Tityus discrepans venom produces a respiratory distress syndrome in rabbits through an indirect mechanism.

It is well known that scorpion venom induces lung lesions and respiratory distress which are usually classified as pulmonary oedema (PO). Tityus discrepans is a scorpion that lives in the north-central area of Venezuela, is the most common source of human envenomation here and produces PO. We studied the action of the venom of Tityus discrepans on whole rabbits and on their isolated lungs perfused with Krebs saline with 1 g/l of bovine serum albumin (Krebs-BSA saline). Two milligram of venom were diluted in 250 ml of solution (approximately the rabbit's total blood volume) and used to perfuse isolated lungs. Lung oedema occurred in rabbits which received 1 mg/kg of scorpion venom i.p., heparin prevented the production of this lung oedema. T. discrepans venom produced PO, in rabbits pretreated with 15 mg/kg of ajoene. Yet, Tityus venom had no effects on isolated lungs perfused with citrated or heparinized blood, and in lungs perfused with Krebs-BSA with normal Ca2+. These result show that Tityus venom does not act directly on lungs. Otherwise, we have observed that abundant microthrombi occurred in all rabbit lungs exposed to venom in vivo, suggesting that these clotting alterations are fundamental to produce PO. The presence of intravascular microthrombi is not characteristic of the usual PO hinting that scorpion venom induced pulmonary alterations are a different clinical entity. We thus propose that the use of the term pulmonary oedema in scorpionism should abandoned in favor of scorpion venom respiratory distress syndrome.