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Biomedical subjects

J F Mustard

Publications and source records attributed to J F Mustard.

At least 127 records · Page 7Linked to original sources
PubMed1980

Heparin inhibits thrombin binding to rabbit thoracic aorta endothelium.

Thrombin binding to freshly prepared sections of rabbit thoracic aorta was studied. After the sections had been exposed to a range of concentrations (0.1 to 3.8 IU/ml) of 125I-labeled thrombin for various periods of time at 37 degrees C, endothelial Häutchen preparations were obtained, and their radioactivity content was determined. Scatchard plot analysis of the data indicated that approximately 5.8 X 10(5) molecules of thrombin associated with each endothelial cell, with a KD of 2.6 X 10(08)M. By incubation with an excess of unlabeled thrombin, 50% of bound 125I-labeled thrombin was displaced from the endothelium in 7.3 min. Exposure of the endothelial surface to heparin (1 to 10 USP U/ml) did not significantly affect subsequent thrombin binding. However, incubation of the aorta in a thrombin solution containing 1 to 10 USP U/ml heparin did reduce enzyme binding to the endothelium by up to 60%. Similarly, the presence of heparin inhibited thrombin binding to the thoracic aorta of exsanguinated rabbits in situ. Endothelium, to which 125I-labeled thrombin was bound, lost 50% to 70% of the bound enzyme when suspended in a solution containing heparin (10 USP U/ml) and compared to the control incubated without heparin. These observations are consistent with the proposal that a major portion of endothelium-bound thrombin may be associated with pericellular heparan sulfate; heparin competes for thrombin with the heparan sulfate sites, and because of its higher affinity for thrombin, heparin displaces bound thrombin from, or inhibits binding of free thrombin by, the endothelium.

Animals↗
PubMed1980

Platelet sialic acid and platelet survival after aggregation by ADP.

Some investigators have reported recently that platelet surface sialic acid is decreased during ADP-induced aggregation, whereas others have reported an increase. Since removal of sialic acid from the platelet surface shortens platelet survival, we have determined the survival of platelets that have been aggregatad by ADP. We have also measured the amount of sialic acid in the suspending fluid of platelets after ADP-induced aggregation. ADP-induced aggregation did not cause the loss of sialic acid from rabbit platelets (which do not undergo a release reaction in response to ADP) nor from washed human platelets in a medium containing physiologic concentrations of calcium in which granule contents are not released. In a medium without added calcium, ADP caused the release of 14C-serotonin (42.5% +/- 3%) from human platelets, but less than 4% of the sialic-acid-containing material was released. It seems likely that little of the releasable sialic acid of platelets is in the dense granules or the alpha-granules. Thrombin (5 U/ml) released 90.0% +/- 3.4% of the serotonin from human platelets but only 20.6% +/- 7.4% of the total sialic-acid-containing material. Neuraminidase removed 42.3% of the total sialic acid, presumably from the platelet surface. Rabbit platelets that had been aggregated by ADP and deaggregated survived normally when returned to the circulation. This observation also provides evidence that they had not lost membrane sialic acid during aggregation and deaggregation.

Adenosine Diphosphate↗
PubMed1979

Shortening of the bleeding time in thrombocytopenic rabbits after exposure of jugular vein to high aspirin concentration.

Aspirin, in doses which inhibit platelet thromboxane A2 production, prolongs the bleeding time but this effect on the bleeding time is lost when doses of aspirin which also inhibit vessel wall prostaglandin I2 (PGI2) production are used. PGI2 is both a potent inhibitor of platelet aggregation and a powerful vasodilator. We have investigated the contribution of the vascular effect of PGI2 on hemostasis by studying the effect of high concentrations of aspirin on the jugular vein bleeding time in severely thrombocytopenic rabbits and on the loss of non-platelet-containing fluid from standard puncture wounds in aspirin-treated veins perfused under constant pressure. After aspirin treatment, the bleeding time was significantly shortened in both normal and thrombocytopenic rabbits. This effect was associated with a decreased production of PGI2-like material by the vessel wall and a reduction in the volume of fluid lost from the standard puncture wound in the jugular vein. The effect of aspirin on the bleeding time and on PGI2 production was relatively short-lived and the bleeding time returned to normal within 2-3 hours. These observations indicate that PGI2 can influence hemostasis by mechanisms independent of platelet aggregation.

Animals↗
PubMed1979

The influence of red blood cells on the effects of aspirin or sulphinpyrazone on platelet adherence to damaged rabbit aorta.

The effects of acetylsalicylic acid (ASA; aspirin) or sulphinpyrazone (SP) on the adherence of washed rabbit platelets to the subendotheilial surface of an everted aorta mounted on a probe or to the subendothelial surface of a rabbit aorta attached to a perfusion apparatus were examined. ASA had no effect on platelet adherence to a damaged aorta perfused with a suspension of washed platelets in a medium containing 10% red blood cells (RBC); SP was slightly inhibitory at high concentration. When damaged rabbit aortae were everted on a probe and rotated in a suspension of washed platelets to which RBC were added to a packed cell volume of 10%, both ASA and SP inhibited platelet adherence to the damaged vessel wall. When the PCV was 40%, ASA was not inhibitory and SP reduced platelet adherence only at very high concentrations. It is therefore unlikely that, at the concentrations achieved in man, SP exerts an effect on platelet adherence. The different effects of ASA and SP on platelet survival do not appear attributable to their effects on platelet adherence.

Animals↗
PubMed1979

Platelet interactions with the endothelium and the subendothelium: the role of thrombin and prostacyclin.

The adherence of 51Cr-labeled platelets to rabbit aortae everted on probes rotated in platelet-red cell suspensions has been measured. Platelet adherence to the subendothelium exposed by passage of a balloon catheter before everting the aortae was inhibited by compounds that increase platelet cyclic AMP levels (PGE1, PGI2 or dipyridamole). These agents, however, did not abolish platelet adherence to the subendothelium. Aspirin treatment of the vessel wall was used to block PGI2 production; platelet adherence to the surface of the 'undamaged' aorta and the subendothelium was studied following this treatment. Since aspirin treatment of the 'undamaged' vessel wall did not cause platelets to adhere to it, it seems unlikely that PGI2 formation by the vessel wall is the mechanism that prevents platelet adherence to normal endothelium. In addition, PGI2 formation by the vessel wall does not appear to influence platelet adherence to the subendothelium, since adherence was not increased by aspirin treatment of the damaged wall. Thrombin treatment of the 'undamaged' vessel wall increased platelet adherence to the surface, but the adherent platelets were seen to be adherent only to small areas where the endothelium was lost or damaged. Heparin reversed the effect of thrombin. Similar results were found when the subendothelium was exposed to thrombin or thrombin and heparin.

Animals↗
PubMed1979

Shortening of the bleeding time in rabbits by hydrocortisone caused by inhibition of prostacyclin generation by the vessel wall.

The effect of hydrocortisone on thrombocytopenic bleeding has been studied in rabbits using a jugular vein bleeding-time technique and a microvascular bleeding-time technique. An inverse relationship was found between the bleeding time and platelet count with both techniques in rabbits made thrombocytopenic by either X-irradiation or injection of heterologous platelet antiserum. Hydrocortisone shortened both bleeding times in thrombocytopenic animals when given in single large doses intravenously (25-100 mg/kg), in daily doses (6 mg/kg) intramuscularly, and shortened the jugular bleeding time when applied to the outside of the jugular vein or instilled intraluminally into the vein. This effect was also noted in normal animals. The effect on thrombocytopenic bleeding was dose related. When given daily, the effect was greater when hydrocortisone was given for 10 d than for 5 d. Both indomethacin and tranylcypromine also reduced the jugular vein bleeding time when instilled intraluminally into the jugular vein, whereas exogenously provided arachidonic acid reversed the effect of hydrocortisone but did not reverse the effect of indomethacin or tranylcypromine. Exogenously provided linoleic acid did not have any effect. Perfusion of the vessel segment with prostacyclin (PGI(2)) reversed the effect of intraluminally administered hydrocortisone, indomethacin, and tranylcypromine. Similarly, hydrocortisone, indomethacin, and tranylcypromine all reduced the rate of loss of fluid from a standard wound in isolated vessels emptied of blood and perfused with saline under constant pressure. PGI(2) reversed the action of these three agents, however, arachidonic acid reversed only the effect of hydrocortisone and did not reverse the effect of indomethacin and tranylcypromine. The generation of PGI(2)-like material and 6-keto-prostaglandinF(1) alpha from jugular vein strips was prevented by prior exposure of the animals or vessel wall to hydrocortisone. These results are compatible with the hypothesis that the vessel wall releases smooth muscle-relaxing prostaglandins when injured and that inhibition of prostaglandin formation by hydrocortisone enhances hemostasis by allowing vasoconstriction to be maintained.

Animals↗
PubMed1979

Platelet interaction with damaged rabbit aorta.

We have quantified the accumulation of 51Cr-labeled washed rabbit platelets on the subendothelium of rabbit aortae following injury with a balloon catheter. The amount of radioactivity that became associated with the damaged wall within 10 minutes of the injury did not change appreciably during the following 24 hours, indicating that there was little turnover of platelets on the injured vessel wall. In addition, by injecting 51Cr-labeled platelets into rabbits at different times after injury, it was possible to estimate the reactivity of the exposed surface to newly injected platelets. Scanning electron microscopy showed that a monolayer of platelets initially formed on the injured surface; the number of platelets associated with the surface decreased over the 7-day observation period. The amount of 51Cr associated with the injured vessel wall also diminished during this period. The ability of the damaged surface to attract fresh platelets gradually decreased during the 7 days following injury. Platelet survival in rabbits was not significantly reduced following the removal of the aortic endothelium (balloon catheter injury 66.3 +/- 12.2 hours, sham operated 72.1 +/- 7.2 hours, untreated controls 76.2 +/- 3.8 hours). Thus, in rabbits, it cannot be assumed that platelet survival provides an estimate of endothelial injury in all circumstances.

Animals↗