[Autonomic effects of scaritoxin in the cat and guinea pig. Cardiac protection by an anti-arrhythmia agent].

A purified extract from the muscles of the fish Scarus gibbus (93% scaritoxin and 7% ciguatoxin) was tried on anesthetized cats and isolated guinea-pig atria. Intra-venous injection to cats (10, 20 and 40 mg/kg) induced deep respiratory depression, inhibition of duodenal contractions, increased salivary secretion, mydriasis and lacrymal secretion. Heart rate was slowed by 17 to 44 per cent. Impaired cardiac conduction led to different types of blocks. On the contrary, cardiac excitability was enhanced, as evidenced by the occurence of many auricular and mostly ventricular extra-systoles, often evolving into long periods of ventricular paroxysmal tachycardia. The rate of contraction of isolated guinea-pig atria was equally depressed and this effect was antagonized by atropine. The duration of the refractory period was shortened; an inotropic effect was observed and the action of acetylcholine was potentiated by the toxin. Cholinesterase inhibition by scaritoxin, previously mentioned in other papers, is thus evidenced. Mydriasis and duodenal inhibition may be tentatively explained by a nicotinic effect on the sympatheticoadrenal system. This mechanism may be responsible for cardiac inotropic action and increased excitability. Other mechanisms may be suggested, including a possible digitalis-like effect due to a cyclopentanone ring in the scaritoxin molecule. Interestingly, intra-venous injections of the antiarrythmic drug procainamide (20 to 30 mg/kg) could either prevent or reverse the signs of cardiac hyperexcitability in the anesthetized cat. However, death results usually from respiratory depression, the intimate mechanism of which is not yet known.