Injection of labelled ecdysone and 20-hydroxyecdysone into Pieris pupae showed that their catabolism proceeds through 26-hydroxylation followed by conversion into acidic steroids assumed to be 26-oic compounds. This biological system is characterized by the lack of conjugation reactions and by rather long-lived hormones. In vivo biosynthesis of ecdysteroids was investigated by 24 hr [3H]cholesterol labelling, followed by HPLC analysis of the resulting [3H]ecdysone and 20-hydroxyecdysone. Active conversion (up to 0.07% in 24 hours) was observed between 48 hr and 120 hr following pupal ecdysis, a result in good agreement with the variations observed in hormone content. Long-term [3H]cholesterol incorporation experiments made it possible to monitor ecdysteroid dynamics during pupal development. Three periods were observed, corresponding to the successive accumulation of ecdysone, 20-hydroxyecdysone and an acidic metabolite. Comparison of these results with those of the experiments involving labelled ecdysone injection shows that the catabolism of injected hormones is not the same as that of endogenous hormones. © 1981.
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