Toxic action of organophosphorus compounds and esterase inhibition in houseflies

Abstract

The paper deals with investigations on the inhibition in vivo of the cholin-esterase and the aliesterase in houseflies poisoned by treatment with organophosphorus insecticides. The kinetics of the inhibition of esterases by DDVP, paraoxon and diazoxon in the presence and in the absence of substrate were closely studied. It was found that the inhibition is strongly retarded by the presence of acetylcholine in the case of the cholinesterase, and of phenylbutyrate in the case of the aliesterase. It could thus be shown that the addition of these substrates at the time of homogenization lends appropriate protection to the enzymes against free inhibitor present in the body of the insect. The results obtained with this “protective method” show that cholinesterase inhibition at the time of knock-down was generally less than 50 per cent, whereas the aliesterase inhibition at this time proved to be about 90 per cent. It could further be shown that the in vivo aliesterase inhibition increased rapidly from the beginning of exposure of the flies to the insecticide, and reached values of more than 50 per cent even long before knock-down occurred. This inhibition was found to be not readily reversible in vivo.