Metabolic and kinetic study of thrombogenesis: Regulatory mechanism in early step of platelet plug formation

SummaryIn 7 healthy volunteers, formation of thrombin (represented by fibrinopeptide A (FPA) generation, α-granule release (represented by β-thromboglobulin [βTG] release) and the generation of thromboxane B2 (TxB2) were measured in vivo in blood emerging from a template bleeding time incision. At the site of plug formation, considerable platelet activation and thrombin generation were seen within the first minute, as indicated by a 110-fold, 50-fold and 30-fold increase of FPA, TxB2 and PTG over the corresponding plasma values. After a further increase of the markers in the subsequent 3 minutes, they reached a plateau during the fourth and fifth minute. A low-dose aspirin regimen (0.42 mg.kg-1.day-1 for 7 days) caused >90% inhibition of TxB2formation in both bleeding time blood and clotted blood. At the site of plug formation, a-granule release was substantially reduced within the first three minutes and thrombin generation was similarly inhibited. We conclude that (a) marked platelet activation and considerable thrombin generation occur in the early stages.of haemostasis, (b) α-granule release in vivo is partially dependent upon cyclo-oxygenase-controlled mechanisms and (c) thrombin generation at the site of plug formation is promoted by the activation of platelets.

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Haemostatic Platelet Plug Formation in the Isolated Rabbit Mesenteric Preparation - An Analysis of Red Blood Cell Participation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650069 ◽

1980 ◽

Vol 44 (01) ◽

pp. 006-008 ◽

Cited By ~ 12

Author(s):

D Bergqvist ◽

K-E Arfors

Keyword(s):

Whole Blood ◽

Platelet Rich Plasma ◽

Adenosine Diphosphate ◽

In Vitro Test ◽

Pharmacological Agents ◽

Vitro Test ◽

Releasing Effect ◽

Plug Formation

SummaryIn a model using an isolated rabbit mesenteric preparation microvessels were transected and the time until haemostatic plugs formed was registered. Perfusion of platelet rich plasma gave no haemostasis whereas whole blood did. Addition of chlorpromazine or adenosine to the whole blood significantly prolonged the time for haemostasis, and addition of ADP to the platelet rich plasma significantly shortened it. It is concluded that red cells are necessary for a normal haemostasis in this model, probably by a combination of a haemodynamic and ADP releasing effect.The fundamental role of platelets in haemostatic plug formation is unquestionable but there are still problems concerning the stimulus for this process to start. Three platelet aggregating substances have been discussed – thrombin, adenosine diphosphate (ADP) and collagen. Evidence speaking in favour of thrombin is, however, very minimal, and the discussion has to be focused on collagen and ADP. In an in vitro system using polyethylene tubings we have shown that "haemostasis" can be obtained without the presence of collagen but against these results can be argued that it is only another in vitro test for platelet aggregation (1).To be able to induce haemostasis in this model, however, the presence of red blood cells is necessary. To further study this problem we have developed a model where haemostatic plug formation can be studied in the isolated rabbit mesentery and we have briefly reported on this (2).Thus, it is possible to perfuse the vessels with whole blood as well as with platelet rich plasma (PRP) and different pharmacological agents of importance.

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Kinetic Study of the Effect of Heparin on the Amidase Activity of Trypsin, Plasmin and Urokinase

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657362 ◽

1983 ◽

Vol 49 (03) ◽

pp. 199-203 ◽

Cited By ~ 10

Author(s):

V M Yomtova ◽

N A Stambolieva ◽

B M Blagoev

Keyword(s):

Kinetic Study ◽

Active Center ◽

Simultaneous Presence ◽

Amidase Activity ◽

Competitive Inhibitors ◽

Uncompetitive Inhibitor

SummaryIt was found that the effect of heparin on the amidase activity of urokinase (E C 3.4.21.31), plasmin (E C 3.4.21.7) and trypsin (E C 3.4.21.4) depended on the substrate used. No effect of heparin on the amidase activity of urokinase and trypsin was observed when Pyro Glu-Gly-Arg-p-nitroanilide (S-2444) and α-N-acetyl-L-lysine-p-nitroanilide (ALNA) were used as substrates. Heparin acted as a uncompetitive inhibitor of trypsin (Ki = 1.2×10-6 M), plasmin (Ki = 4.9×10-6 M) and urokinase (Ki = l.0×10-7 M) when Bz-Phe-Val-Arg-p-nitroanilide (S-2160), H-D-Val-Leu-Lys-p-nitroanilide (S-2251) and plasminogen, respectively, were used as substrates. These results, as well as the data obtained by studying the effect of the simultaneous presence of heparin and competitive inhibitors suggest that although heparin is not bound at the active center of these enzymes, it may influence the effectivity of catalysis.

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Inhibition of ADP-Induced Responses in Human Platelets by Agents Elevating the Cyclic AMP Level: Comparison of Aggregation and Shape Change

Thrombosis and Haemostasis ◽

10.1055/s-0038-1661208 ◽

1984 ◽

Vol 52 (03) ◽

pp. 333-335 ◽

Cited By ~ 4

Author(s):

Vider M Steen ◽

Holm Holmsen

Keyword(s):

Inhibitory Action ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Shape Change ◽

Inhibitory Effect ◽

Human Platelets ◽

Inhibitory Effects ◽

Early Step ◽

Stimulus Response ◽

Sequential Relationship

SummaryThe inhibitory effect of cAMP-elevating agents on shape change and aggregation in human platelets was studied to improve the understanding of the sequential relationship between these two responses.Human platelet-rich plasma was preincubated for 2 min at 37° C with prostaglandin E1 or adenosine, agents known to elevate the intracellular level of cAMP. Their inhibitory effects on ADP-induced shape change and aggregation were determined both separately and simultaneously. The dose-inhibition patterns for shape change and aggregation were similar for both PGE1 and adenosine. There was no distinct difference between the inhibitory action of these two inhibitors.These observations suggest that elevation of the intracellular concentration of cAMP interferes with an early step in the stimulus-response coupling that is common for aggregation and shape change.

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