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Results for “Platelet activation”

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At least 37 records · Page 2Linked to original sources
PubMed1979

Desensitization of prostaglandin-activated platelet adenylate cyclase.

Prostaglandin D2 (PGD2) is one of several prostaglandins that can inhibit platelet aggregation and activate adenylate cyclase. Platelets were exposed to varying concentrations of PGD2 washed, and the adenylate cyclase response to prostaglandins, epinephrine, and sodium fluoride determined. Incubating platelets with 5 x 10(-5) M PGD2 for 2 hr resulted in a 45% decrease in PGD2 activation of adenylate cyclase and a 25% decrease in stimulation by PGE1. Fluoride activation (7-fold) epinephrine inhibition (30%) and basal enzyme activity were unchanged by exposure of the platelets to PGD2. Desensitization was concentration dependent, with loss of enzyme activity first noted when platelets were incubated with 10(-7) M PGD2. Enzyme sensitivity could be partially restored when desensitized platelets were washed free of PGD2 and incubated in buffer for 2 hr; complete resensitization required incubation for 24 hr in plasma. Regulation of prostaglandin sensitive platelet adenylate cyclase could be of importance in mediating the response of platelets to aggregating agents.

Adenylyl Cyclases↗
PubMed1979

The release of a platelet-activating factor by stimulated rabbit neutrophils.

Normal rabbit peripheral blood neutrophils released a platelet-activating factor upon stimulation by opsonized zymosan. The liberation was Ca++ dependent and the time course of release was closely associated with phagocytosis. The material extracted into chloroform and exhibited an identical mobility by thin layer chromatography to basophil-derived, IgE-stimulated, platelet-activating factor (PAFb). It was similar to PAFb in its effect on platelets in both aggregation and release but was distinguished from ADP, thrombin, arachidonic acid, and thromboxanes. This factor appears to be responsible for some previously reported neutrophil-platelet interactions.

Animals↗
PubMed1979

Biochemical mechanism of platelet activation. Involvement of contractile proteins.

The present state of knowledge of the biochemical mechanism of platelet activation (adhesion, shape change, microspike formation, aggregation, release reaction, clot retraction) is presented under involvement of contractile proteins. The working hypothesis on the contractile mechanism of platelet activation is explained.

Actomyosin↗
PubMed1977

Platelet activation in haemostasis: role of thrombin and other clotting factors in platelet-collagen interaction.

The mechanism of activation of platelets by collagen was examined. Hirudin interfered with the initial collagen-platelet interaction and both hirudin and heparin inhibited collagen-induced release of platelet granular contents. Hirudin completely inhibited the release of both [3H]5HT and beta-glucuronidase whereas heparin completely inhibited release of beta-glucuronidase but only partly inhibited release of [3H] 5HT. beta-Glucuronidase and maximal [3H] 5HT were only released when plasma was present. The results are compatible with an essential intermediary role for thrombin in collagen activation of platelets. Evidence was also obtained that von Willebrand factor may participate in this reaction.

Blood Coagulation Factors↗
PubMed1979

[Semi-synthesis and proposed structure of platelet-activating factor (P.A.F.): PAF-acether an alkyl ether analog of lysophosphatidylcholine].

We have studied the molecular structure of platelet-activating factor" (P.A.F.), a mediator of inflammation obtained from blood leukocytes, macrophages, and platelets themselves. We have semi-synthetized a substance that possesses all the known physicochemical and biological characteristics of P.A.F. from hog leukocytes. This was performed by successive methylation, hydrogenation, and acetylation of lysophosphatidylethanolamine plasmalogen. We therefore propose the following structure for P.A.F.: 1-0-alkyl-2-acetyl-glyceryl-3-phosphorylcholine. This molecular structure is not yet described among the numerous substances capable of inducing platelet aggregation and release.

Acetylation↗
PubMed1977

Platelet activating factor, the trigger of haemostatic alterations in rat anaphylaxis.

Platelet-activating factor (PAF) generated by an IgE-mediated reaction in the peritoneal cabity of rats was partially purified by adsorption to diatomaceous earth. It aggregated rat platelets and, as a consequence, activated Hageman factor in in vitro, as well as in vivo, conditions. The haemostatic alterations induced by PAF showed similarity to those observed in the early phase of rat anaphylaxis.

Anaphylaxis↗
PubMed1979

Modulation of platelet activation by native DNA.

Native DNA (dsDNA) was found to induce the aggregation of isolated human platelets and the release of platelet 5HT; this activation was inhibited by both theophylline and TYA, suggesting a role for cAMP and metabolic products formed from arachidonate. By contrast, nonaggregating amounts of dsDNA inhibited platelet activation induced by collagen or thrombin. This inhibition, which could be overcome by use of greater amounts of the stimulatory agents, was not associated with the loss of platelet viability. Activation of platelets by dsDNA was not observed in plasma or in isolated platelet systems to which small amounts of cell-free plasma were added. However, dsDNA maintained in plasma its ability to inhibit platelet aggregation induced by collagen and thrombin. RNA and single-stranded DNA failed to induce platelet aggregation or release of 5HT and to block the platelet activation stimulated by dsDNA. Further, dsDNA did not significantly inhibit platelet aggregation in platelet-rich plasma stimulated by ADP or epinephrine. These data implicate dsDNA as a selective and potentially important activator and modulator of platelet responsiveness.

Adenosine Diphosphate↗
PubMed1975

IgE-induced release of a platelet-activating factor from rabbit lung.

Sensitized rabbit lung fragments release a platelet-activating factor (PAFL) after challenge with specific antigen or monospecific antibody to rabbit IgE. This release requires calcium and is less evident in lungs from rabbits producing IgG as well as IgE antibody. The PAFL released from lung stimulates the secretion of serotonin from washed rabbit platelets. PAFL is distinguishable from ADP or thrombin and has properties similar to PAF derived from basophils (PAFB). It is not, however, identical to PAFB since rabbit platelets specifically desenitized to PAF still respond by releasing serotonin if stimulated with PAFL.

Animals↗
PubMed1977

Basophil-derived platelet-activating factor (PAF) as an in vivo mediator of acute allergic reactions: demonstration of specific desensitization of platelets to PAF during IgE-induced anaphylaxis in the rabbit.

The anaphylactic response to an i.v. injection of antigen into rabbits making only IgE antibody against the antigen was shown to be preceded by a disappearance of the metachromatic staining properties of the circulating basophils and was accompanied by marked but transient thrombocytopenia. The platelets which returned to the circulation 1 hr after the anaphylaxis were shown to be unresponsive to the secretion-inducing activity of basophil-derived platelet-activating factor (PAF) when compared with platelets examined before antigen challenge. By contrast, platelet responsiveness to other stimuli such as collagen, thrombin, and C3b was unchanged. The specific desensitization to PAF provides strong evidence for the action of this mediator on platelets in vivo during IgE-mediated anaphylaxis and provides a useful tool for detecting the effects of particular cell activators in inflammatory reactions.

Acute Disease↗
PubMed1979

Platelet-activating factor and macrophages. I. Evidence for the release from rat and mouse peritoneal macrophages and not from mastocytes.

Platelet-activating factor (PAF) is a phospholipid mediator of anaphylaxis, released from basophils of several mammalian species, that aggregates platelets and releases their vasoactive amines. The ionophore A23 187 induced the release of PAF from rat and mouse peritoneal cells, a mixed cell population that was fractionated using 5--15% Ficoll gradients and adherence to plastic petri dishes. PAF was associated with large, acid phosphatase-containing, adherent mononuclear cells. Mastocytes did not release PAF but released histamine by the action of ionophore or 48/80; they could not be held responsible for inactivation of PAF or inhibition of the PAF-induced platelet aggregation. These data indicate that, besides blood basophils, peritoneal macrophages are a likely source for PAF, a result that adds a new important function to the macrophage:aggregation of platelets and liberation of their inflammatory and vasoactive substances.

Animals↗
PubMed1977

Platelet activating factor (PAF). A possible direct mediator of anaphylaxis in the rabbit and a trigger for the vascular deposition of circulating immune complexes.

Evidence is presented that IgE-induced, basophil-derived, platelet-activating factor (PAF) causes sequestration of rabbit platelets during sublethal IgE-induced anaphylaxis, and produces a state of specific desensitization in the platelets upon their subsequent return to the circulation. Moreover, depletion of platelets from rabbits undergoing lethal anaphylaxis abrogated the mortality and markedly reduced other parameters of the anaphylaxis. It was suggested that PAF may represent a major mediator of this reaction. A number of lines of evidence have suggested in addition that PAF may play a role in acute experimental immune complex disen that PAF may play a role in acute experimental immune complex disease in rabbits by causing release of vasoactive amines from platelets, lase in rabbits by causing release of vasoactive amines from platelets, leading to increased vascular permeability and deposition of circulating immune complexes along filtering vascular membranes. This data, providing evidence for the action of PAF in vivo and implicating this action in two allergic reactions, supports the contention that PAF is an important mediator of acute allergic reactions.

Anaphylaxis↗
PubMed1979

Comparison of platelet count and platelet protein methods for determination of platelet MAO activity.

Platelet monoamine oxidase (MAO) activity in 10 normal volunteers was studied as a function of platelet protein or electronically-determined platelet counts. Comparisons of the two methods were made for samples assayed on the same day as well as one week later. The MAO activities resulting from both methods were significantly correlated and reproducible but the results of the platelet count method were, in most instances, slightly but significantly more reliable than the platelet protein method. The relevance of these results to the controversy concerning platelet MAO activity in schizophrenia is discussed.

Blood Cell Count↗
PubMed1979

The immunological generation of a platelet-activating factor and a platet-lytic factor in the rat.

Antigen challenge of the rat peritoneal cavity which had been prepared with IgGa-rich antiserum generated activities which released [14C]-serotonin from pre-labelled human platelets. After adsorption of these activities onto Amberlite XAD-8 and elution in 80% ethanol, two factors of differing polarity were resolved by chromatography on diethylaminoethyl cellulose in organic solvents. The activity eluting in the 7:1 chloroform:methanol solvent contained a platelet-lytic factor (PLF) assessed by the parallel release of lactic acid dehydrogenase and [14C]-serotonin; the cytotoxicity of this fraction was confirmed by phase-contrast microscopy examination which demonstrated fragmentation of the exposed platelets. The activity eluting in the 1:1 methanol: aqueous 1.0 M ammonium carbonate solvent was a platelet-activating factor (PAF) as defined by release of [14C]-serotonin without lactic acid dehydrogenase. Both the lytic and the activating principles were separable from slow reacting substance of anaphylaxis and polymorphonuclear leucocyte chemotactic activity, and each presented a single activity peak of differing mobility when chromatographed on silica gel H plates. Human eosinophil phospholipase D inactivated the lytic factor by more than 85% in 2 h at 37 degrees without affecting the activity of the activating factor. The release of [14C]-serotonin induced by the PAF was not affected by the absence of calcium from the medium or by elevations in the platelet concentrations of cyclic AMP or cyclic GMP that resulted from pre-incubation of platelets with prostaglandin D2 or sodium ascorbate, respectively.

Animals↗
PubMed1979

An improvement of the analytical description of temporal variations of plasma and total platelet activities, studied using 75Se-methionin as an in vivo tracer.

In this work we have re-examined our previous model for the analytical description of temporal variations of plasma and total platelet activities, introducing a mathematical simplification by means of elimination of a cumbersome and deforming parameter. We give here 1) interpolation formula 2) complete list of instructions of our program for computer data processing.

Computers↗
PubMed1977

Release of platelet-activating factor and histamine. I. Effect of immune complexes, complement and neutrophils on human and rabbit mastocytes and basophils.

Immune complexes (ICs) triggered the degranulation of basophils/mastocytes in rabbit and man, thus releasing histamine and platelet-activating-factor. ICs acted upon basophils/mastocytes through complement activation and generation of anaphylatoxins and through release of cationic proteins from polymorphonuclear neutrophils. Anaphylatoxins and cationic proteins were active on human and rabbit mastocytes and on human basophils but not on rabbit basophils. Therefore, a cascade of cell to cell interactions may be envisaged implicating successively neutrophils, basophils and/or mastocytes and platelets. These interactions result in enhanced vascular permeability that allows ICs to be trapped along filtering basement membranes. This sequence could perpetuate the deposition of ICs, initially triggered by degranulation of basophils and mastocytes through the IgE-dependent mechanism, and furnish us with an explanation for the rather poorly understood involvement of platelets in immunopathology.

Anaphylatoxins↗
PubMed1979

Chromatographic fractionation and characterization of the active platelet aggregation inhibitory factor from bromelain.

Isolation and characterization of the platelet aggregation inhibitory factor of bromelain have been presented in this study. Commercial bromelain consists of 3 major components as demonstrated by discontinuous sodium chloride gradient chromatography through carbixymethyl-sephadex column. Fraction I constituted approximately 19% of the total fraction. This fraction had no proteolytic activity or platelet aggregation inhibiting activity, but showed peroxidatic activity. Fraction II and III, which constituted the remainder of the fraction eluted with 135 mM and 800 mM NaCl concentrations, respectively, showed both proteolytic and inhibition of platelet aggregation, but no peroxidatic activity. Immunoelectrophoresis and polyacrylamide electrophoresis showed fraction I with beta-mobility while fraction II and III demonstrated gamma-mobility. It is suggested that the proteolytic activity is associated with the inhibition of platelet aggregation, since oxidation of fractions II and III with sodium tetrathionate abolished both activities. The mechanism of inhibition of platelet aggregation by bromelain is presently unknown but may involve its influence on the prostaglandin synthetic pathway of platelets.

Bromelains↗
PubMed1978

Platelet activation: a new biological activity of guinea-pig C3a anaphylatoxin.

3H-serotonin-release from labelled gp-platelets is established as a sensitive method for testing a new biological activity of gp-C3a anaphylatoxin in an autologous situation. Time-, dose- and temperature-dependent release reactions as well as specific inhibition by carboxypeptidase B and anti-C3a antibodies show that C3a is a potent and specific inducer of platelet activation. Inactive C3a does not induce 3H-serotonin-release but specifically inhibits the action of C3a on platelets.

Anaphylatoxins↗