Platelet aggregation induced in vitro by rabbit plasma clot-associated thrombin, and its inhibition by thrombin inhibitors
Gandossi, E.; Lunven, C.; Gauffeny, C.; Roome, N.O.; Berry, C.N.
Thrombosis and Haemostasis 80(5): 840-844
1998
ISSN/ISBN: 0340-6245 PMID: 9843181 Document Number: 487271
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 HI in inhibiting this phenomenon.