Metabolism of 20-hydroxyecdysone in adult Drosophila melanogaster

Yolk protein synthesis can be induced in male Drosophila melanogaster by the injection of high doses of 20-hydroxyecdysone, but the response is short-lived with the rate of yolk protein synthesis reaching a peak at 8–12 hr after injection, and declining to barely detectable levels after 24 hr. The injected 20-hydroxyecdysone was rapidly metabolised in vivo to compounds of higher polarity, with as little as 17% of the original steroid remaining within 10 min of a 480 ng injection, of which about 60% was in the form of more polar metabolites. These metabolites were inactive at inducing yolk protein synthesis when injected into previously untreated male flies, at a concentration where 20-hydroxyecdysone reproducibly induced yolk protein synthesis. In in vitro incubations of isolated fly regions the limited amount of metabolism observed was towards compounds of lower polarity than 20-hydroxyecdysone, tentatively identified as acetyl derivatives rather than the pattern of highly polar metabolites observed in vivo .