Effect of route of exposure and repeated doses on the acute toxicity in mice of the cyanobacterial nicotinic alkaloid anatoxin-a.

Anatoxin-a (ANTX-a) is a potent nicotinic cholinergic alkaloid produced by some toxigenic strains of cyanobacteria. We have examined i.p. and oral LD50 values of two ANTX-a producing Anabaena sp. and synthetic (+)-ANTX-a in outbred Swiss Webster mice. All three appeared equivalent by i.p. injection, but Anabaena flos-aquae NRC-44-1 was approximately twice as potent orally as the other two. Additionally, we were unable to demonstrate development of any biologically significant tolerance to acute ANTX-a exposure using two different repeated dose regimens.