Induction of glutathione S-transferase by phenobarbital and pesticides in various house fly strains and its effect on toxicity

The effect of phenobarbital and certain pesticides on glutathione S-transferase activity was investigated. The maximum amount of enzyme induction occurred 96 hr after phenobarbital treatment. Chlorinated hydrocarbons were more effective inducers than the other pesticides evaluated. Phenobarbital treatment did not alter the apparent K_m value but altered the $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ value of glutathione S-transferase to 3,4-dichloronitrobenzene. The amount of reduced glutathione was not increased by phenobarbital treatment. Pretreatment of house flies with phenobarbital provides some protection against methyl parathion, methyl paraoxon, azinphosmethyl, and methidathion toxicity.