ECDYSTEROID FORMATION FROM 25-HYDROXYCHOLESTEROL BY ARTHROPOD MOLTINGGLANDS IN-VITRO

[H-3]25-Hydroxycholesterol (25C) can be efficiently converted into ecd ysteroids by molting glands of several arthropod species in vitro. Thi s is shown for three crustacean and one insect species, which produce 5-dehydroecdysone (3DE) as endogenous ecdysteroid. In these species, 3 DE was also found as conversion product of 25C. Two other insect speci es, whose molting glands secrete mainly ecdysone, failed to produce ec dysteroids 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 highe r than that in comparable studies wing radiolabelled cholesterol as pr ecursor (below 3%). Thus, 25C is a very promising tool for the study o f ecdysteroidogenesis and its regulation.