Haemorrhagic activity of neotropical rattlesnake (Crotalus vegrandis Klauber, 1941) venom.

In this work we have demonstrated for the first time in any Venezuelan Crotalus, haemorrhagic activities that are present in the Neotropical Uracoan rattlesnake (Crotalus vegrandis) venom. This venom has been little studied, perhaps because the snake is restricted to a small habitat located in the dry savannahs of northeastern Venezuela. In our experiments Crotalus vegrandis venom caused a very evident haemorrhagic area consisting of approximately 2/3 diameter of the area caused by a positive control Bothrops lanceolatus venom. Crotalus vegrandis venom affects blood coagulation and causes intense haemorrhages. It does not clot fibrinogen, therefore it has neither thrombin-like activity which transforms fibrinogen to fibrin nor procoagulant enzymatic function which produces thrombin. On the other hand, it degrades fibrinogen making it incoagulable to thrombin. The venom, when injected in the animals, resulted in a high increase of the Partial Time of Thromboplastin (PTT) tests. It is interesting to observe that the haemorrhagic capacity in the Crotalus genus (widely distributed in the American continent) increases from south to the north, being present in North American Crotalus, a venom with wide haemorrhagic activities, and almost non-existent in most of the South American Crotalus species and subspecies.