Marine toxins from the Pacific—IX: Some effects of ciguatoxin on isolated mammalian atria

Abstract

Ciguatoxin produced an initial negative inotropic and chronotropic effect which was followed by a positive inotropic and chronotropic effect on the isolated rat atria. The initial depression could be effectively blocked by atropine (1 × 10 −7 g per ml), and partially blocked by hexamethonium or hemicholinium-3 (2 × 10 −5 g per ml). The positive inotropic and chronotropic action of ciguatoxin was reduced by pretreating the atria with MJ-1999 (1 × 10 −6 g per ml) or guanethidine (1 × 10 −6 g per ml). Abolition of the response to ciguatoxin could also be accomplished with a single dose of 2 mg per kg of reserpine given to the rat 24 hr before isolating the heart. It is not yet possible to correlate inotropic and chronotropic effects of the toxin with the release of catecholamines, but it seems likely that excitatory effect of the toxin may be elicited by a release of catecholamines from their stores.