Direct vs. mediated effects of scorpion venom: an experimental study of the effects of a second challenge with scorpion venom.

Abstract

To assess the respective roles of venom and of catecholamines following scorpion envenomation and to verify whether a second challenge with scorpion venom induces the same consequences than a first one. Controlled animal study in a university research laboratory. Anesthetized and ventilated dogs. Fifteen dogs received intravenously a sublethal dose of scorpion venom (0.05 mg/kg). In the reenvenomated group (n=5) a second venom challenge with one-half sublethal venom dose was performed 30 min after the first one. The control group (n=10) received saline. Five additional animals served as sham. Plasma toxin and catecholamine levels and a set of usual hemodynamic measurements were repeatedly measured in the first hour following envenomation. In the reenvenomated group another set of measurements was performed 5 min after the second challenge. Changes in toxin, catecholamines, and the main hemodynamic parameters were compared between the study groups. Initial peak toxin levels were similar in the two groups. They induced a striking increase in circulating catecholamines, a fall in heart rate, and an increase in mean arterial and pulmonary artery occluded pressures and in systemic vascular resistance. In the reenvenomated group the second challenge with scorpion venom achieved a toxin blood level similar to the first peak. However, it was not associated with a significant effect either on catecholamines release or on hemodynamics. Subsequent trends in hemodynamic changes were similar to those observed in the control group. These data emphasize the limited role of direct effects of scorpion venom on the cardiovascular system and the key role of catecholamines.