Impairment of human platelet aggregation and serotonin release caused in vitro by Echis colorata venom

Aggregation of washed human platelets, induced by either ADP, thrombin or collagen, was decreased by Echis colorata venom (EVC). With ADP as an inducer, the inhibition of aggregation was proportional to the venom concentration, starting from 0.27 μg/ml and attaining full inhibition with venom concentration of 9 μg/ml. Higher concentrations were required for comparable venom effects when collagen or thrombin were used as inducers. Based on serotonin release measurements and platelet counting, it is concluded that the ECV diminished aggregation is not due to platelet lysis. Thrombin dependent serotonin release was inhibited by the venom to an extent proportional to the log ECV concentration at a range of 0.27 to 90 μg/ml. ECV effects on serotonin release are apparently independent of its effects on aggregation, since similar results were obtained either with or without EDTA. Endothelial damage and defibrination are already known to be associated with the bleeding tendency caused by ECV. The present data disclose a functional impairment of platelets as an additional antihemostatic effect of this venom.