Variability of neurotoxicity of and lack of tolerance to the anticholinesterases soman and sarin in the rat.

The neurotoxicity and lethality of Soman and Sarin, after single and repeated treatment at 50-60% of their LD50 doses in rats were investigated. Single treatment with Soman (100 micrograms/kg) and Sarin (120 micrograms/kg) produced severe tremors, convulsions and hypothermia, in some rats only, while the others did not show toxicity, i.e. an all or none effect. Soman and Sarin (100-120 micrograms/kg) caused, respectively, 89-93% and 26-48% inhibition of AChE at 6 hr and 56-68% and 17-39% inhibition at 24 h after single injections. Repeated treatment with Soman (90 micrograms/kg) and Sarin (100 micrograms/kg) at 4 day intervals caused variable incidences of neurotoxicity and increasing mortalities, and after ten injections the survival rates were 31 and 54%, and AChE inhibition was 86 and 75%, respectively. It is suggested, that the variable neurotoxicity of and the low tolerance to of these compounds are partly related to peripheral dispositional mechanisms. Furthermore, the profile of toxicity of these anticholinesterase agents should be differentiated from, but not generalized with, that of the other anticholinesterase organophosphates.