Alterations of the blood coagulation system after accidental human inoculation by Bothrops jararaca venom.

Blood coagulation studies carried out on 78 patients up to 30 h after they were bitten by Bothrops jararaca snakes demonstrated clotting defects in 37 patients which included afibrinogenemia, reduced levels of prothrombin, of factors V and VIII, thrombocytopenia and activation of the fibrinolytic system. Factor IX and X levels were within normal range for all patients. These in vitro data suggest that the disseminated intravascular clotting observed in vivo following envenomation may be triggered by the intravascular release of patient thrombin by snake venom enzymes.

The anticoagulant effect of Bothrops castelnaudi snake venom (Castelnaud's pit viper).

An inhibitory effect of Bothrops castelnaudi venom was observed on the following systems: prothrombin time, activated partial thromboplastin time, thrombin time, thromboplastin generation time, activation of factor X by Russell's viper venom and Russell's viper venom activated factor X (factor Xa). This effect did not require previous incubation and was prevented by the addition of Bothrops-antivenom. The prolonged activated partial thromboplastin time was not shortened by increased phospholipid concentration (0.5-10 mg/ml), suggesting that the inhibitory effect is not due to an anti-phospholipid activity. No significant fibrinogenolytic activity was detected upon incubation of human fibrinogen with the venom, since physiological levels of thrombin-clottable material were still present. Compared to Bothrops jararaca venom, the proteolytic activity on casein and on azocoll was very low. Thrombin-induced clots of human plasma and fibrinogen were not lysed by the venom within 24 hr. The results indicate that the anticoagulant effect of Bothrops castelnaudi venom is exerted at least at two levels of the blood coagulation mechanism: (1) before prothrombin activation, by inhibiting factor X-activation and factor Xa activity; (2) by direct action on thrombin.

The inactivating effect of Bothrops jararaca and Waglerophis merremii snake plasma on the coagulant activity of various snake venoms.

Plasmas of the poisonous snake Bothrops jararaca and of the non-poisonous snake Waglerophis merremii were not clotted by various snake venoms. These plasmas also inactivated venom clotting activity on human plasma. This effect was absent in snake serum and in heated snake plasma. The active fraction was isolated by gel chromatography from B. jararaca plasma and corresponded to the fibrinogen-containing fractions. It is suggested that the inactivation by snake plasma of the venom coagulant activity might be due to a fibrinogen-bound complex or to fibrinogen itself.

Use of semipermeable polyurethane membrane for skin graft dressings.

The use of semipermeable polyurethane membrane (Op-site) for skin graft donor-site dressings is now well-accepted. We have used Op-site for skin graft coverage in 25 patients with good results. The dressing modality is not only easy to do, even in anatomically difficult areas, but it also maintains a moist environment, allows daily graft observation, and provides a barrier for exogenous bacteria.

Thrombin-like and factor X-activator components of Bothrops snake venoms.

A comparative study on the coagulant activity of snake venoms was carried out in 26 Bothrops species, using specific clotting systems for the thrombin-like and the factor X-activator activities. With only two exceptions (B. erythromelas and B. castelnaudi) all venoms showed thrombin-like activity, since they were able to clot fibrinogen directly. The absence of thrombin-like action of B. erythromelas venom is due to a fibrinogenolytic effect. Five venoms (B. atrox asper, B. bilineatus bilineatus, B. cotiara, B. fonsecai and B. itapetiningae) were unable to produce a prothrombin activator when preincubated with serum, factor V, and phospholipid. None of the venoms seems to require factors VII, VIII, IX, XII and XIII for their complete coagulant action. Direct prothrombin activation was observed in most of the Bothrops venoms, alone or combined with thrombin-like and factor X-activator activities. An anticoagulant activity was exhibited by B. castelnaudi venom, probably due to an anti-Xa action. This study points out that the coagulant activity of snake venoms varies within the same genus and must be characterized for each species. Thus, in Bothrops venoms the thrombin-like and factor X-activator components are not always associated, the coagulant effect may be related only to one of the components.