[Transfusion of blood platelets].
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Blood Platelets↗
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Effect of cisplatin on lipid peroxidation in pig blood platelets.
The effect of cisplatin (cis-diamminedichloroplatinum II) on the activities of the blood platelet antioxidative enzymes (glutathione peroxidase, superoxide dismutase) as well as on the peroxidation of blood platelet lipids was investigated. Cisplatin was found to cause a significant inhibition of platelet free radical scavering enzyme activity and an increase of malonyldialdehyde levels in blood platelets incubated with cisplatin in vitro.
Animals↗
Free radical-induced inhibition of ATP diphosphohydrolase activity (EC 3.6.1.5) from rat blood platelets.
In the present report we demonstrate the in vitro effects of free radicals on an ecto-ATP diphosphohydrolase activity (apyrase, EC 3.6.1.5) from rat blood platelets. Rat blood platelets were exposed to an oxidant-generating system (H2O2/Fe2+/ascorbate) and the ATP diphosphohydrolase activity was inhibited. The enzyme inhibition was prevented by glutathione (GSH) and cysteine but not by trolox as a vitamin E analogue. The TBARS (thiobarbituric acid reactive substances) assay and the determination of sulphydryl groups indicate that the inhibition of the enzyme activity in resting platelets is not related to lipid peroxidation or to oxidation of sulphydryl residues. These results demonstrate the susceptibility of ATP diphosphohydrolase activity from platelets to free radicals and suggest that amino acid residues which are essential for the enzyme function are probably modified.
Animals↗
The sensitivity of human blood platelets to the aggregating agent ADP during different dietary sodium intakes in healthy men.
We have investigated the effect of varying sodium intake on the renin-angiotensin system, ADP-induced platelet aggregation in vitro, and blood 5-HT concentrations in 9 male volunteers. Systolic blood pressure was slightly reduced during a low sodium diet, whereas the diastolic pressure remained unchanged. Plasma renin activity and aldosterone concentration both fell significantly when sodium intake was increased; plasma angiotensin II concentration also fell, but not significantly. There was a significant fall in haematocrit after an increased sodium intake, but there was no change in the whole-blood platelet count after correcting for this. There were no significant changes in either total (i.e. PRP) or platelet 5-HT concentrations. The extent of platelet aggregation induced by 5 and 20 mumol.l-1 of ADP increased significantly when dietary sodium intake was increased. When compared with low or normal sodium intakes, lower concentrations of ADP were required to produce 50% of maximum aggregation after a high sodium intake. The 5-HT2 receptor antagonist ketanserin (1 mumol.l-1 in vitro) reduced the extent of aggregation induced by 5 mumol.l-1 ADP after the volunteers had taken a high sodium diet, whereas the angiotensin II receptor antagonist saralasin (1 nmol.l-1) increased the rate of aggregation after the low sodium diet. Thus, during a high sodium intake, human platelets become more sensitive to the aggregating agent ADP. It is possible that this effect is mediated via platelet 5-HT2 receptors, since ketanserin abolished the increase in salt-induced aggregation seen with 5 mumol.l-1 ADP.
Adenosine Diphosphate↗
Reduction of blood platelet monoamine oxidase activity in schizophrenic patients on phenothiazines.
A newly developed assay for monoamine oxidase (MAO) activity in blood platelets (serotonin used as substrate) was applied for the measurement of the enzyme activity in 76 schizophrenic patients. No significant reduction was found in the blood platelet MAO activity in a group of 33 untreated schizophrenic patients, as compared to that in the normal controls. Male patients revealed to have lower enzyme activity than females in the schizophrenic group, as we described previously in the normal subjects. Treatment with phenothiazines caused significant reduction of blood platelet MAO activity, while platelet serotonin content and platelet count appeared to be not affected by the drug treatment. The authors suggest that blood platelet MAO activity may be related to hormonal factors but not to psychiatric diagnosis of schizophrenia or constitution liable to schizophrenic illnesses.
Adolescent↗
The effect of green laser light irradiation on whole blood platelets.
BACKGROUND: Laser light irradiation is assumed to have biostimulating effect in various cell types. However, there is still a lack of information concerning response of blood platelets to laser light irradiation. METHODS: In our study we used flow cytometry to monitor the effect of a green Nd-YAG laser (532 nm, 30 mW) irradiation on platelet activation and the expression of activated GPIIbIIIa glycoprotein complex (fibrinogen receptor) of whole blood platelets stained with fluorolabelled monoclonal antibody PAC-1. Also the formation of platelet microparticles and aggregates in a population of whole blood platelets following such irradiation was evaluated. RESULTS: Effects of laser light on platelet activation and reactivity were significant over a wide range of applied energies (p<0.01). While low and medium laser light energies (18 and 54 J) increased platelet activation, the irradiation with a high-energy laser light (108 J) resulted in depressed platelet reactivity and attenuated platelet response to activators. In addition, laser light irradiation had significant influence on the formation of platelet microparticles in either resting (p<0.05) or ADP-activated (p<0.05) platelets, while no significant effect was observed in collagen-activated platelets. On the other hand, laser light irradiation significantly increased the formation of platelet aggregates both in resting (p<0.01) and agonists-activated (p<0.05) platelets. CONCLUSIONS: Our results clearly point that the laser light irradiation of blood platelets can trigger signal transduction, leading to platelet activation, as well as the gradual loss of natural platelet reactivity and platelets' ability to respond to activating agents.
Blood Platelets↗
Identification of D1-like dopamine receptors on human blood platelets.
Dopamine is able to inhibit the epinephrine-induced aggregation of human blood platelets, but the mechanism of action has not been elucidated. In this study we report that membranes from human blood platelets possess high affinity, saturable and stereoselective binding sites for the D1 dopamine receptor antagonist (3H) SCH 23390. (3H) SCH 23390 appeared to label a single class of binding sites with a Bmax of 18.6 +/- 1.6 fmol/mg protein and a KD of 0.8 nM. The potencies of different dopaminergic antagonists and agonists in displacing (3H) SCH 23390 from blood platelet membranes were similar to those obtained for striatal membranes. Unlike the classically defined D1 receptors, e.g. those in striatum, the D1 receptor sites on platelets appeared not to be coupled to the adenylate cyclase system, hence the term "D1-like". The D1 agonist SKF 38393 was more potent than dopamine in inhibiting platelet aggregation induced by epinephrine, and the effects of dopamine and SKF 38393 were prevented by SCH 23390. These results suggest that the inhibitory action of dopamine on the epinephrine-induced platelet aggregation is mediated through these D1-like receptors.
2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
Effect of melatonin on active transport of serotonin into blood platelets.
Previous research has demonstrated that the circadian rhythm of melatonin negatively correlates with that of the sensitivity of platelet serotonin uptake sites. Moreover, serotonin has been found to be a competitive inhibitor of melatonin binding to platelets. The goal of the present study was to investigate whether melatonin directly affects platelet serotonin transport. Blood samples from 12 healthy subjects were assayed for both serotonin transport into platelets. Active transport of serotonin (at a concentration of 10(-6) M) into blood platelets was measured in the presence of melatonin at physiological concentrations (10(-12) M to 2 x 10(-9) M) and high nonphysiological concentrations (2 x 10(-8) M to 2 x 10(-3) M). Melatonin inhibited serotonin uptake by blood platelets at the high concentrations only ( > 10(-5) M with IC50 value of 1.1 x 10(-3) M) and had no effect at physiological concentrations.
Adult↗
Attachment of cytoskeletons to cell membranes in human blood platelets as revealed by the quick-freezing and deep-etching replica method.
This study evaluated ultrastructures of cell membrane-cytoskeletal interactions in resting and activated human blood platelets. Some blood platelets were fixed with paraformaldehyde to inhibit activation and the others were activated with thrombin treatment. The replicas of inside-out cell membranes, cell membrane surfaces, and Triton shells were made by the quick-freezing and deep-etching replica method. A geometrical pattern consisting of main hexagons and partial pentagons was revealed to be formed with microfilaments which were attached laterally to cytoplasmic sides of cell membranes in resting platelets. After the activation, cytoskeletal meshworks in the cytoplasm were densely associated with cell membranes, and parallel microfilamentous bundles in filopodia were connected with small polygonal meshworks lying under the cell membrane. The cell membrane-cytoskeletal interactions are essential to keeping a discoid shape at the resting stage, and to changing the shape quickly after the activation.
Adult↗
[Separate transfusion of erythrocytes, leukocytes and blood platelets].
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Blood Platelets↗
Affinity isolation and characterization of immunoglobulin G Fc fragment-binding glycoprotein from human blood platelets.
Immune complexes bind to several eukaryotic cell types including human blood platelets through the Fc fragment of immunoglobulin (Ig) G. Utilizing immobilized Fc fragment of IgG enabled us to isolate from human blood platelets a glycoprotein of an apparent Mr = 255,000 which, upon reduction, dissociated into sub-units of an apparent Mr = 50,000. This Fc fragment-binding glycoprotein has an isoelectric point between pH 6.3 and 6.9 and is composed of 34% hydrophobic, 25% acidic, and 14% basic amino acids. The Fc fragment-binding glycoprotein was also isolated from human platelet membrane preparations and was unaffected by prior treatment of platelets with thrombin. Isolated Fc fragment-binding glycoprotein formed an in vitro complex with aggregated immunoglobulin G. These results suggest that the isolated Fc fragment-binding component may prove useful in studies concerning the functional role of glycoproteins as cellular receptors for the Fc fragment of IgG.
Antigen-Antibody Complex↗
Influence of the hormonal balance of late pregnancy on the active uptake of 5-hydroxytryptamine by human blood platelets.
The active uptake of 5-hydroxytryptamine (5-HT) was studied in vitro in the blood platelets of twelve pregnant women during their final two months of pregnancy. The control group consisted of twelve women who were, on average, four days post partum. No significant difference in the uptake of 5-HT by blood platelets was found between these groups. Thus, the rapid fall in blood estrogen and progesterone concentrations after parturition did not seem to influence the uptake of 5-HT in human blood platelets.
Adult↗
[Determination of the vasoconstrictive blood platelet factor (5-hydroxy-tryptamine) in preserved blood].
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Blood Platelets↗
GABA uptake by human blood platelets: effects of lithium and rubidium chlorides.
The methodologic and kinetic characteristics of GABA uptake by platelets were determined in blood platelets of volunteer donors. Extrapolation of a reciprocal plot indicate two uptake systems: a high affinity and a passive diffusion mechanism. When LiCl and RbCl were added in vitro, they had no effect on platelet GABA uptake. Our data suggest that platelet GABA and 5-HT uptake are carried out by different systems.
Adult↗
The effect of human chylomicron suspensions on the recalcification time of platelet-poor plasma: an effect due to blood platelets.
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Blood Coagulation↗
Fine structural localization of arylsulfatase B activity in the rabbit blood platelets.
Fine structural localization of arylsulfatase in the rabbit blood platelets has been investigated in this study. Among many cell organellae, reaction products were exclusively observed in the alpha granules of the platelets. Within the alpha granules, arylsulfatase activity appeared to localize in variable patterns, i.e. reaction products confined mainly at the peripheral region in many granules, while they deposited heavily throughout the granule matrices in some others. In a blood platelets, each alpha granule showed the different staining pattern which indicated more variable functional heterogeneity in the granules.
Animals↗
Contractile properties of actomyosin from human blood platelets.
Actomyosin was purified from human blood platelets and used to form threads via extrusion. A sensitive tensiometer was employed to measure isometric tension and velocity of isotonic shortening of the threads in the presence of MgATP. Using fully phosphorylated myosin, we obtained values for maximum isometric tension (Po) and maximum velocity of contraction (V max) that were similar to those reported for threads composed of skeletal muscle actomyosin. Po was found to be directly proportional to the level of phosphorylation of the 20,000-dalton myosin light chain. We also studied the effect of phosphorylation on superprecipitation of platelet actomyosin. Fully phosphorylated myosin produced rapid clearing and superprecipitation, while myosin with a low level of bound phosphate underwent rapid clearing but did not superprecipitate. We have concluded from these results that: 1) the interaction between platelet actin and myosin produces tension and motion that is similar to that produced by skeletal muscle actin and myosin and 2) phosphorylation of the 20,000-dalton myosin light chain in important in controlling the production of force by platelet actin and myosin.
Actomyosin↗
Cancer procoagulant and blood platelet activation.
The effects of cancer procoagulant (CP), cysteine protease (EC 3.4.22.26), on the pig blood platelet secretory process and platelet aggregation have been studied. The response of platelets to CP was compared with the response of these cells to thrombin. The obtained results show that blood platelets treated with CP (0.5, 1, 2.5, and 5 microg/ml, 2-30 min, 37 degrees C) released adenine nucleotides (P < 0.05) and proteins (P < 0.05). The secretion of compounds from blood platelets after incubation with CP does not correlate with the release of platelet lactic dehydrogenase activity (marker of cell lysis) into the extracellular medium. In comparison with thrombin action, CP stimulates secretory process to a smaller extent than thrombin alone. In the presence of CP, the thrombin action is suppressed (P < 0.05). We noticed that CP does not induce platelet aggregation.
Adenine↗