Metabolism and Excretion of Injected [3H]-Ecdysone by Female Lobsters, Homarus americanus

The dynamics of ecdysteroid metabolism and excretion were followed in adult lobsters, Homarus americanus. Females at five different molt stages were injected with [3H]-ecdysone. Levels of [3H]-20-hydroxyecdysone (20E), converted from [3H]-ecdysone, rose rapidly and remained significantly higher in premolt stages D0 and D1. In contrast, significant increases in the levels of highly polar ecdysteroid metabolites (HP) occurred primarily in stages A and C. Changes in the hemolymph levels of 20E and HP in hemolymph over the molt cycle suggest additional metabolic mechanisms by which the titers of active molting hormones can be regulated. Excretion of [3H]-ecdysteroids was slower during early premolt stages D0 and D1, suggesting that this reduced rate may be an additional mechanism for regulating ecdysteroid titers. Study of [3H]-ecdysteroids indicated that metabolism proceeds primarily to HP that are excreted in the urine with unaltered ecdysteroids. An additional ecdysteroid metabolic route was found in the midgut gland; this route removes ecdysteroids from the hemolymph and transforms them into apolar metabolites prior to their excretion in the feces. This route is similar to that previously found for ingested [3H]-ecdysone, which was converted to apolar conjugates without further absorption.