No abstract

When a tritiated ecdysone precursor, 2,22,25-trideoxyecdysone (5,8-ketodiol) was injected into larvae and pupae of Calliphora vicina, it was efficiently converted into 20-hydroxyecdysone. Injections into the anterior and posterior compartments of neck-ligated larvae have shown that both parts can hydroxylate the 5,8-ketodiol at C-25, C-22 and C-2 to form ecdysone which was readily hydroxylated at C-20 to form 20-hydroxyecdysone. When incubated with larval brain-ring gland complexes, 5,8-ketodiol was converted to ecdysone as well as to other metabolites, such as 22,25-dideoxyecdysone and 2-deoxyecdysone. Other larval tissues, namely the fat body, Malpighian tubules, gut and carcass are also able to transform 5,8-ketodiol into ecdysone in vitro, which explains the conversion of the 5Q-ketodiol injected into the abdominal portions of neck-ligated larvae. The large tissue distribution of the enzyme systems involved in the terminal hydroxylations of ecdysteroid biosynthesis in discussed in view of the results obtained in this and other insect orders. ecdysone biosynthesis, ring gland, Calliphora, blowfly, radio-labelled 5,8-ketodiol 0168-8170/87/$03.50 1Cl1987 Balaban

The effect of fenarimol, a pyrimidine-containing cytochrome P-450 inhibitor, was tested in vitro on brain-ring gland complexes of Calliphora vicina (Dipt., Calliphoridae), and on microsomes prepared from the fat body of 0-h wandering stage larvae of Neobellieria bullata (Dipt., Sacrophagidae). Fenarimol had no influence on the formation of ecdysone, but it was an effective inhibitor of cytochrome P-450-dependent ecdysone 20-monooxygenase.