Platelet aggregation induced in vitro by rabbit plasma clot-associated thrombin, and its inhibition by thrombin inhibitors.
The activation of rabbit platelets by rabbit plasma clots, and the inhibition of clot-associated thrombin by heparin:antithrombin III, recombinant hirudin (rHV2Lys47) and argatroban, a low molecular weight thrombin inhibitor, was studied. Plasma clots caused the aggregation of platelets suspended in a plasma-free medium as assessed by single platelet counting, and by scanning electron microscopy (platelet aggregates present on the clot surface). Platelet aggregation, induced by clot-associated thrombin, was inhibited by argatroban with an IC50) of 14 +/- 3 nM compared to an IC50) of 12 +/- 2 nM when human thrombin in solution titrated to give the same decrease in the platelet count as plasma clots was used. rHV2Lys47 also inhibited aggregation induced by clot-associated thrombin with an IC50 of 1.6 +/- 0.4 nM compared to 1.6 +/- 0.5 nM with thrombin in solution. Heparin was less active against clot-associated thrombin (IC50) = 69 +/- 9 mU/ml) than against thrombin in solution (IC50 = 15 +/- 5 mU/ml). This study shows that plasma clot-bound thrombin activates platelets and that direct-acting thrombin inhibitors such as argatroban and rHV2Lys47 are more effective than heparin:antithrombin III in inhibiting this phenomenon.
Gandossi
E
E
Thrombosis and Haematology Department, Cardiovascular Research, Synthélabo Recherche, Chilly Mazarin, France.
Lunven
C
C
Gauffeny
C
C
Roome
N O
NO
Berry
C N
CN
D000818:Animals; D000990:Antithrombin III / Q000494:pharmacology*; D001120:Arginine / Q000031:analogs & derivatives; D001777:Blood Coagulation; D001792:Blood Platelets / Q000187:drug effects / Q000648:ultrastructure; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008297:Male; D008855:Microscopy, Electron, Scanning; D010875:Pipecolic Acids / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011817:Rabbits; D011994:Recombinant Proteins / Q000494:pharmacology; D013449:Sulfonamides; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013925:Thromboplastin / Q000494:pharmacology
D006629:Hirudins; D010875:Pipecolic Acids; D010975:Platelet Aggregation Inhibitors; D011994:Recombinant Proteins; D013449:Sulfonamides; C064761:hirudin, Lys(47)-; D000990:Antithrombin III; D006493:Heparin; D013925:Thromboplastin; D001120:Arginine; D013917:Thrombin; C031942:argatroban