Hydrolysis of pyrethroid insecticides by soluble mouse brain esterases

trans-Permethrin, a pyrethroid insecticide, was hydrolyzed by one or more carboxylesterases located in the soluble fraction of mouse brain homogenates. The apparent affinity of this activity for trans-permethrin was greater than that reported for mouse hepatic carboxylesterase activity, but the apparent maximum velocity was considerably lower than that of the hepatic activity. Soluble brain esterases also hydrolyzed several other pyrethroid esters with a substrate specificity different from that of the hepatic esterases. In particular, alpha-cyano-3-phenoxybenzyl esters of noncyclopropane acids (e.g., fenvalerate and fluvalinate) were hydrolyzed by brain esterases at rates equal to or greater than that measured for trans-permethrin. These results suggest that hydrolysis in the brain may contribute to the detoxication of some pyrethroids in mammals.