Intergenotypic effect of isopropanol ingestion in the further detoxification of ethanol and isopropanol in Drosophila melanogaster.

The effect of isopropanol ingestion on a further tolerance to ethanol and isopropanol, and its relationship with the Adh locus, have been studied using Drosophila melanogaster selected for tolerance to ethanol. For this purpose, AdhF AdhF, AdhF AdhS and AdhS AdhS flies were independently pretreated with 2 per cent isopropanol and then further exposed to solutions of 10 per cent ethanol or of 2 per cent isopropanol. Afterwards, the ability to tolerate both alcohols, and the ADH activities of the surviving flies were compared with those of flies not pretreated with isopropanol. After isopropanol ingestion, the flies of all three Adh genotypes shown much higher sensitivity to ethanol than to isopropanol although the opposite results were observed in flies not pretreated with isopropanol. Isopropanol treatment decreased the ADH activity in flies of all three genotypes within a range varying from 73 per cent (females FF) to 93 per cent (males FS), the remaining ADH activity being between 2 to 3 times higher in FF than in FS and SS flies. The reduction in ADH activity was associated with the phenomenon of ADH isozyme interconversion. After the isopropanol pretreatment, the most isopropanol tolerant flies (FF) were also the most ADH active ones. Therefore, the adaptative significance of the isozyme conversion is questioned.