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Biomedical subjects

J F Mustard

Publications and source records attributed to J F Mustard.

At least 181 records · Page 10Linked to original sources
PubMed1976

Sodium arachidonate can induce platelet shape change and aggregation which are independent of the release reaction.

Sodium arachidonate causes shape change and aggregation of rabbit or human platelets that have been washed and then degranulated by treatment with thrombin. Since these platelets do not contain releasable adenosine diphosphate (ADP) and the aggregation is not inhibited by the creatine phosphate-creatine phosphokinase system, sodium arachidonate must be able to cause aggregation that is independent of the release of ADP. Since aggregation of these platelets induced by sodium arachidonate is inhibited by acetylsalicylic acid or indomethacin, it seems likely that products (such as prostaglandin G2) formed from sodium arachidonate are responsible for aggregation. Thus, sodium arachidonate-induced shape change and aggregation of platelets may be caused (i) by the release of ADP by products of sodium arachidonate metabolism and (ii) directly by the products of sodium arachidonate metabolism, independently of released ADP.

Adenosine Diphosphate↗
PubMed1976

In vitro and in vivo functions of thrombin-treated platelets.

Thrombin-induced platelet aggregation has been generally believed to be irreversible. However, thrombin-induced aggregation of washed platelets is reversible if fibrin formation is prevented or the fibrin which binds the platelets together is removed from the platelet aggregates. After treatment with high concentrations of thrombin (0.5 units/ml) single platelets can be recovered that have lost practically all of their releasable serotonin and adenine nucleotides. These platelets are able to aggregate upon addition of low concentrations of ADP in the presence of fibrinogen. They aggregate in response to the ionophore A23, 187 in the absence of added fibrinogen, whereas sodium arachidonate-induced aggregation requires added fibrinogen. Thrombin-treated platelets change their shape in response to collagen in the absence of fibrinogen, and will aggregate upon the addition of collagen providing fibrinogen is present. This response to collagen can be blocked with aspirin but not with a mixture of creatine phosphate/creatine phosphokinase. Upon a second exposure to thrombin, thrombin-pretreated platelets do not change their shape and do not undergo aggregation. Thrombin-pretreated platelets will not retract a thrombin-induced fibrin clot unless ADP, sodium arachidonate, the ionophore A23, 187 or collagen are added together with thrombin. The ability of thrombin-treated platelets to adhere to the exposed subendothelial surface of the rabbit aorta is reduced, compared with untreated control platelets. The thrombin-treated platelets shorten the bleeding time of thrombocytopenic rabbits. However, the are not as effective in shortening the bleeding time as normal control platelets. When injected into rabbits with a normal platelet count, the thrombin-treated platelets that circulate after infusion survive for the same length of time as untreated control platelets. These findings indicate that thrombin-induced platelet aggregation with extensive release of granule constituents is not irreversible and that thrombin treatment does not cause irreversible damage of all platelets that would lead to their immediate elimination from the circulation. Furthermore, these platelets can still be haemostatically effective. It is conceivable that platelets that have lost their amine storage granule contents during a release reaction in vivo, such as may occur in certain cases of intravascular coagulation and repeated episodes of thrombosis, may be found in the circulation of man.

Adenosine Diphosphate↗
PubMed1976

Clq inhibition of the interaction of collagen with human platelets.

Human Clq, isolated in pure state after affinity chromatography on IgG-Sepharose, inhibited collagen-induced aggregation and release of 14C-Serotonin from prelabeled human platelets. Platelet aggregation induced by ADP or thrombin was not inhibited by Clq. Also, the adherence of platelets to glass surfaces was significantly diminished by Clq. In contrast, aggregated Clq mimicked the effect of collagen in causing platelet aggregation and release of serotonin. It appears that monomeric Clq, which has structural similarities to collagen competes with collagen for specific sites on the platelet surface.

Adenosine Diphosphate↗
PubMed1976

Platelet antiplasmin: its extrusion during the release reaction, subcellular localization, characterization, and relationship to antiheparin in pig platelets.

Antiplasmin activity was shown to be released from washed pig platelets by thrombin following a time course similar to that of 3H-serotonin. Antiheparin activity (platelet factor 4) appeared to be released by thrombin at a slower rate than 3H-serotonin or antiplasmin activity. Subcellular fractionation of pig platelets showed that the storage site for antiplasmin is probably the dense (amine storage) granules. Antiheparin was distributed among all of the subcellular particulate fractions except the fraction rich in dense granules. Material released from washed pig platelets and concentrated by ZnSO4 precipitation (crude antiheparin) was found to be rich in antiplasmin activity. Gel filtration on Sephadex G-150, DEAE cellulose column chromatography, and polyacrylamide gel electrophoresis showed that pig platelet antiplasmin is a low molecular weight (approximately 30,000 d) material of alpha1-globulin electrophoretic mobility. It was found to be heat labile and also inhibitory to the caseinolytic activity of trypsin but had no effect on the action of thrombin on fibrinogen. These data indicate that platelet antiplasmin is distinct from platelet antiheparin.

Animals↗
PubMed1976

Effects of sodium periodate on platelet functions.

Removal of N-acetylneuraminic acid from the platelet surface causes rapid removal of platelets from the circulation but causes little change in other platelet functions. We have now investigated the effects of sodium periodate which is thought to oxidize the sialic acid of glycoproteins on cell surfaces and has been shown to affect the functions of other cells. NaIO4 (1 to 10 mm) caused aggregation of stirred suspensions of washed platelets from rabbits. Calcium was required in the suspending medium for NaIO4-induced aggregation. Aggregation was not accompanied by the release of amine storage granule contents nor by cell lysis. Aggregation induced by NaIO4 was not inhibited by creatine phosphate-creatine phosphokinase, by platelet inhibitors that raise platelet cyclic AMP levels such as prostaglandin E1 or methylxanthines, by agents that modify platelet surface--SH groups (N-ethylmaleimide, p-chloromercuribenzene sulfonate), nor by cytochalasin B and/or colchicine which interfere with platelet contractile processes. Drugs such as acetylsalicyclic acid, penicillin G, or cephalothin had no effect on NaIO4-induced aggregation. NaIO4-induced aggregation was practically independent of platelet metabolism since it was not affected by low temperatures and was only slightly inhibited by a combination of antimycin and iodoacetate. Periodate treatment enhanced CO2 production by platelets. When rabbit platelets were pretreated, without stirring, with NaIO4 (0.01 to 1 mm), they did not aggregate. They retained their disc shape and granule contents. However, this pretreatment with NaIO4 inhibited aggregation induced by ADP and inhibited both aggregation and release induced by collagen, thrombin, arachidonic acid, and the ionophore A23,187. The extent of inhibition corresponded to the concentration of NaIO4 used to pretreat the platelets. In contrast, concanavalin A-induced aggregation was unchanged by NaIO4 pretreatment. When NaIO4 oxidation was followed by sodium borohydride (NaBH4) reduction, the effects caused by NaIO4 pretreatment on ADP-induced aggregation and collagen- or thrombin-induced aggregation and release were partially reversed. Pretreatment with NaIO4 also diminished the rate of serotonin uptake and decreased the ability of platelets to adhere to collagen-coated surfaces or to the subendothelial structures of the rabbit aorta. Platelets which had been treated with NaIO4 and then reinfused into rabbits did not survive, and in this way were similar to platelets from which surface sialic acid had been removed by neuraminidase treatment. Since NaIO4 has been shown to oxidize sialic acid on red cell membranes, it seems probably that alteration of surface sialic acid resulted in recognition of the periodate-treated platelets as "foreign" by the reticuloendothelial system. When NaIO4 oxidation was followed by NaBH4 reduction, platelet survival returned toward normal values.

Adenosine Diphosphate↗
PubMed1976

The Gordon Wilson lecture: function of blood platelets and their role in thrombosis.

The role of platelets in thrombosis has been reviewed. The possible relationship between platelets and thrombosis, vessel injury and the development of atherosclerosis is discussed. The implications of our understanding of platelets in thrombosis and clinical complications of arterial disease is reviewed together with possible value if drugs which modify platelet function.

Arteriosclerosis↗
PubMed1976

Loss of sulfated proteoglycan from the surface of rabbit platelets during adenosine 5'-diphosphate-induced aggregation.

Rabbit platelets were labeled in vivo by intravenous injection of 35SO4=60 hours before the animals were exsanguinated. The labeled platelets were washed and resuspended in Tyrode's solution containing 0.35 per cent albumin. The aggregated normally upon the addition of ADP and during aggregation 14.0 +/- 2.7 per cent (mean +/- standard deviation) of the labeled material was lost into the suspending medium. The extent of loss was dependent on ADP concentration and was inhibited by inhibitors of ADP-induced aggregation (AMP, ATP, adenosine, prostaglandin E1, parachloromercuribenzensulfonate and lack of calcium). Since neither release of granule contents nor lysis occurs when rabbit platelets are aggregated by ADP, it was concluded that the labeled material that was lost had been part of the surface coat of the platelets. The labeled material has been identified in other studies as a proteoglycan in which the mucopolysaccharide is principally chondroitin sulfate A. Loss of this material did not make the platelets unresponsive to ADP. The platelets did not reincorporate labeled proteoglycan from plasma. Thrombin caused the release of 50 to 80 per cent of the total platelet-labeled material, presumably from both the granules and the surface. The functional significance of the loss of surface proteoglycan during platelet aggregation is unknown.

Adenosine Diphosphate↗
PubMed1975

The role of blood and platelets in atherosclerosis and the complications of atherosclerosis.

There appear to be at least three ways in which the blood, and particularly the platelets, may contribute to the development of atherosclerosis and its complications: 1. In the mechanism causing endothelial injury and the response of the smooth muscle cells to vessel injury. 2. Through the formation of persistent mural thrombi which are organized into intimal thickenings. 3. Through the formation of thrombi in association with advanced atherosclerosis that may be either (a) mural thrombi which fragment and shower the distal circulation with platelet emboli or (b) occlusive thrombi.

Arteriosclerosis↗
PubMed1975

Transport and storage of serotonin by thrombin-treated platelets.

Repeated thrombin treatment of washed platelets prepared from rabbits can decrease the serotonin content of the platelets by about 80%. When these platelets are deaggregated they reaccumulate serotonin but their storage capacity for serotonin is reduced by about 60%. If thrombin-pretreated platelets are allowed to equilibrate with a high concentration of serotonin (123 mu M), they release a smaller percentage of their total serotonin upon further thrombin treatment, in comparison with the percentage of serotonin released from control platelets equilibrated with the same concentration of serotonin calculations indicate that in thrombin-treated platelets reequilibrated with serotonin, two-thirds of the serotonin is in the granule compartment and one-third is in the extragranular compartment, presumably the cytoplasm. Analysis of the exchange of serotonin between the suspending fluid and the platelets showed that thrombin treatment does not alter the transport rate of serotonin across the platelet membrane and does not cause increased diffusion of serotonin from the platelets into the suspending fluid. The primary reason for the reduced serotonin accumulation by the thrombin-treated platelets appears to be loss of amine storage granules or of the storage capacity within the granules.

Animals↗
PubMed1975

Transfer of adenine nucleotides between the releasable and nonreleasable compartments of rabbit blood platelets.

The metabolic pool of adenine nucleotides in platelets can be labeled by incubating platelets for 1 h in vitro with [14C]adenosine or [32P]orthophosphate. When these platelets are treated with thrombin, the adenine nucleotides released are not labeled. Because of this, Holmsen's suggestion of a metabolically inert pool of granule nucleotides has been generally accepted. We have found that upon incubation of labeled rabbit platelets for longer times (up to 6 h) in vitro, or upon reinjection and reharvesting at times up to 66 h, the releasable pool of adenine nucleotides becomes labeled. Because the rates of 32p and 14C incorporation into this releasable pool are similar, it seems likely that these labels enter the granules as ATP. Equilibrium between the metabolic and granule pools is complete by 18 h. When rabbit platelets are labeled in vivo by intravenous injection of [32P]orthophosphate, peak labeling occurs between 60 and 70 h; this corresponds to their maturation time. The platelets probably incorporate 32P during their production in the megakaryocytes. The specific radioactivity of the adenine nucleotides in the releasable (granule) pool of these platelets is the same as the specific radioactivity in the nonreleasable (metabolic) pool. Since inorganic phosphate in platelets (and undoubtedly in the megakaryocytes) exchanges with inorganic phosphate in plasma, and since the radioactivity of the latter decreases rapidly, the adenine nucleotides in the two pools must exchange to maintain the same specific radioactivity. Transfer of adenine nucleotides into storage granules may represent a general phenomenon because it has been observed in the chromaffin cells of the adrenal medulla also.

Adenine Nucleotides↗
PubMed1975

Factors responsible for ADP-induced release reaction of human platelets.

Extensive aggregation of human platelets can be induced by ADP without secondaryaggregation or release of granule contents. This occurs with washed platelets in Tyrode solution containing 0.35% albumin, human fibrinogen, and apyrase, and in platelet-rich, heparin- or hirudin-plasma. Conditions that caused release during ADP-inducedaggregation were-citrate as the anticoagulant in platelet-rich plasma; addition of citrate (11-15 mM) to a suspension of washed platelets, or to hirudin-plasma or heparin-plasma; suspension of platelets in a medium containing magnesium but no calcium;and the presence of trace amounts of thrombin or aggregated gamma globulin in the platelet suspensions. Acetylsalicylic acid, phenylbutazone, or sulfinpyrazone inhibited secondary aggregation and release in all these circumstances. Heparin or hirudin inhibited ADP-INDUCED SECONDARY AGGREGATION AND RELEASE PROMOTED BY TRACES OF THROMBIN. Although fibrinogen is required for ADP-induced primary aggregation, it does not support secondary aggregation and release, provided that it has no clot-promoting activity. The main agent responsible for ADP-induced secondary aggregation and release in human, citrated, platelet-rich plasma appears to be sodium citrate. Suspending washed human platelets in a medium without calcium mimics the effect of citrate.

Adenosine Diphosphate↗