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At least 325 records · Page 18Linked to original sources
PubMed1995

Activity of platelet alpha-6-fucosyltransferase is inversely related to blood platelet concentration.

The activity of serum alpha-6-fucosyltransferase, a platelet derived enzyme, determined in sera of 22 normal individuals and 86 patients with various disorders was positively correlated with platelet counts. When the enzyme activity in 1 microliters serum was calculated per 1000 of platelets in blood (coefficient F/P) an inverse correlation became evident in that F/P was proportionally the higher the lower was platelet count in blood. The F/P values were in a good agreement with the results of direct assays of enzyme activities in isolated platelets. Neither granulocytes, lymphocytes nor red cells significantly contributed to serum enzyme activity though granulocytes enhanced the thrombin-induced enzyme release from platelets. In platelets separated by centrifugation in density gradients the enzyme was shown to be present in platelets of intermediate and high density but missing from the light ones. It is suggested that alpha-6-fucosyltransferase of platelets may be a marker of the ploidy level of megakaryocytes.

Blood Platelets↗
PubMed2006

Portable dynamic light scattering instrument and method for the measurement of blood platelet suspensions.

No routine test exists to determine the quality of blood platelet transfusions although every year millions of patients require platelet transfusions to survive cancer chemotherapy, surgery or trauma. A new, portable dynamic light scattering instrument is described that is suitable for the measurement of turbid solutions of large particles under temperature-controlled conditions. The challenges of small sample size, short light path through the sample and accurate temperature control have been solved with a specially designed temperature-controlled sample holder for small diameter, disposable capillaries. Efficient heating and cooling is achieved with Peltier elements in direct contact with the sample capillary. Focusing optical fibres are used for light delivery and collection of scattered light. The practical use of this new technique was shown by the reproducible measurement of latex microspheres and the temperature-induced morphological changes of human blood platelets. The measured parameters for platelet transfusions are platelet size, number of platelet-derived microparticles and the response of platelets to temperature changes. This three-dimensional analysis provides a high degree of confidence for the determination of platelet quality. The experimental data are compared to a matrix and facilitate automated, unbiased quality testing.

Blood Platelets↗
PubMed1992

Abnormalities in the regulation of blood platelet free cytosolic calcium in malignant hyperthermia. I. Human platelets.

The effect of halothane on the regulation of blood platelet free cytosolic calcium was investigated in Quin-2-loaded cells from patients susceptible to Malignant Hyperthermia (MH) and healthy controls, respectively. The resting level of free cytosolic calcium was slightly, but statistically significantly, enhanced in platelets from patients (90 +/- 10 nM vs 110 +/- 35 nM). Halothane induced a dose-dependent, rapid Ca2+ release from intracellular stores both in normal and in MH derived cells, but the resulting increase in cytosolic calcium was significantly higher in the latter (2 mM halothane: [Ca2+]i = 117 +/- 12 nM vs 218 +/- 117 nM; 4 mM halothane: 225 +/- 35 nM vs. 417 +/- 201 nM). Whereas in platelets from healthy donors a complete reversibility of the halothane effect could be observed within 30-45 min, the cytosolic Ca2+ transients in platelets from patients were different from those in normals either in a higher initial peak or in a diminished decline velocity or in both. The basal Ca2+ permeability of the platelet plasma membrane was very low. Generally, halothane caused a dose-dependent increase in Ca2+ permeability. However, the influx of external calcium was significantly higher in platelets from patients than in controls (2 mM halothane: delta [Ca2+]i = 69 +/- 12 nM vs 135 +/- 63 nM; 4 mM halothane: 127 +/- 33 nM vs. 258 +/- 111 nM). Combining the results, the suggestion can be made that susceptibility to MH is characterized by a generalized membrane defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Immunocytochemical localization of fibrinogen, platelet factor 4, and beta thromboglobulin in thin frozen sections of human blood platelets.

Affinity-purified monospecific antibodies against human fibrinogen and the platelet-specific proteins platelet factor 4 and beta thromboglobulin were used to localize these antigens in thin and ultra-thin frozen sections of mildly fixed, washed human blood platelets. By immunofluorescent double-labeling experiments the distribution of fibrinogen was compared to that of platelet factor 4 and beta thromboglobulin. All three antigens occurred in virtually all platelets and showed and identical, dotlike distribution. For immunoelectron microscopy we used protein A-colloidal gold on ultra-thin frozen sections to visualize the specific reaction indirectly. The staining for platelet factor 4, beta thromboglobulin, and fibrinogen localized exclusively over alpha-granules of washed platelets. Within the granules, platelet factor 4 was localized preferentially in the electron dense, alpha-granule nucleoid, whereas fibrinogen was more predominant in the electron-lucent granule periphery. Beta thromboglobulin localization did not show a preferential intragranular distribution.

Antigens↗
PubMed1981

[Blood platelet oxygen consumption in pituitary dwarfs (author's transl)].

Oxygen consumption in blood platelets of 14 pituitary dwarfs aged from 2 to 8 years was investigated before and after a 2 months' treatment with growth hormone (GH). No significant difference was found between dwarfs and control subjects in respect of basal platelet oxygen uptake (4.0 +/- 3.8 mmol O2/10(9) platelets/min in dwarfs as against 6.4 +/- 4.1 in controls), but the abrupt increase in oxygen consumption induced by thrombin was significantly reduced in dwarfs (4.3 +/- 4.1) as compared with controls (12.3 +/- 7.6; p less than 0.01). During GH treatment, however, the dwarfs' response to thrombin stimulation was similar to that of controls. Since dwarfs had normal platelet malonyldialdehyde production, it is likely that the mitochondrial component of thrombin-induced high oxygen consumption was deficient. These results suggest that blood platelets may contribute to the protective effect of GH deficiency against atherosclerosis.

Blood Platelets↗
PubMed1985

Immuno-electron microscopical demonstration of lysosomes in human blood platelets and megakaryocytes using anti-cathepsin D.

Immunocytochemistry with affinity-purified anti-human cathepsin D was applied to ultrathin frozen sections of human bone marrow megakaryocytes and of blood platelets from peripheral blood. The fixative used was paraformaldehyde (concentration gradient 2----8%). Protein A/colloidal gold (5 and 8) particles were used as second label. Cathepsin D was localized in primary and secondary lysosomes in blood platelets and in primary and secondary lysosomes in megakaryocytes. Primary lysosomes in megakaryocytes were identified by their localization on the trans-side of the Golgi complex and secondary lysosomes by the presence of inclusions. The lysosomes in platelets differed from alpha-granules by being smaller, lacking an electron dense core, and by the presence of a transparent submembrane halo. Platelets undergoing a release reaction after stimulation with thrombin showed cathepsin-D staining in the surface-connecting tubules.

Blood Platelets↗
PubMed1983

Effect of heavy metals and alkali metals on L-leucine uptake by human blood platelets.

The transport of L-leucine into human blood platelets was characterized as a function of time and amino acid concentration in the medium. Inhibition analyses showed that L-leucine uptake can be only partially inhibited by other amino acids including those which are believed to be transported by the same L system. When Cu2+, Zn2+, Mg2+, Co2+, Fe2+, Ba2+, or Cd2+ were introduced into the transport medium to the final concentrations of 2.5 and 5.0 mM, they inhibited significantly the L-leucine uptake into platelets. In contrast, the initial rate of L-leucine uptake was enhanced by Cu+ ions. Ceruloplasmin, a copper transporting protein, caused almost a complete inhibition of L-leucine uptake.

Adult↗
PubMed1989

Bacterial capacity of blood platelets in patients suffering from pneumonia.

The percent of bacteria engulfed by blood platelets, surviving in them and killed was determined in these cells taken from 22 patients with pneumonia before the treatment and from 14 patients after the treatment. The mean percent of bacteria phagocytosed by platelets collected before the treatment was 6.28 and by those after the treatment 5.01, being considerably higher than in the control group (3.42). The mean percent of bacteria surviving in platelets taken before the treatment equalled 3.10 and after the treatment 2.36 being also higher than in the control group (1.32). The mean percent of bacteria killed by platelets taken before the treatment was 3.18 and by those taken after the treatment 2.65, being also higher than in the control group. These results seem to indicate that in cases of pneumonia the blood platelets are involved into the antibacterial activity.

Blood Bactericidal Activity↗
PubMed1991

Blood platelet count and function are related to total and cardiovascular death in apparently healthy men.

BACKGROUND: Experimental animal and clinical studies indicate that blood platelets have an important role in atherosclerosis and formation of thrombi. Prospective studies presenting evidence of an association between blood platelet count and cardiovascular mortality have not been performed. METHODS AND RESULTS: From 1973 to 1975, blood platelets were counted, and their responsiveness to aggregating agents was studied in healthy middle-aged men. The aim was to assess the possible association between these variables and coronary heart disease. At 13.5 years of follow up, a significantly higher coronary heart disease mortality was observed among the 25% of subjects with the highest platelet counts. Platelet aggregation performed in a random subsample (150 of the 487 men), moreover, revealed that the 50% with the most rapid aggregation response after ADP stimulation had significantly increased coronary heart disease mortality compared with the others. These associations could not be explained by differences in age, lipids, blood pressure, or smoking habits. CONCLUSIONS: The present study is the first to present conclusive, prospective evidence of an association between platelet concentration and aggregability and long-term incidence of fatal coronary heart disease in a population of apparently healthy middle-aged men.

Adenosine Diphosphate↗
PubMed1996

Cisplatin-induced changes in biological activity of blood platelets: thiol-related mechanisms.

The effects of cisplatin (cis-diamminedichloroplatinum (II), CDDP) and transplatin (trans-diamminedichloroplatinum(II), TDDP), and their complexes with glutathione (GS-Pt) in vitro on oxygen free radical generation O2-.), lipid peroxidation and ADP-induced aggregation in pig blood platelets were studied. Incubation of pig blood platelets with cisplatin or transplatin caused a loss of both protein -SH and the thiol groups of GSH. In pig blood platelets exposed to cisplatin or transplatin (20 microM) the GS-Pt complex was formed as a major metabolite. The formation of GS-Pt complexes in platelet cytosol was time dependent and the intracellular content of this complex reached a maximal level after 24 h. GS-Pt complexes were found to induce platelet lipid peroxidation, measured as thiobarbituric acid reactive substance level, and O2-. generation, and it was more active than cisplatin or transplatin alone. Cisplatin and its GS-Pt complex had an inhibitory effect on ADP-induced platelet aggregation. These results showed that GS-Pt complexes affect platelet metabolism and function. It seems that glutathione-associated metabolism of platinum compounds plays an important role in the cytotoxicity and biological activity of these drugs.

Animals↗
PubMed1971

Storage of ATP and 5-hydroxytryptamine in blood platelets of guinea-pigs.

1. By density gradient centrifugation of homogenized blood platelets of guinea-pigs, subcellular organelles have been isolated which exhibit much higher concentrations (mumole/mug protein) of ATP than the whole platelets.2. The organelles also store endogenous 5-HT whose concentration is, however, considerably inferior to that of ATP.3. Investigated by electron microscopy most of the isolated organelles look empty and only very few show dense osmiophilic cores indicating the presence of 5-HT. Accordingly the occurrence of dense osmiophilic organelles in the whole platelets is also very rare.4. Exogenous 5-HT taken up by the platelets markedly accumulates in the subcellular fraction containing the organelles storing ATP. Concomitantly, the platelets show a rise in the number of osmiophilic organelles and the frequency of osmiophilic cores in the isolated organelles is increased.5. From these and previous in vitro experiments it is concluded that the so called 5-HT storage organelles of blood platelets primarily store ATP and only subsequently accumulate 5-HT.

Adenosine Triphosphate↗