ECDYSONE METABOLISM AND THE INTERRUPTION OF PROECDYSIS IN THE LAND CRAB, GECARCINUS LATERALIS

¹ University of Tennessee, Oak Ridge Graduate School of Biomedical Sciences, Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830

1. The metabolic fate of injected [³H] ecdysone was examined in crabs in premolt stage D₀ and in crabs at this stage whose proecdysis was interrupted by re-autotomy of partially regenerated limbs at the time of injection.

2. In both sets of crabs, 20-hydroxyecdysone was the principal metabolite, with further hydroxylation to 20,26-dihydroxyecdysone and the formation of polar conjugates (primarily in the midgut gland) occurring to a limited extent.

3. The rate of elimination of 20-hydroxyecdysone from normal crabs in stage D₀ is slow (k = 0.002/hr). Within a few hours after re-autotomy of partial regenerates from crabs in stage D₀, the rate of loss of 20-hydroxyecdysone from the whole crab increases by tenfold, while the loss from the serum accelerates twentyfold.

4. The increased rate of loss of 20-hydroxyecdysone from the re-autotomized crabs is associated with an increased amount of catabolism to polar inactivation products. The increase in the rate of elimination of ecdysteroids is sufficient to account for the observed decrease in endogenous ecdysteroid titers when proecdysis is interrupted by this re-autotomy.