Bioassay systems ecdysteroids

The various bioassay systems used for ecdysteroid structure-activity studies have been reviewed previously [120,150,171], Only those systems which have been used extensively and those which are recent are described below. 

To date, interest in the ecdysteroids has focused primarily on their role in insect molting and metamorphosis and it is perhaps somewhat unfortunate that bioassays for ecdysteroid activity have been restricted almost exclusively to evaluating their effect on the molting process. It now appears probable that molting is just one of several important regulatory functions (e.g., embryogenesis, reproduction) performed by the ecdysteroids and that we are only just beginning to scratch the surface of an insect steroid system that is equally as complex as that in vertebrate species. 

The evagination of imaginal discs of Dipteran and Lepidopteran insects is a well-characterised ecdysteroid-dependent system, which has been used by several authors to develop bioassays [183-187], However, they have been used to only a limited extent to compare the biological activities of ecdysteroids (Table 3 ). 

The early literature on ecdysteroid structure-activity studies has been reviewed [120,150,171], The various bioassays employed vary in their complexity of performance and interpretation. A number of factors can affect the potency of a test compound to a greater or lesser extent depending on the assay system penetration, metabolism, excretion rate, sequestration and target site activity. In vivo assays will give a measure of all of these acting in concert, but not allow the individual contributions to be identified. On the other hand, cell-free receptor assays probably give a direct measure of target activity, but may bear little resemblance to the in vivo situation. 

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