Abstract

Congo red and related compounds prevent paralysis in the frog when d-tubo-curarine chloride is the curarizing agent, but not when beta-erythroidine·HCl or dihydro-beta-erythroidine·HCl is the curarizing agent. Congo red also shortens the recovery time of frogs paralyzed with d-tubocurarine chloride.

Congo red prevents the inhibition by d-tubocurarine of the response of the isolated frog rectus abdominis muscle to acetyicholine. The inhibition by the erythrina alkaloids is not prevented. Incubation with congo red potentiates the response of the frog rectus muscle to acetylcholine.

Congo red is a moderately potent inhibitor of frog brain cholinesterase activity in vitro but no inhibition was observed in vivo. Related compounds varied in their anticholinesterase activity and there was no apparent correlation between this property and their anti-d-tubocurarine activity.

Congo red and related compounds prevent the passage of d-tubocurarine through a cellophane membrane but do not affect the passage of the erythrina alkaloids. Additional evidence, i.e. precipitate formation, is presented which indicates that d-tubocurarine and congo red form a complex which is soluble or insoluble depending on the mole ratio of d-tubocurarine to congo red.

The evidence which supports the hypothesis that congo red and related compounds are effective against d-tubocurarine because of a reaction with d-tubocurarine rather than an action on a functional component of the myoneural junction is discussed.