Ecdysone metabolism in the tick Ornithodoros moubata (Argasidae, Ixodoidea)

The metabolism of injected [3H]ecdysone was studied in final-instar nymphs of Ornithodoros moubata (Murr.) at different stages of the moult cycle in the laboratory in Switzerland. After extraction from haemolymph or whole ticks, 5 radioactive fractions were detected by high-performance liquid chromatography. Fraction 1 contained unknown metabolites less polar than ecdysone. Fraction 2 corresponded to the injected ecdysone, and fraction 3 was ecdysterone. Fraction 4 might have been 20,26-dihydroxy- alpha -ecdysone, and fraction 5 contained polar ionisable metabolites of as yet unknown chemical nature. It is suggested that metabolism of the labelled ecdysone proceeds through hydroxylation at C20 and probably hydroxylation at C26 to 20,26-dihydroxy- alpha -ecdysone which then yields apolar and polar end-products. In addition, ecdysone and ecdysterone may be directly converted to apolar and polar metabolites. The formation of polar end-products became very prominent 7-9 days after feeding, when the endogenous ecdysteroid titre fell.