Ecdysteroid Metabolism in Insects

SYNOPSIS. Remarkable development in ecdysone research has been achieved during this decade in terms of organic chemistry, biochemistry and physiology, although the problems concerning the action and behavior of ecdysteroids in target cells still remain to be solved. To elucidate the dynamics of secretion, action and inactivation of ecdysone, the metabolic pathways for ecdysteroids have been examined in several insect species and are summarized here. There may be at least three major inactivation processes for ecdysone, namely, (i) catabolic degradation, (ii) conjugate formation and (iii) epimerization to 3-epi-ecdysteroids through 3-dehydro compounds. Two means of regulation of the ecdysone titer to ensure normal development of insects are seen in Sarcophaga: (1) Enhanced epimerization of 20-hydroxyecdysone at the prepupal stage resulting in a decreasing titer of biologically active ecdysteroids. (2) Reactivation of a conjugate at the onset of adult development (a stage with an increasing titer of biologically active ecdysteroids).