Moulting hormone ecdysteroids

Effect of Ecdysteroids Brassinosteroids are structurally related to the insect moulting hormones, the ecdysteroids. Thus the question was raised whether... 

The similarity of ecdysteroids and brassinosteroids may cause some difficulties in their definition. Ecdysteroids were initially defined as "all compounds structurally related to ecdysone" (3). This definition would include brassinosteroids. Recently an attempt has been made by Lafont and Horn to redefine ecdysteroids (6). According to their definition one may "distinguish between true ecdysteroids as compounds where the steroid bears a cis-fused A/B ring junction, a 7-ene-6-one chromophore and a 14a-OH (irrespective of activity in a moulting hormone assay) and ecdysteroid-related compounds which do not fulfil all the above criteria (either they lack the 14a-OH, or the 7-ene, or they present one additional 4- or 14-ene double bond, etc.)" (6). The latter group would include brassinosteroids. Unfortunately, comparable definitions of brassinosteroids are not available so far. 

Some of the most interesting insect phytosterol derivatives are the so-called moulting hormones or ecdysteroids (Fig. 23.17) (Hirino and Hirino, 1970). The first ecdysteroid (25... 

More sterically hindered steroids and, in particular, the polyhydroxylated compounds were more efficiently derivatized with trimethylsilylimidazole. The ease of silylation of the ecdysteroids (polyhydroxylated anthrapod moulting hormones) tracked the following order 2, 3, 22, 25 > 20 14. Those substances containing a 14a-... 

In some arthropods (for this hormone is shared with other classes besides insects), the series are not hydroxylated at C-25. Many crustaceans use 20-hydroxyecdysone as moulting hormone, others use ponasterone A (Figure 7.14). Ecdysteroids have also been found in plants. These phytoecdysteroids are widely distributed in the plant... 

In decapod crustaceans, the production of ecdysteroids by the Y-organs is inhibited by moult-inhibiting hormone from the eye-stalks [21,22], The ecdysteroids released are E (2-1), 25dE (2-2) and 3DE (2-9), which are converted to 20E (1-1) and poA (2-7). Although elevated levels of ecdysteroids are associated with ovarian maturation and eggs of decapod crustaceans, their functions have not yet been elucidated. 

There are several reports that cHH can inhibit the ecdysteroid synthesis by YO in vitro but that MIH cannot act as a cHH by increasing glucose concentration (see for example [108]). It was probably this multifunctionality of cHH that led to it being mistaken for MIH in certain instances. Why should cHH duplicate the role of another hormone during the moult cycle The definitive answer to this question is still not known but specific receptors for cHH (along with MIH-specific receptors) have been demonstrated, by classical membrane binding studies, to be present on the YOs of intermoult brachyuran crabs [84]. Unlike cHH, radiolabelled MIH binds only to membrane preparations of YOs and not... 

---