Comparison of the Action Mechanisms of Gonyautoxins and Tetrodotoxi on the Cardiovascular System in the Rabbit

Abstract

We investigated the effects of gonyautoxins (GTXs) and tetrodotoxin (TTX) on cardiovascular function in 60 adult rabbits following injections of oxprenolol (β-blocker) or oxprenolol (β-blocker) and phentolamine (α-blocker). The effects of GTXs (3.0, 5.0 or 7.0 MU/kg, i. v.) and TTX (5.0, 7.0 or 11.3 MU/kg, i. v.) on cardiovascular function were assessed by measuring the electrocardiogram (ECG) and mean aortic pressure (MAP) changes in anesthetized rabbits. The ECG was monitored with A-B lead and MAP with a cathetertransducer system. In rabbits pretreated with oxprenolol (0.1mg/kg, i. v.), atrioventricular and intraventricular conduction blocks were observed but the same arrhythmia as in the intact animal was not observed after the administration of GTXs, while no remarkable effects of TTX on the cardiac function were apparent in the ECG. In rabbits treated with both phentolamine (0.05mg/kg, i. v.) and oxprenolol (0.1mg/kg, i. v.), ECG findings after the injection of GTXs or TTX were similar to those observed in the animals given only oxprenolol. GTXs induced hypotension whereas TTX had no effect on MAP except at higher dose. These results suggest that TTX depresses the sympathetic cardiac nerves and the arteriolar muscles at higher dose, while GTXs facilitate the sympathetic cardiac nerves but directly depress the cardiac and the arteriolar muscles.