Abstract: Objective: To observe that cobra venom factor (CVF) isolated from the venom of Naja naja atra induces platelet aggregation in platelet rich plasma (PRP) and gel-filtered platelet suspension (GFP). Methods: In vitro platelet aggregation in PRP and GFP was quantified turbidimetrically with computer-controlled aggregometer. Results: CVF 195 nmol·L^-1 induced a slow aggregation following an obvious metamorphosis of platelets in rat PRP but not in GFP and in other species. CVF-induced rat platelet aggregation depended on extracellular Ca²⁺ and complements, and was not affected by indomethacin 100 mmol·L^-1. Ni²⁺ 3 mmol·L^-1 attenuated the maximal velocity of aggregation (S) without influence on the maximal extent of aggregation (A) of CVF-induced rat platelet aggregation while tetrodotoxin 40 mmol·L^-1 attenuated A without influence on S. Conclusion: CVF, a complement activator, elicits slow rat platelet aggregation following an obvious metamorphosis, which depends on Ca²⁺ and Na⁺ influx, complements and is unrelated to thromboxane (TXA2) pathway.

Key words: Cobra venom factor, Platelet aggregation, Complements, Calcium ion