PLATELET ACTIVATION DURING Bothrops jararaca SNAKE ENVENOMATION IN RABBITS

SANTORO, M.L.(1), BARBARO, K.C.(2), ROCHA, T.R.F.(3), SANO-MARTINS, I.S.(1)

(1)Laboratory of Pathophysiology and (2)Immunopathology, Instituto Butantan, and (3)Laboratory of Thrombohemorrhagic diseases, HCFMUSP, São Paulo, Brazil.

Despite being well established that Bothrops jararaca snake venom causes blood coagulation and fibrinolysis disturbances, scant information is available about blood platelet disorders. In a previous investigation, we observed decreased numbers of dense bodies in circulating platelets of experimentally envenomed rabbits, suggesting that they underwent platelet activation. Herein we show that rabbits – whose platelets were previously labeled ex vivo with NHS-biotin – injected intravenously with B. jararaca venom (60 µg/kg) presented thrombocytopenia, hypofibrinogenemia, elevation of von Willebrand factor plasma levels, platelet hypoaggregation, decreased platelet ATP secretion, normal plasma levels of platelet factor 4, and invariable intraplatelet serotonin content. By flow cytometry, platelets displayed a significant decrease on the expression of a GPIIb-IIIa epitope recognized by P2 monoclonal antibody, but total GPIIb-IIIa expression, evaluated with specific polyclonal antibodies, was normal. Fibrinogen or fibrin degradation product (FDP) expression on platelet surface showed no significant alteration. Nonetheless, significant elevations of platelet P-selectin and of a ligand-induced binding site of GPIIIa were noted on circulating platelets. The percentages of circulating reticulated platelets, as well as platelet survival, of envenomed rabbits were not statistically different from control animals. We suggest that thrombin generated by procoagulating components of B. jararaca venom has an essential role in the pathogenesis of platelet and coagulation disorders in this experimental model. Increased expression of P-selectinin the experimental group demonstrates that platelets of envenomed rabbits are indeed activated in the circulation and that decreased fibrinogen or increased FDP levels are not the primary cause of the platelet dysfunction observed in bothropic envenomation.

CORRESPONDENCE TO:

KatiaCristina Bárbaro, Rua Fernandes Moreira, 460 Apto. 133, São Paulo, SP, CEP: 04716-000, Brasil, Email: kbarbaro@usp.br