EFFECTS OF SCORPION-VENOM ON CENTRAL AND PERIPHERAL CIRCULATORY RESPONSE IN AN OPEN-CHEST DOG-MODEL

Scorpion venom can induce in dogs severe haemodynamic changes leading to rapid rise in systemic blood pressure and cardiac output, followed by reduction of cardiac output and blood pressure within 1 h. The decr ease in cardiac output is not related to myocardial dysfunction (Taras iuk et al. 1994). We hypothesized that scorpion venom affects cardiac output by reducing venous return to the heart. Venous return was studi ed by steady-state measurements of cardiac output, the pressure gradie nt and resistance to venous return, in 16 dogs following injection of 0.05 mg kg(-1) venom obtained from the scorpion species Leiurus quinqu estriatus. In eight of the 16 dogs, atropine (0.1 mg kg(-1)) was given 15 min prior to venom injection (n = 4) or 85 min (n = 4) after venom administration. In five additional dogs, the stability of the prepara tion over time was evaluated following the same protocol without the i njection of the venom. At 15 min, the venom induced an increase in blo od pressure (80%) and cardiac output (250%) (P < 0.001) with little ef fect on heart rate. At 90 min, cardiac output and heart rate declined considerably below baseline (P < 0.001). Atropine prevented the decrea se in heart rate, but did not affect the reduction of cardiac output. Five minutes after venom injection, mean circulatory pressure increase d by 300% (P < 0.001), which was accompanied by a rightward shift of t he venous return curve with no effect on resistance to venous return. At 120 min, mean circulatory pressure recovered and resistance to veno us return remained at 40% (P < 0.01) above baseline. This study indica tes that, in dogs, scorpion venom affects cardiac output by modifying the determinants of venous return. The initial increase in cardiac out put is related to increased mean circulatory pressure since resistance to venous return did not change. The later fall in cardiac output. is related to the reduction of mean circulatory pressure and increased r esistance to venous return.