METABOLISM OF ALPHA-ECDYSONE IN INTERMOLT LAND CRABS (GECARCINUS-LATERALIS)

The metabolic fate of α-ecdysone was examined in intermolt crabs to elucidate the biochemical pathways as well as the dynamics of ecdysteroid metabolism. At 1-24 hr after injection of α[3H]ecdysone, metabolites were extracted from each of five tissues and separated by reverse-phase chromatography. Ecdysone metabolism proceeded through (i) sequential hydroxylation at C-20 and C-26, and (ii) formation of glycosidic conjugates of the free ecdysteroids. The conversion of α- to β-ecdysone (20-hydroxyecdysone) was very rapid; within 1-4 hr, over 50% of the radioactivity was present as β-ecdysone. Further hydroxylation to 20,26-dihydroxyecdysone was less rapid, but continuous over the experimental period. Fractions of each of the three ecdysteroids were conjugated, probably as β-glycosides. These conjugates comprised 20% of the total radioactivity in the crab, over half of which was concentrated in the midgut gland and hindgut. Free and conjugated ecdysteroids, as well as an extremely polar material which was resistant to enzymatic hydrolysis, were excreted in both the urine and the feces. The rate of elimination of total radioactivity and the rate of turnover of β-ecdysone were fairly rapid but varied among the different tissues. The rate of turnover in the epidermis was very rapid (k ∼ 0.08 hr-1). Turnover in the carcass and the whole crab was slower (k ∼ 0.02 hr-1), perhaps due to sequestration of some of the metabolites in tissues which are inactive in the metabolism of ecdysteroids. © 1979.