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Results for “Platelet Function Tests”

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At least 811 records · Page 45Linked to original sources
PubMed1984

[Primary thrombocyte reactions in hemostasis and thrombogenesis and the possibilities of influencing them by drugs].

The primary haemostasis begins with the activation of the thrombocytes. This activation is induced by nucleotides, by the haemostasis-activating factor existing in most tissues, by thrombin, collagen, adrenaline, serotonin and other activators. The activation is accompanied by an increased inclination of the thrombocytes to adhesion and aggregation. Morphologically activated platelets show appendices and become ball-shaped. These processes are reversible in vivo and in vitro. Medicaments inhibiting the function of the platelets were above all selected on account of their effect inhibiting the aggregation and were clinically tested. It is uncertain in what respect inhibition of the aggregation and inhibition of the thrombosis correlate. A technique for the judgement of the inhibition of the tissue extract-induced change of the form of thrombocytes is demonstrated as a method for the measurement of the activation of the platelets. Acetylsalicylic acid influences the aggregation of platelets by inhibition of the cyclooxygenase in the thrombocytes. This leads to an inhibition of the thromboxane synthesis in the platelets which lasts for days, since it is irreversible. The spontaneous change of the form of the thrombocytes and the tissue extract-induced change of the form of the platelets by acetylsalicylic acid are, however, influenced only for the duration of 6-10 hours.

Animals↗
PubMed1996

[Dysmegakaryocytopoiesis and dysthrombopoiesis in myeloproliferative syndromes].

Megakaryocyte proliferation in bone marrow is a feature common to the three Philadelphia negative chromosome myeloproliferative disorders (MPD)--essential thrombocythemia (ET), polycythemia vera, and myelofibrosis with splenic myeloid metaplasia--and chronic myelocytic leukemia. Enlarged megakaryocytes, clustering in close neighbouring with multilobulated nuclei are the hallmark of all the Philadelphia negative chromosome MPD. Clonality of hematopoietic cells, based on X-chromosome inactivation can now be studied in a majority of female patients in all nucleated cell fractions as well as in platelets. A significant increase in circulating CFU-MK has been repeatedly observed in MPD as well as a spontaneous megakaryocyte colony formation in a majority of ET patients. Hypersensitivity to thrombopoietin (TPO) in relation with a functional defect of the TPO-MPL pathway may play a major role in spontaneous megakaryocyte growth. There is presently no currently available test of platelet functions able to predict the risk of occurrence of thrombotic or haemorrhagic complications in MPD patients. However the role of platelets activation in the pathogenesis of ischemic erythromelalgia has been established.

Blood Platelets↗
PubMedDate not supplied

Increased releasability of platelet products and reduced heparin-induced platelet factor 4 release from endothelial cells in bronchial asthma.

To determine whether or not platelet activation is involved in the mechanism of exacerbation of bronchial asthma, we evaluated adenosine triphosphate (ATP) release from thrombin-stimulated washed platelets, plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4), and plasma beta-TG/PF4 ratios during symptomatic and asymptomatic periods in 15 patients with bronchial asthma compared with 16 normal control subjects. We also measured these parameters during allergen provocation tests and acetylcholine inhalation tests in 6 allergic asthmatics. ATP release, plasma levels of beta-TG and PF4 were significantly increased during symptomatic periods and after the allergen provocations but not after acetylcholine inhalations. However, these findings were not accompanied by the elevation of plasma beta-TG/PF4 ratios. The heparin-induced PF4 release, which is reported to reflect release of PF4 attached on endothelial cells, was significantly reduced in 12 asymptomatic asthmatic patients compared with 11 normal subjects, and it was much more reduced in 7 symptomatic asthmatic patients, suggesting the possibility of the reduced PF4 binding on endothelial cell surface. This finding may represent the prolonged half life of PF4 in asthmatics. We concluded that 1) increased releasability of platelet products and in vivo release of the platelet granular contents are involved in the mechanism of the exacerbation of bronchial asthma, 2) some functional alteration in platelet-endothelial cell interaction may be involved in bronchial asthma, and 3) plasma beta-TG/PF4 ratios are not elevated possibly because of both increased platelet releasability and prolonged half-life of PF4 in the blood in asthmatic patients.

Acetylcholine↗
PubMed2003

Influence of total intravenous and inhalational anaesthesia on haemostasis during tympanoplasty.

BACKGROUND: Surgical trauma leads to systemic changes in haemostasis. Haematological changes activated by surgery may become so prominent that changes caused by anaesthesia might be hidden or underestimated. Therefore, we have undertaken a prospective study to compare the behaviour of selected factors involved in the coagulation and fibrinolytic systems. METHODS: Forty healthy adult patients scheduled for otological surgery were enrolled in the study. Upon receiving informed consent, they were randomly assigned to receive either inhalational (IA) or total intravenous anaesthesia (TIVA). Platelet function (PFA100TM), disseminated intravascular coagulopathy (DIC) panel, and generalized d-dimer (GFC) were studied during certain periods of anaesthesia to identify the changes in haemostasis. RESULTS: Statistically, no significant change in DIC parameters were encountered between the two groups. No statistical difference was found between the two groups in the measured coagulation parameters, but statistically GFC showed slight activation in the 1st hour of surgical intervention. CONCLUSION: Presuming a minimal traumatic effect of surgical procedure on the determined variables, we conclude that different anaesthetic techniques have a negligible effect on platelet activation and fibrinolysis. The clinical relevance of coagulation activation and fibrinolysis during different anaesthetic techniques remains to be investigated.

Adult↗
PubMed1993

Depth-dependent change in membrane fluidity by phenolic compounds in bovine platelets and its relationship with their effects on aggregation and adenylate cyclase activity.

The effects of phenolic compounds on membrane fluidity of bovine blood platelets were investigated by studies on the fluorescence anisotropies of diphenylhexatriene (DPH) and its ionic derivatives to clarify the relationship of these effects with the inhibitory effects of the compounds on aggregation. Among the phenolic compounds tested, monohydric phenols (phenol and two monosubstituted derivatives) decreased the fluorescence anisotropy of DPH, which is thought to be located within the hydrophobic core of the membrane, in concentration ranges in which they inhibited platelet aggregation. On the other hand, they had little or no effects on the fluorescence anisotropies of the ionic derivatives of DPH, which are thought to be located in the interfacial region of the lipid bilayer. Consistent with their effects on the fluorescence anisotropy of DPH, these monohydric phenols increased the intracellular cAMP concentration. Thus, these monohydric phenols may inhibit platelet function by stimulation of adenylate cyclase mediated by perturbation of the central region of the membrane lipid bilayer. On the other hand, pyrocatechol and pyrogallol, which have two and three phenolic hydroxyl groups and have much larger electron donor activities than the monohydric phenols tested, inhibited platelet function by a different mechanism, because they did not cause increase in either membrane fluidity or the cAMP concentration of platelets.

Animals↗
PubMed1990

Circulating platelet activation in healthy subjects and in some pathological conditions. Method of study and results.

Current clinical methods for evaluating platelet function are artful tests which study the effects of various stimuli on platelets, whereas the clinician is much more interested in methods evaluating the activation of circulating platelets. The hallmark of activation of platelets is their shape change, i.e. the transformation of the platelets from smooth disks into spiny spheres; the aggregation begins when 30% of platelets are activated. In 1138 subjects (384 healthy individuals and 854 patients with various pathological conditions with high thrombotic risk) we have investigated circulating platelet activation and circulating platelet aggregates by fixation of blood cells in a glutaraldehyde mixture and by evaluation of platelet shape change and aggregates on a phase-contrast microscope. The method is precise, accurate and suitable for clinical purposes.

Adult↗
PubMed2000

Comparative study of antithrombotic effect of a low molecular weight heparin and unfractionated heparin in an ex vivo model of deep arterial injury.

Thrombosis after plaque rupture triggers the onset of acute coronary events. The treatment of choice for patients with acute coronary syndromes is conventional unfractionated heparin. Low molecular weight heparin has recently been reported to be as effective and even safer than unfractionated heparin. In this study, the effects of the low molecular weight heparin reviparin and unfractionated heparin on thrombus formation were examined under dynamic conditions using an extracorporeal perfusion chamber in a porcine model. Thrombus formation was assessed by the deposition of porcine 123I-fibrin(ogen) and autologous 111In-platelets on porcine tunica media at high and low shear rates. Reviparin reduced the fibrinogen molecules deposited on injured vessels at high shear rates (252+/-80 molecules x 10(12)/cm2 for reviparine (200 U/kg/hour) vs. 624+/-70 x 10(12)/cm for unfractionated heparin (200 U/kg/hour) (p<0.05). At low shear rates, fibrinogen deposition was also significantly reduced by reviparin (130+/-15 molecules x 10(12)/cm2) compared to unfractionated heparin (192+/-40 x 10(12)/cm2 at 200 U/kg/hour; p<0.05). No change in platelet deposition was detected after heparin administration in either treatment group. In conclusion, the low molecular weight heparin reviparin has a higher antithrombotic potential than unfractionated heparin. Reviparin may have advantages over unfractionated heparin in treatment and prevention of acute coronary syndromes.

Adenosine Diphosphate↗
PubMed1983

Tolerability of iohexol after injection into healthy volunteers.

The effects of iohexol, a new non-ionic contrast medium, after intravenous injection into humans are reported. After injection of small doses into 2 subjects, iohexol was injected intravenously into 20 healthy male volunteers in doses of 125 to 500 mg I/kg body weight. A large number of physiologic, biochemical, hematologic and pharmacokinetic parameters were analysed. The results indicated that iohexol was well tolerated and that clinical trials in patients could be undertaken.

Adult↗
PubMed1988

The in vitro and ex vivo antiplatelet effect of TRK-100, a stable prostacyclin analog, in several species.

Effect of TRK-100, a stable PGI2 analog, on platelet function was tested in vitro and ex vivo. TRK-100 at the dose range of 0.5-300 nM inhibited platelet aggregation induced by arachidonic acid, adenosine 5'-diphosphate and collagen in several species including human platelets. The potency of TRK-100 was 1/2 to 1/5 that of PGI2. The effect was strong in human and cat platelets. In conscious rabbits and rats, oral TRK-100 at the dose range of 0.1-1 mg/kg inhibited ex vivo platelet aggregation up to 80% in the rat and 70% in the rabbit, and the effect lasted over 5 hr. However, in both species, the effect on blood pressure was minimal. In anesthetized rabbits, inhibition of platelet aggregation was the same level as in the conscious animal, but blood pressure depression was observed. Cyclic AMP levels of human platelets, 2 min after incubation, was elevated up to 2.4 microM/10(9) platelets by 100 ng/ml of PGI2 and 1.5 microM by 100 ng/ml of TRK-100. It was shown that TRK-100 has a potent antiplatelet effect both in vitro and ex vivo in many species through elevation of platelet cAMP. These results suggest that TRK-100 may be a potential oral antithrombotic drug.

Adenosine Diphosphate↗
PubMed1992

Mild bleeding disorders. A clinical and laboratory study.

OBJECTIVE: To investigate in-vitro haemostasis in subjects with symptoms suggesting a mild bleeding disorder. DESIGN: A prospective study in which an extensive range of in-vitro tests were applied unselectively. SETTING: Patients were referred from community-based practices and hospital outpatient services. PATIENTS: Ninety-three consecutive patients were examined. Hospital patients with severe illness were excluded. CLINICAL FEATURES: Patients presented with easy bruising (68%), epistaxis (12%), excessive operative bleeding (7%), menorrhagia (4%), haematuria (3%), dental bleeding (1%) and bleeding from other sites (5%). In no instance was the bleeding life threatening. OUTCOME MEASURES: Results of laboratory tests for patients presenting with the symptoms of a mild bleeding disorder were compared with the results for a healthy reference group. RESULTS: Abnormal results of in-vitro tests were found in 53% of the subjects. Thirteen per cent had a prolonged bleeding time, of whom the majority had abnormal results of other in-vitro tests. Von Willebrand's disease was diagnosed in 7% of patients, although only half of these had a prolonged bleeding time. CONCLUSIONS: Abnormal results of in-vitro tests were prevalent among subjects with symptoms of mild bleeding disorder. Easy bruising was as powerful a clue as any other bleeding manifestation to the presence of an abnormal in-vitro test result.

Bleeding Time↗
PubMed1980

High-resolution particle analysis--its application to platelet counting and suggestions for further application in blood cell analysis.

The characteristics of an instrument for high-resolution particle analysis in flow are discussed. It employs a combination of hydrodynamic focusing, fluid resistors, and electronic techniques to achieve precision and ease of use heretofore unobtainable in a moderate-cost clinical instrument. Its application to whole blood platelet counting is discussed, and suggestions are made for its possible application to a wide variety of blood cell measurements.

Animals↗