Enhanced in vitro metabolism of testosterone by microsomes from insecticide-resistant Spodoptera littoralis larvae

Abstract In vitro testosterone hydroxylation was compared between susceptible and insecticide-resistant Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) larvae. The susceptible larvae were topically applied with a non-lethal dose of lindane (γ-HCH) and the effects on microsomal P 450 were studied within the 48 h following treatment. In vitro testosterone hydroxylation by phenobarbital-induced rat liver microsomes was used as a biological standard to investigate the functional role of P 450 isozymes in S. littoralis . Depending on either the strain or the treatment, various amound of identical hydroxylated derivatives of testosterone were formed. Lindane increased cytochrome P 450 content in susceptible S. littoralis but isoforms specific for testosterone hydroxylation were unaffected or even inhibited. In contrast, most of testosterone hydroxylase activities were enhanced in the resistant strain, uggesting either that not only xenobiotic-specific cytochromes P 450 were overproduced, or that overproduced cytochrome P 450 forms were not only specific for xenobiotics.