Ecdysteroid formation from 25-hydroxycholesterol by arthropod molting glands in vitro

[ super(3)H]25-Hydroxycholesterol (25C) can be efficiently converted into ecdysteroids by molting glands of several arthropod species in vitro. This is shown for three crustacean and one insect species, which produce 3-debydroecdysone (3DE) as endogenous ecdysteroid. In these species, 3DE was also found as conversion product of 25C. Two other insect species, whose molting glands secrete mainly ecdysone, failed to produce ecdysteroids from 25C, but were able to metabolise 25C into 7-dehydro-25-hydroxycholesterol, which is most probably the first intermediate in 25C-conversion. Conversion into ecdysteroids (up to 80 %) was far higher than that in comparable studies using radiolabelled cholesterol as precursor (below 3%). Thus, 25C is every promising tool for the study of ecdysteroidogenesis and its regulation.