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At least 163 records · Page 9Linked to original sources
PubMed1977

Changes of adenine nucleotides content and release reaction of human blood platelets following gamma irradiation.

The aim of this work was to examine the effect of gamma irradiation on the energy metabolism and physiological functions of blood platelets. Blood platelets were irradiated with a 60Co-source in the range of 0.5--8.0 krad. Before and after irradiation, the free nucleotide content of platelets and the ability of platelets to perform their hemostatic functions (the release reaction with thrombin) were determined. The obtained results demonstrated that: 1. ATP, ADP and AMP content reached minimum values at 1.5--2.0 krad. 2. The ability of platelets to perform the release reaction correlates with the ATP level at doses of 1.5--2.0 krad. At higher doses (6.0--8.0) disturbances of the release reaction, indicating damage to the platelet plasma membranes, were observed.

Adenine Nucleotides↗
PubMed1996

[Phagocytic activity of blood platelets in patients infected with Giardia intestinalis].

Blood platelets take part in immune reactions of the organism, especially in anti-parasitic immunity. We conducted this study measuring the phagocytic activity of blood platelets. The experiments were done on 35 patients infected G. intestinalis. Diagnosis was supported on finding trophozoits in bile cysts and GSA-65 protein in feces. We have found some decrease of blood platelets count and the increase the percentage of phagocytic platelets. Our general conclusion is, the parasite is able to stimulate the phagocytic activity of blood platelets.

Adult↗
PubMed1976

Reduction of blood platelet serotonin levels in manic and depressed patients.

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple contrifugation in the medium of Na2-EDTA solution, and the loss of serotonin during collecting procedures was about 11%. The mean value of blood platelet serotonin levels in depressed patients was 594+/-288ng/mg platelet protein (+/- S.D.), which was significantly lower than that for normal controls, 780 +/- 253ng/mg protein (p less than 0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 580+/-152ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5-HTP with a maintenance dose of 300mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5-HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.

5-Hydroxytryptophan↗
PubMed1976

Reduction of blood platelet serotonin levels in manic and depressed patients.

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple centrifugation in the medium of Na2-EDTA solution, and the loss of serotonin during collecting procedures was about 11%. The mean value of blood platelet serotonin levels in depressed patients was 594 +/- 288 ng/mg platelet protein (+/- S.D.), which was significantly lower than that for normal controls, 780 +/- 253 ng/mg protein (p less than 0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 580 +/- 152 ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5-HTP with a maintenance dose of 300 mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5-HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.

Adjustment Disorders↗
PubMed1989

Whole blood platelet aggregation in uremic dogs.

Whole blood platelet aggregation responses to collagen, arachidonic acid, and adenosine diphosphate were determined by use of the impedance method in 22 dogs with serum urea concentrations greater than or equal to 20 mmol/L, which was attributable to renal disease, and in 25 healthy control dogs. The median changes in impedance for the control dogs were 23 ohms for collagen, 18 ohms for arachidonic acid, and 6 ohms for adenosine diphosphate. The median changes in impedance in uremic dogs were 25 ohms for collagen, 21 ohms for arachidonic acid, and 15 ohms for adenosine diphosphate. There were no significant differences in platelet aggregation responses to collagen, arachidonic acid, and adenosine diphosphate between uremic and control dogs. Hemorrhagic tendencies were not detected in uremic dogs by use of whole blood platelet aggregation. Results of this study suggest that platelet aggregation by use of the whole blood platelet aggregometer is not abnormal in uremic dogs, but does not exclude the possibility of a platelet aggregation defect undetected by the whole blood system.

Adenosine Diphosphate↗
PubMed1979

[Reversible endocytosis apparatus of the blood platelets].

The functioning of ganules of blood platelets participating in the reversible endocytosis reaction was investigated in rabbits. Eczocytosis was shown to be initiated by inducers of two types: proteolytic enzymes and compounds accumulated by the granules (biogenic amines, dyes, anesthetics and phenothiazines). Heparin inhibits thrombin-induced eczocytosis. During eczocytosis produced by accumulation of compounds by blood platelet granules, the cells lose their capacity for maintaining the aggregation state. The nature of blood platelet granules participating in the reversible endocytosis reaction is discussed.

Animals↗
PubMed1981

Effect of hypophysectomy and adrenalectomy on 5-hydroxytryptamine uptake by rat hypothalamic synaptosomes and blood platelets.

The effect of adrenalectomy and hypophysectomy on 5-HT uptake by rat platelets and hypothalamic synaptosomes taken from the same animal was studies. The experiments were performed 1-2 weeks after the operations of the shamoperations. After adrenalectomy a significant decrease of 25% in 5-HT uptake by platelets was noted. In synaptosomes there was a similar trend, but the decrease was not significant. After hypophysectomy a significant 25% decrease in 5-HT uptake was observed both in platelets and in synaptosomes. These results suggest that corticosteroid hormones might mediate adaptive changes of 5-HT uptake both in synaptosomes and in blood platelets. Blood platelets have been used as a peripheral model of serotoninergic nerve terminal in studies concerning physiology of monoamines systems. But the present results suggest that also in some pathological conditions changes in platelet biochemistry could reflect those in the CNS neurones.

Adrenalectomy↗
PubMed1984

[Possible regulatory importance of cellular sulfhydryl groups and reduction metabolic pathways for the activation of human blood platelets].

The activation of the blood platelets is the prerequisite for their participation in physiological and pathological intravasal processes. An aimed influence on the distinct functions of the blood platelets presumes an exact knowledge about course and regulation of the activation of the platelets. Investigations on glucose-6-phosphate-dehydrogenase-deficient platelets and on the effect of glutathione-oxidizing substances on normal platelets showed references to a regulatory significance of the cellular thiol/disulphide state in the process of activation. In this case particularly the arachidonic acid balance and the SH/SS-state of platelet proteins seem to be in close connection with reductive ways of metabolism.

Arachidonic Acids↗
PubMedDate not supplied

Inhibition of oxidative stress in blood platelets by different phenolics from Yucca schidigera Roezl. bark.

OBJECTIVE: We investigated the comparative effects of resveratrol (trans-3,4',5-trihydroxystilbene), trans-3,3',5,5'tetrahydroxy-4'-methoxystilbene, and yuccaols A and C isolated from the bark of Yucca schidigera on oxidative stress in resting blood platelets and blood platelets activated by different agonists (thrombin or thrombin receptor activating peptide). METHODS AND RESULTS: Tested phenolics (1-25 microgram/mL) reduced, to different degrees, the level of reactive oxygen species measured by the luminol-dependent chemiluminescence and changed the production of O(2)(-) measured by the reduction of cytochrome c in resting blood platelets. They also inhibited the generation of free radicals in blood platelets activated by thrombin (P < 0.05) or thrombin receptor activating peptide (P < 0.05). Treatment of platelets with resveratrol or yuccaols A and C at the concentration of 25 microgram/mL increased (statistically non-significant) the level of thiobarbituric acid reactive substances in these cells (P > 0.05), whereas trans-3,3',5,5'tetrahydroxy-4'-methoxystilbene and the alcohol yucca extract reduced lipid peroxidation in blood platelets (P < 0.05). CONCLUSIONS: Resveratrol and other phenolic compounds from the bark of Yucca schidigera inhibiting free radical generation in blood platelets may be beneficial in protecting against cardiovascular diseases when hyperactivity of platelets is observed.

Animals↗
PubMed2001

A lineage-restricted and divergent beta-tubulin isoform is essential for the biogenesis, structure and function of blood platelets.

BACKGROUND: Mammalian megakaryocytes release blood platelets through a remarkable process of cytoplasmic fragmentation and de novo assembly of a marginal microtubule band. Cell-specific components of this process include the divergent beta-tubulin isoform beta1 that is expressed exclusively, and is the predominant isoform, in platelets and megakaryocytes. The functional significance of this restricted expression, and indeed of the surprisingly large repertoire of metazoan tubulin genes, is unclear. Fungal tubulin isoforms appear to be functionally redundant, and all mammalian beta-tubulins can assemble in a variety of microtubules, whereas selected fly and worm beta-tubulins are essential in spermatogenesis and neurogenesis. To address the essential role of beta1-tubulin in its natural context, we generated mice with targeted gene disruption. RESULTS: beta1-tubulin(-/-) mice have thrombocytopenia resulting from a defect in generating proplatelets, the immediate precursors of blood platelets. Circulating platelets lack the characteristic discoid shape and have defective marginal bands with reduced microtubule coilings. beta1-tubulin(-/-) mice also have a prolonged bleeding time, and their platelets show an attenuated response to thrombin. Two alternative tubulin isoforms, beta2 and beta5, are overexpressed, and the total beta-tubulin content of beta1-tubulin(-/-) megakaryocytes is normal. However, these isoforms assemble much less efficiently into platelet microtubules and are thus unable to compensate completely for the absence of beta1-tubulin. CONCLUSIONS: This is the first genetic study to address the essential functions of a mammalian tubulin isoform in vivo. The results establish a specialized role for beta1-tubulin in platelet synthesis, structure, and function.

Animals↗
PubMed1989

[Effect of short-term hypoxia on blood platelet function tests of normal subjects].

We studied how smoking and hypoxia affected blood platelet functions. Eighteen normal subjects (ten nonsmokers and eight smokers) inspired 13% oxygen gas and underwent platelet function tests (blood platelet count, MPV, maximum platelet aggregation rate, plasma beta-TG, plasma PF-4) measured just before inspiration and 30 minutes and 60 minutes after inspiration of the gas. Four principal results were obtained. First, breathing room air, blood platelet count and maximum platelet aggregation rate of smokers were significantly increased compared to those of non-smokers. Second, platelet counts and MPV were not affected by hypoxia in either group. Third, the maximum platelet aggregation rate of smokers was significantly decreased by hypoxia. Fourth, in both groups, the plasma levels of beta TG and PF-4 were decreased 30 minutes after inspiration of the 13% oxygen gas. In non-smokers, 60 minutes after inspiration, these plasma levels recovered to the primary levels. Our study showed that blood platelet functions of normal subjects were affected by hypoxia, and the effects of hypoxia on these functions in these two groups were markedly different.

Adult↗
PubMed1977

The effect of phospholipase C on rat blood platelets in vivo.

Rat blood platelets were treated with phospholipase C in vitro or phospholipase C was injected i.v. to rats. In both cases its effect on the functions of the platelets in vivo has been studied. No change was found in primary bleeding time or in platelet survival. Treatment with phospholipase C gave a moderate reduction of ADP-induced platelet aggregation in the pulmonary circulation whereas the aggregation induced by thrombin was unchanged. Iv. injection of phospholipase C caused a rapid, very moderate and transient increase of 51Cr-activity in the lungs without concomitant overt respiratory distress. A moderate increase in 51Cr-activity was noted in liver and kidney 24 and 48 h after injection of phospholipase C. This may be caused by a slightly increased leakage of 51Cr-labelled material from the platelets during exposure to phospholipase C.

Adenosine Diphosphate↗
PubMed1987

Structural differences between blood-platelet tubulin and other mammalian tubulins.

Carboxymethylated pig blood-platelet tubulin subunits have been characterized by comparing their electrophoretic mobilities and two-dimensional tryptic peptide maps with those of tubulin subunits isolated from four other mammalian tissues. These were pig brain, pig lung, pig sperm and bovine kidney. In addition to the major blood-platelet alpha- and beta-tubulin subunits, minor alpha- and beta-components could be resolved on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The major blood-platelet beta-tubulin, as well as the minor brain beta 2-tubulin subunit, were clearly tissue specific. In both cases, their two-dimensional peptide maps contained unique heavily labelled peptides. Distinct peptide maps were also observed for the major blood-platelet alpha-tubulin subunit as well as for sperm tail alpha-tubulin, both of which were missing peptides (different in each case) that were present in all of the other alpha-tubulin maps. Under our conditions, a protein with a molecular weight of 70,000 and an isoelectric point of pH 6.4 co-purified with blood-platelet microtubules.

Animals↗
PubMed1984

Effect of acetylsalicylic acid on glutathione consumption and hexose monophosphate shunt during arachidonic acid induced stimulation of human blood platelets.

Aggregation of human blood platelets by exogenous arachidonic acid is accompanied by a powerful increase in the net flux through the hexose monophosphate shunt and a decrease of the level of reduced glutathione. When platelet cyclooxygenase is inhibited by acetylsalicylic acid diminution by about 60% of arachidonic acid induced flux through the hexose monophosphate shunt as well as lower initial decrease of the glutathione level are found. Investigations with other glutathione oxidizing agents as diamide or tertiary butyl hydroperoxide reveal that acetylsalicylic acid influences neither the activities of glutathione providing enzymes nor that of glutathione peroxidase which catalyzes glutathione consuming reactions in the arachidonic acid metabolism. Together with literature data the results point to a consumption of reduced coenzymes in both cyclooxygenase and lipoxygenase pathways in platelets.

Arachidonic Acid↗
PubMed1969

The accumulation of guanethidine by human blood platelets.

1. When human blood platelets were incubated aerobically in plasma containing 2 x 10(-7) to 10(-3)M radioactive guanethidine for 10 min to 6 hr, the drug was accumulated against a concentration gradient until concentration ratios (platelet/plasma) of up to 80:1 were obtained.2. The decline in rate of uptake after 3 hr appeared to result from a decrease in platelet viability, because accumulation was reduced by prolonged incubation before addition of guanethidine.3. Uptake was energy-dependent because it was inhibited by cold and ouabain.4. Sodium ions were essential for guanethidine uptake and retention of 5-hydroxytryptamine (5-HT).5. Accumulation was inhibited by 5-HT, desipramine, cocaine, dexamphetamine, bretylium, tyramine and noradrenaline; bethanidine, p-chlorophenylalanine and (-)-alpha-methyldopa were inactive.6. Guanethidine was tightly bound to platelets, only 10% being lost from labelled cells during 60 min incubation in drug-free plasma; but efflux was increased by addition of amphetamine.7. The binding sites for guanethidine seemed to be different from those for 5-HT since guanethidine accumulation was independent of 5-HT levels, and neither guanethidine uptake or release were affected by reserpine.8. Guanethidine was not metabolized by platelets or plasma in vitro.9. We consider that, if our results regarding uptake, binding and release of guanethidine are confirmed in vivo, and also found to apply to other pharmacologically active agents, then the eventual loss of a platelet-bound substance may increase pharmacological action by raising plasma levels.

Autonomic Agents↗
PubMed1983

Structural properties of myosin from the particulate fraction of human blood platelets.

Fractionation of human blood platelets has revealed that myosin, a contractile and mechanochemical protein, is present in both the soluble and particulate fraction. The aim of this study was to elucidate whether platelets contain more than one myosin isoform, especially in view of the fact that in other cellular systems (cardiac muscle, amoeba) several myosin isoenzymes were found. The particulate fraction was solubilized by Triton X-100, and the myosin was purified by the same procedure used for the cytoplasmic myosin. The final preparation contained, in addition to myosin, a 130-kDa polypeptide, which was observed also in myosin preparations obtained from the soluble fraction. The electrophoretic mobilities of the two myosins were identical under both dissociating and nondissociating conditions. Comparison of the molecular structure of the heavy chain of the two myosins by limited proteolysis with Staphylococcus aureus V8 protease showed that the proteolytic fragments of the two myosins were rather similar, with only minor alterations in the quantitative distribution of the products. Two-dimensional peptide mapping of the iodinated tryptic peptides of the myosin heavy chains indicated that at least one peptide is missing in the map of the particulate myosin, as compared to its soluble counterpart. According to the two-dimensional peptide map, the 130-kDa polypeptide seems to be a proteolytic fragment of the myosin heavy chain and most probably the rod portion of the molecule. The observed minor variations in the structure of myosins isolated from the soluble and the fractions of human platelets may reflect differences in their respective physiological functions.

Actomyosin↗
PubMed1984

[Participation of the IgE receptor in the toxicity of blood platelets against schistosomes].

Human blood platelets, incubated with the serum from patients with schistosomiasis or allergic asthma, became cytotoxic for schistosome larvae, in an allergen-specific mechanism linked to surface bound IgE on platelets. Cytotoxic factors, among which oxygen metabolites might be involved, were able to kill schistosomula through platelet-retaining filters. Flow cytometry showed that platelets bearing IgE receptors represented a subpopulation, the percentage of which significantly increased in patients with high levels of circulating IgE.

Asthma↗