Studies on the Mode of Action of Organophosphorus Compounds

It was presumed in the previous paper that sumithion was easily absorbed from the gastrointestestinal tract, similarly to methylparathion, following the oral administration to mammals. Inhibition of blood and brain cholinesterase of Guinea pigs and white rats in vivo after oral treatment with sumithion and methylparathion was determined. Inhibition of the enzymes was found to proceed rather rapidly and in most cases it reached maximum within one hour. Sumithion hindered the brain cholinesterase activity far less effectively than methylparathion. Intravenous administration of these phosphorothioates and their oxygen analogs clarified that the latters were more inhibitory on the cholinesterases and that of the two oxygen analogs, sumioxon was less effective. The poor susceptibility of the brain enzyme to sumithion was also observed in this case. This paper deals with the experimental results and their possible implications in the toxicity of the organophosphorus compounds toward mammals.