Phenobarbital induction of UDP-glucosyltransferase activity in Drosophila melanogaster Meigen

The inducibility of UDP-glucosyltransferase activities towards the exogenou s substrates 1-naphthol and 2-naphthol and the endogenous metabolite xanthu renic acid was demonstrated in Drosophila melanogaster Meigen larvae and ad ults using phenobarbital as an inducer. In adults, a 3.5-fold increase of g lucosyltransferase activity toward xanthurenic acid and a 2.0-fold increase of the activity toward exogenous substrates (1-naphthol and 2-naphthol) wa s found. In larvae, maximum induction of ail three UDP-glucosyltransferase activities (2.5-fold and 1.5-fold increase of the activity toward the exoge nous and endogenous substrates, respectively) was achieved when insects, re ared on solid medium, were exposed to phenobarbital for 24 h. However, a 24 -h exposure to inducer on liquid medium yielded the same level of induction as in solid medium only for xanthurenic acid:UDP-glucosyltransferase activ ity. Repression of the activities toward exogenous substrates also was noti ced. On this medium, comparable induction to that detected on solid medium was found when inducer exposure was reduced to 2.5 h. According to the obse rved Variation resulting from the different conditions of phenobarbital tre atment, a differential induction of UDP-glucosyltransferase isoenzymes also was demonstrated. After 2.5 h of inducer exposure, three isoenzymes (every one specific for each of the three analysed substrates) were detected; whe reas, after 24 h of inducer treatment, only one isoenzyme, specific for xan thurenic acid, was detected.