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Biomedical subjects

J F Mustard

Publications and source records attributed to J F Mustard.

At least 109 records · Page 6Linked to original sources
PubMed1982

Effect of dipyridamole and prostacyclin on rabbit platelet adherence in vitro and in vivo.

The adherence of 51Cr-labeled platelets to the subendothelium of rabbit aortas was inhibited in vitro and in vivo by high concentrations of dipyridamole (100 microM in vitro, 2.5 or 12.5 mg/kg in vivo). Dipyridamole (100 microM) inhibited release of 14C-serotonin from platelets that adhered to the subendothelium or to a collagen-coated glass surface; lower concentrations of dipyridamole had only a slight inhibitory effect. Scanning electron microscopy showed that many of the platelets that adhered to the subendothelium were rounded, with few pseudopodia. The combination of dipyridamole with PGI2 was no more inhibitory of platelet adherence than either agent alone; however, this combination of inhibitors exerted synergistic inhibitory effects on aggregation and release of 14C-serotonin from platelets aggregated by collagen. The effects of dipyridamole on platelet adherence are a consequence of the action of dipyridamole alone and do not appear to result from its interaction with PGI2 formed by injured vessels in vivo, since the inhibitory effect is not influenced by aspirin inhibition of PGI2 formation, either at the shear rates in the in vitro studies or under the shear conditions found in rabbit aortas in vivo.

Animals↗
PubMed1982

The use of the synthetic peptide, Gly-Pro-Arg-Pro, in the preparation of thrombin-degranulated rabbit platelets.

The method for preparing thrombin-degranulated platelets has been modified to avoid the use of plasmin or successive treatments with small amounts of thrombin, while still achieving more than 90% release of platelet amine storage granule contents. It was necessary to prevent the fibrinogen released from the platelets during thrombin treatment from forming an insoluble fibrin mesh that could trap the platelets and hinder their deaggregation. To accomplish this we have treated rabbit platelets with 0.73 U/ml of thrombin for 1 min in the presence of the synthetic peptide, Gly-Pro-Arg-Pro, which prevents the polymerization of fibrin molecules. We have demonstrated that it also prevents 125I, initially added as 125I-fibrinogen, from associating with the platelets in a form that was not removed by centrifuging and washing during the preparation of thrombin-degranulated platelets, and we infer that products formed from the fibrinogen released from the platelets would also be prevented from associating with them. Thrombin-degranulated platelets prepared by this method have lost 92% of their granule contents and they can be washed and resuspended. These platelets aggregate normally upon stimulation with thrombin, adenosine diphosphate (ADP), or arachidonate. Thus, Gly-Pro-Arg-Pro is useful in preparing thrombin-degranulated platelets for studying platelet reactions without the complicating effects of released materials such a ADP and fibrinogen.

Animals↗
PubMed1982

Thrombin generation and fibrin formation following injury to rabbit neointima. Studies of vessel wall reactivity and platelet survival.

Using platelets prelabeled with 51Cr, we have quantified the effect of injury to the neointima on platelet accumulation, thrombus formation at different times following injury, and the effect of injury to the neointima on platelet survival. Platelet accumulation on the neointima is largely determined by activation of coagulation and thrombus formation; this contrasts with platelet accumulation on the subendothelium where coagulation does not play a major role and where few thrombi form. Heparin treatment significantly inhibits platelet accumulation on the injured neointima but is without effect on platelet accumulation on the subendothelium. Like the subendothelium, the neointima rapidly becomes nonreactive to further platelet accumulation, and the platelets and platelet-fibrin thrombi are lost from the surface in the first few days after injury. Despite the formation of extensive platelet thrombi on the injured neointima, platelet survival is unaffected.

Animals↗
PubMed1982

An investigation into the role of coagulation factor XIII in ADP-induced aggregation and fibrinogen binding with rabbit platelets.

Because there was a possibility that activated factor XIII (factor XIIIa) might stabilize a platelet-fibrinogen aggregate through its crosslinking action, we have isolated plasma factor XIII, activated it, and studied the effect of factor XIIIa at a concentration of 3.3 micrograms/ml on aggregation and 125I-fibrinogen binding of rabbit platelets stimulated with 9 microM ADP. Factor XIIIa did not cause aggregation in the absence of ADP, nor did it enhance ADP-induced aggregation or substantially stabilize the platelet aggregate. The presence of factor XIIIa did not affect the amount of fibrinogen bound to platelets immediately after stimulation with ADP, but it appeared to cause a slow specific binding of 125I-fibrinogen to platelets whether or not they were stimulated with ADP. This binding, which was not inhibited by prostaglandin E1, did not lead to aggregation and was accompanied by crosslinking of fibrinogen through its A alpha and gamma chains, either to other fibrinogen molecules or to a platelet protein or proteins.

Adenosine Diphosphate↗
PubMed1982

Changes in phosphatidylinositol-4,5-bisphosphate 10 seconds after stimulation of washed rabbit platelets with ADP.

Adenosine diphosphate (ADP) induced aggregation of rabbit platelets, without the release reaction, causes a significant decrease (7%) in the amount of phosphatidylinositol-4,5-bisphosphate (PIP2) at 10 sec and at 60 sec (11%). In platelets prelabeled with 32P-phosphate, this decrease in PIP2 is associated with a decrease in PIP2 radioactivity, which is significant at 50 sec. The decrease in PIP2 is sufficient to mobilize about 0.18 nmole Ca2+/10(9) platelets. In view of the key role played by Ca2+ in ADP-induced platelet shape change and aggregation, this evidence is compatible with the hypothesis that changes in PIP2 can be a source of calcium for cellular responses to agonists.

Adenosine Diphosphate↗
PubMed1981

The effect of phospholipase inhibitor mepacrine on platelet aggregation, the platelet release reaction and fibrinogen binding to the platelet surface.

We have examined whether inhibition by mepacrine or freeing of arachidonic acid from platelet phospholipids inhibits platelet aggregation to collagen, thrombin or ADP, and the release reaction induced by thrombin or collagen. Loss of arachidonic acid was monitored by measuring the amount of 14C feed from platelets prelabelled with 14C-arachidonic acid. Mepacrine inhibited 14C loss by more than 80% but did not inhibit thrombin-induced platelet aggregation and had a small effect on release. ADP-induced platelet aggregation did not cause 14C loss. Mepacrine inhibited ADP-induced platelet aggregation by inhibiting the association of fibrinogen with platelets during aggregation. The effect of mepacrine on fibrinogen binding could be considerably decreased by washing the platelets but the inhibition of 14C loss persisted. Platelets pretreated with mepacrine and then washed show restoration of aggregation to collagen. Thus, mepacrine has two effects; 1. it inhibits phospholipases, 2. it inhibits fibrinogen binding. Freeing of arachidonic acid is not necessary for platelet aggregation or the release reaction.

Adenosine Diphosphate↗
PubMed1981

Enhanced platelet accumulation onto injured carotid arteries in rabbits after aspirin treatment.

Prostacyclin (PGI2) is a powerful inhibitor of platelet aggregation, but its role in the pathogenesis of arterial thrombosis is uncertain. We have studied the thrombogenic effect of inhibiting PGI2 production by aspirin (ASA) in carotid arteries of rabbits given 0, 3, 10, or 100 mg ASA/kg either 1, 3, 6, or 20 h beforehand. Platelet accumulation onto injured carotid arteries was enhanced with ASA in a dose of 10 mg/kg. A higher dose of ASA (100 mg/kg) had no further effect. The enhanced thrombogenic effect of ASA persisted for at least 20 h and was associated with a decrease in vessel wall PGI2 production. There was a strong inverse correlation (r = 0.55, P less than 0.01) between PGI2 production and platelet accumulation. The findings suggest that the margin of safety in obtaining an antithrombotic effect of ASA and producing a potential thrombotic effect in arteries may not be as large as predicted by studies using cultured endothelial cells or experimentally induced thrombosis in veins.

Animals↗
PubMed1981

Inhibitors of ADP-induced platelet aggregation prevent fibrinogen binding to rabbit platelets and cause rapid deaggregation and dissociation of bound fibrinogen.

125I-fibrinogen binds to washed rabbit platelets when they ar stimulated wit ADP, and it has previously been observed that fibrinogen binding is prevented by several inhibitors of ADP-induced aggregation. We have now shown that other inhibitors of aggregation, the phosphodiesterase inhibitors caffeine and dipyridamole, and colchicine and cytochalasin B which affect the platelet cytoskeleton, also inhibit specific 125I-fibrinogen binding. A positive correlation was observed between ADP-induced aggregation and fibrinogen binding at limiting concentrations of these inhibitors. Colchicine and cytochalasin B appear to act independently, with no indication of synergism. When any of these inhibitors, as well as those previously tested (EDTA, EGTA, PGE1 and PGI2) was added to platelets that had already been stimulated with ADP and undergone considerable aggregation and fibrinogen binding, it caused rapid deaggregation of the platelets and dissociation of bound fibrinogen, although in some cases the inhibitory effects were not as pronounced as when the inhibitor was added before ADP stimulation. These observations reinforce the concept that fibrinogen plays an essential role in the formation of ADP-induced platelet aggregates.

Adenosine Diphosphate↗
PubMed1980

Prostaglandins and platelets.

Release of arachidonate from cell membrane phospholipids by activation of phospholipase A1 is a key step in the formation of prostaglandins and thromboxanes. In platelets PGH2 and TXA2 are formed from arachidonate and can cause aggregation and the release of granule contents; in vascular tissue, PGI2 is formed instead and, by increasing platelet cAMP, inhibits platelet reactions. There is considerable interest in inhibitors of the enzymes in these pathways as drugs to modify thrombus formation. Results of the clinical trials, however, indicate that drugs which inhibit cyclo-oxygenase may not have a major effect on the thromboembolic complications of arterial disease.

Arachidonic Acids↗