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

Abstract

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.

Ecdysteroid metabolism in crustaceans

“…The major ecdysteroids identified in the hemolymph of decapod crustaceans are ecdysone, 20E, 3D20E, and PA, but the specific compounds and their levels vary between species, developmental stage, molt stage, and season [32,44,48,49,61,64,66,67,70,78,81,82,87,93,97]. In stone crabs (M. mercenaria) that have been eyestalk ablated to activate the YO, 20E, 3D20E, and PA are present in about equal amounts; a fourth large peak eluting from a reverse-phase column was not identified [32].…”

“…The primary site for excretion of ecdysteroids is the antennal gland. In lobster (Homarus americanus), between 81% and 96% of excreted ecdysteroids is in the urine, depending on the molt stage; the remainder is in the feces [66,97]. In crayfish (O. limosus), there is a preferential excretion of ecdysone over 20E.…”

“…In insects, 20E is inactivated by a cytochrome P450 26-hydroxylase [100,101]. In decapod crustaceans, a 26-hydroxylase activity in various tissues converts 20E to 20,26-dihydroxyecdysone (20,26E) and PA to inokosterone (25-deoxy-20,26-dihydroxyecdysone or 25d20,26E) [63,[65][66][67]97]. Oxidation at the C26 forms ecdysonoic acids (EAs).…”

“…Oxidation at the C26 forms ecdysonoic acids (EAs). For example, 20E and PA are metabolized to 20-hydroxyecdysonoic acid (20EA) and 25-deoxy-20-hydroxyecdysonoic acid (25d20EA), respectively, and are excreted in the urine [65][66][67]97,102]. Ecdysteroids can also be converted to their 3␣-hydroxy epimers by peripheral tissues.…”

“…Various tissues can convert ecdysteroids and their metabolites to highly polar (HP) conjugates, which can be excreted in the urine [61,63,65,66,97]. The levels of HP conjugates vary over the molt cycle and can at times be the predominant ecdysteroid in the hemolymph [61,77,82,87,88,93].…”