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Biomedical subjects

U Till

Publications and source records attributed to U Till.

At least 91 records · Page 5Linked to original sources
PubMed1984

The influence of PAF on the metabolization of arachidonic acid by human blood platelets.

The cooperative action of PAF and arachidonic acid, collagen or the divalent cation ionophore A 23 187 was studied in human platelet-rich plasma. Besides an augmentation of the platelet aggregation also increased amounts of thromboxane B2 and malondialdehyde are generated. Both effects are inhibited by aspirin indicating that the cyclooxygenase pathway plays a major role in the synergistic platelet activation.

Arachidonic Acid↗
PubMed1984

Dependence of arachidonic acid (AA) metabolization in human blood platelets on reduced coenzymes.

In human platelets the metabolization of AA is linked to a consumption of the reduced coenzymes NADPH and GSH which can be attributed to about 70% to the cyclooxygenase (CO) and to about 30% to the lipoxygenase (LO) pathway. In GSH depleted platelets the conversion of AA in the LO pathway to 12-HETE is strongly impaired, whereas the formation of the stable CO products from exogenous AA is not decreased, but accelerated. When platelets are deprived from GSH by oxidation to GSSG, the release of endogenous AA from phospholipids in activated platelets is inhibited.

Arachidonic Acid↗
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↗
PubMed1984

Halo lipids. VI. Stimulation of human and rabbit blood platelets by racemic halo analogues of O-alkyl-glycerophosphocholine.

Halo analogues of O-alkyl- glycerophosphocholines are shown to stimulate human and rabbit blood platelets. Using 50-500 microM, a concentration dependent platelet aggregation is triggered in human platelet-rich plasma. Distinctly lower concentrations up to 10 microM activate the platelets in rabbit platelet-rich plasma. Moreover, the halo analogues enhance aggregation and release reaction triggered by suboptimal concentrations of ADP. In protein poor mediums the halo lipids in a concentration of 50 microM or higher cause a complete lysis of platelets. These results indicate that the halo lipids tested show the typical behaviour reported on lysophosphatidic acids which has to be taken into account using these compounds for other purposes.

Adenosine Diphosphate↗
PubMed1983

Studies on the stimulation of human blood platelets by semi-synthetic platelet-activating factor.

"Saturated" and "unsaturated" platelet-activating factor (PAF) obtained from ratfish liver oil were proved to exert potent stimulation on human blood platelets. Using 0.025 to 1.0 mumol/1 PAF a dose-dependent platelet aggregation in platelet-rich plasma was observed. During PAF-induced irreversible aggregation a 9 to 40% release of platelet bound serotonin occurred. The specific effect of PAF, however, seems to be limited to induce reversible aggregation since second wave of aggregation and serotonin release were suppressed by a combination of acetylsalicylic acid and an ADP scavenging system. Incubation of PAF for 30 min in plasma resulted in a 90% loss of its platelet aggregating power. Subthreshold concentrations of PAF enhanced the platelet aggregation triggered by suboptimal concentrations of ADP, epinephrine, or collagen. Vice versa non-aggregating concentrations of ADP, epinephrine, collagen, Ca-ionophore A 23,187, or arachidonic acid amplified PAF-induced platelet aggregation. The synergistic effect of PAF and other stimuli of blood platelet activation can be partly interpreted as a stimulating effect of PAF on the metabolization of arachidonic acid.

Adenosine Diphosphate↗
PubMed1983

Diamide mediated deaggregation of activated blood platelets is not caused by changes in adenine nucleotide pattern.

Studies on the effect of diamide (azodicarboxyl-bis-dimethylamide), a glutathione oxidizing agent, on platelet functions revealed an initial acceleration of aggregation followed by a pronounced deaggregation. The whole pattern of adenine nucleotides was followed up during both, arachidonic acid and arachidonic acid + diamide induced aggregation to prove whether the diamide mediated deaggregation is caused by changes in one of the parameters of the energy metabolism, i. e. ATP level, adenylate energy charge or ATP/ADP ratio.

Adenine Nucleotides↗
PubMed1983

Evidence for glutathione-S-transferase activity in human blood platelets.

Data will be presented pointing to the presence of glutathione-S-transferase activity in human blood platelets and the possible involvement of this enzyme in the process of platelet activation. Using 1-chloro-2,4-dinitrobenzene as a synthetic substrate of the glutathione-S-transferase a rapid dose-dependent depletion of platelet glutathione was measured. The formed GSH-CDNB conjugate was separated by thin-layer chromatography. Hints to the formation of leukotriene-like substances by glutathione-S-transferase catalysed reaction were obtained using the specific leukotriene C antagonist FPL 55 712 in aggregation studies.

Arachidonic Acid↗
PubMed1983

Effect of compounds causing reversible perturbation of the cellular thiol-disulfide status on the aggregation of human blood platelets.

Diamide, cumene hydroperoxide, t-butyl hydroperoxide and divicine are compounds which cause a reversible oxidation of cellular SH groups. They influence the aggregation of human platelets in a common manner when added to platelet rich plasma, simultaneously with different types of aggregation inducer: (1) The initial phase of aggregation becomes accelerated. This is accompanied by a more sensitive response to the inducer. (2) The aggregation becomes reversible. The accelerated initial phase of aggregation is followed by a switchover to deaggregation. Addition of diamide to platelet suspensions results in an immediate and fast diminution of the platelet GSH level. Extent and duration of the GSH fall depend on the diamide concentration used. The time courses found for the platelet GSH level suggest a causal connection with the altered aggregation response. Therefore, the conclusion is drawn that perturbation of the cellular thiol-disulfide status influences a fundamental and common part of the platelet activation sequence.

Arachidonic Acid↗
PubMed1983

Differences in morphology and protein pattern of human blood platelets during irreversible and diamide mediated reversible aggregation.

Morphological alterations of platelets during reversible aggregation mediated by diamide are compared with those observed during irreversible aggregation. Diamide prevents cell fusion and the formation of loop-like structures which probably arise from fusing plasma membranes. Differences in the protein pattern of platelets after reversible and irreversible aggregation suggest a specific involvement of SH-proteins in irreversible platelet aggregation. The diamide mediated alterations of platelet aggregation behaviour are transitory, i.e. reversibly aggregated platelets respond normally to a new addition of aggregation inducers without and with diamide, respectively.

Arachidonic Acid↗
PubMed1982

The effect of diamide (azodicarboxylic acid-bis-dimethylamide) on sulfhydryl group content, proteins, and the location of phosphatidylethanolamine in human blood platelets.

Treatment of human blood platelets with the thiol-oxidizing agent, diamide, causes rapid oxidation of glutathione and alterations in aggregation and release reaction. Moreover, cross-linking of proteins was observed. Three high molecular weight bands of 200 - 240 X 10(3) daltons and a band of 66 X 10(3) daltons were involved in this process. After reduction with dithiotreitol the normal pattern was received. In contrast to the erythrocyte, the cross-linking of platelet proteins was not accompanied by a reorientation of phosphatidylethanolamine in the membrane. Also a considerably smaller effect of diamide on platelet protein sulfhydryl group content was measured.

Azo Compounds↗
PubMed1982

Reconsideration of quantitative phospholipid analysis in human gel-filtered blood platelets.

In the literature the values for phospholipid content and the pattern of human gel-filtered platelets diverge considerably. In order to find the possible reasons for these discrepancies, the separation of plasma constituents from gel-filtered platelets and the influence of different extraction methods were reinvestigated. The critical point in phospholipid determination of platelets appeared to be the completeness of plasma lipid separation from platelets and not the extraction method. Avoiding contamination by plasma lipids the results with gel-filtered platelets correlated to that obtained with washed platelets.

Blood Platelets↗