BIOLOGICAL PROPERTIES OF THE VENOM OF THE PAPUAN BLACK SNAKE (PSEUDECHIS-PAPUANUS) - PRESENCE OF A PHOSPHOLIPASE-A(2) PLATELET INHIBITOR

The whole venom of Pseudechis papuanus, in addition to its anticoagula nt activity, powerfully inhibited platelet aggregation induced by ADP, adrenaline, collagen, ristocetin and thrombin. High levels of phospho lipase A(2) (PLA(2)) activity were detected. A mild procoagulant activ ity was also observed. Following exposure of platelets to P. papuanus venom, platelet factor 3 (procoagulant platelet phospholipid) showed d ecreased cofactor activity in factor X activation by Russell's viper, venom suggesting that the venom PLA(2) plays a major role in the inhib ition of the coagulation mechanism. In vivo rodent assays confirmed th e inhibitory effect on platelets and the haemorrhagic and neurotoxic a ctivities. It is possible that PLA(2) is responsible for anticoagulati on and that this, combined with the effect on platelet aggregation, a mild procoagulant and a moderately potent haemorrhagin, is responsible for the haemorrhagic diathesis observed in systemically envenomed pat ients. Polyvalent (Australia-Papua New Guinea) Commonwealth Serum Labo ratories antivenom, currently used for clinical treatment of snakebite in Papua New Guinea, proved highly effective against P. papuanus veno m in rodent and in vitro assays, despite the absence of this particula r venom from the immunising mixture.