single agonist or a pair of agonists in human platelet rich plasma and whole blood. Dipyridamole up to 30 microM was not found to influence the platelet aggregation of platelet rich plasma or whole blood; aspirin (100 microM), on the contrary, did inhibit platelet aggregation. The inhibition of platelet aggregation by aspirin could be reversed by using high concentrations of agonists or pairs of agonists. In this model dipyridamole inhibited platelet aggregation in both platelet rich plasma and whole blood in a dose-dependent fashion. Thromboxane A2 was less than 10% of controls in aspirin-treated PRP stimulated with low or high concentrations of collagen or with a pair of agonists. This study suggests that dipyridamole has direct antiplatelet activity in platelet rich plasma and whole blood when the cyclooxygenase pathway is blocked by aspirin
Role of hydroxyl radicals in the activation of human platelets
No full textPlatelets primed by exposure to subthreshold concentrations of arachidonic acid or collagen are known to be activated by nanomolar levels of hydrogen peroxide. We here demonstrate that this effect is mediated by hydroxyl radicals (OHzero) formed in an extracellular Fenton-like reaction. H2O2-induced platelet aggregation, serotonin release and thromboxane A2 productions were inhibited by OHzero scavengers and by the iron chelator desferrioxamine; hydroxyl radicals were detected directly by ESR measurements of the spin-trapped OHzero adduct. The role of OHzero was confirmed in experiments with exogenously added iron; free or EDTA-bound ferrous iron activated platelets in a process blocked by deoxyribose, mannitol or catalase, whereas ferric iron was without effect unless reductants were included. The activation by OHzero depended on concomitant release of arachidonic acid and was blocked by the phospholipase A2 inhibitors mepacrine and aristolochic acid, and by the Na+/K+ antiporter inhibitor ethylisopropylamiloride. In contrast, neomycin and staurosporin were without effects, indicating that phospholipase C and protein kinase C were not involved in the initial phase of activation. Neither radical formation nor arachidonic acid release was blocked by aspirin. In whole blood aggregation of platelets could be induced by H2O2 generated upon specific stimulation of neutrophils by N-formyl-methionyl-leucyl-phenylalanine; platelet activation and radical formation were blocked by the NADPH oxidase inhibitor diphenyliodonium as well as by catalase and mannitol. These results suggest that reactive oxygen species act as 'second messengers' during the initial phase of the platelet activation process
Reaction of dipyridamole with the hydroxyl radical.
No full textDipyridamole [2,6-bis-diethanolamino-4,8-dipiperidinopyrimido-(5,4-d)pyri midine], a well known platelet aggregation inhibitor, shows powerful hydroxyl radical scavenging activity by inhibiting OH.-dependent salicylate and deoxyribose degradation. Steady-state competition kinetics experiments with deoxyribose were carried out to evaluate the second-order rate constant for the reaction between hydroxyl radical and dipyridamole. OH. radicals were generated either by a Fenton-type reaction or by X-ray irradiation of water solutions. A second-order rate constant k(Dipyridamole + OH.) of 1.72 +/- 0.11 X 10(10) M-1 s-1 and of 1.54 +/- 0.15 X 10(10) M-1 s-1 was measured by Fenton chemistry and by radiation chemistry, respectively. Mannitol was used as an internal standard for hydroxyl radicals in steady-state competition experiments with deoxyribose. A rate constant K(Mannitol + OH.) of 1.58 +/- 0.13 X 10(9) M-1 s-1 and 1.88 +/- 0.14 X 10(9) M-1 s-1 was measured in the Fenton model and in the water radiolysis system, respectively. Both these rate constants are in good agreement with the published data obtained by the "deoxyribose assay" and by pulse radiolysis
Superoxide dismutase triggers activation of primed platelets
No full textSuperoxide dismutase (SOD) triggers activation of human platelets exposed to subthreshold concentrations of arachidonic acid and collagen. The subthreshold concentrations used are not able to activate platelets but "prime" platelets to be activated by SOD. The addition of SOD to arachidonic acid-or collagen-primed platelets induced aggregation, thromboxane A2 production, and release of [3H]serotonin. Superoxide dismutase does not have any effect on resting platelets and ADP-, thrombin-, calcium ionophore A23187-, PAF-, or U46619-stimulated platelets. Furthermore, superoxide dismutase-dependent platelet activation is fully prevented by catalase and/or aspirin, suggesting a role for H2O2 and the involvement of the cyclooxygenase pathway of arachidonic acid in such activation
Hydrogen peroxide as trigger of platelet aggregation.
No full textIn order to verify if H2O2 affects platelet function, platelet-rich plasma and human washed platelets were incubated with subthreshold concentrations (STC) of collagen or arachidonic acid or ADP and/or with 75-150-mu-M H2O2. While H2O2 alone did not affect platelet aggregation, it amplified platelet aggregation response in samples stimulated with STC of arachidonic acid and collagen but not in samples stimulated with STC of ADP. When platelets were preventively treated with aspirin, a cyclooxygenase inhibitor, the platelet activation by H2O2 was not observed. Thromboxane A2 (TxA2) was not produced by human washed platelets stimulated with STC of arachidonic acid, collagen or by H2O2 alone. On the contrary, when STC of agonists were tested on platelets supplemented with H2O2 an evident TxA2 production was seen. This effect was prevented by aspirin pretreatment or by the addition of catalase, an enzyme which destroys H2O2. This study suggests that H2O2 triggers the activation of platelets exposed to STC of collagen and arachidonic acid, via the cyclooxygenase pathway
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Inhibition by picotamide of thromboxane production in vitro and ex vivo.
No full textThe effect of picotamide on platelet function has been studied in vitro and ex vivo. Picotamide at micromolar concentrations inhibited platelet aggregation induced by ADP, arachidonic acid and collagen, and it also inhibited the production of thromboxane A2 (TxA2). Unlike aspirin, picotamide did not affect the synthesis of prostacyclin by blood vessels. In eight healthy subjects who took picotamide 1200 mg/d platelet aggregation and TxA2 production were inhibited. Picotamide appears to be an antiplatelet drug that reduces TxA2 synthesis without affecting cyclo-oxygenase activity
Superoxide anion and hydroxyl radical release by collagen-induced platelet aggregation - Role of arachidonic acid metabolism
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