Moult-inhibiting hormone

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. 

Most of the more recently described allenic steroids bear an allene group at the 17-position, which was usually formed by an SN2 substitution [106] or reduction [86d] process of a suitable propargylic electrophile. Thus, reduction of the pro-pargylic ether 109 with lithium aluminum hydride followed by deprotection of the silyl ether resulted in the formation of the allenic steroid 110, which irreversibly inhibits the biosynthesis of the insect moulting hormone ecdysone (Scheme 18.35) [107]. 

Nonneurotoxic insect growth regulator with contact and stomach action. Exhibits a strong juvenile hormone activey, inhibiting metamorphosis to the adult stage and interfere with the moulting of early instar larvae... 

The action of /J-exotoxin induces a group of phenomena completely different from that of endotoxin, proceeded according to a different mechanism. The effect is manifested by teratological phenomena, inhibited pupation, mortality after moulting, and malformation. Therefore, the assumption of several authors seemed to be justified that /S-exotoxin affects the activity of formation of hormones regulating the metamorphosis of insects. On the other hand, the nucleotide structure indicates that /3-exotoxin exerts its action as a nucleic acid antimetabolite (Benz, 1966 Grebelsky and Kandybin, 1974). 

A few steroid compounds, which only partly meet the indispensable structural requirements for moulting hormone activity were found to inhibit post-ecdysial hardening and sclerotisation of the insect cuticle (Horn et al.. 1966 Velgova et al.,... 

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... 

One of the most useful of the insect hormone antagonists is diflubenzuron (4.81), which is l-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea. It prevents moulting in flies and mosquitoes by inhibiting formation of the enzyme that converts UDP-acetylchitosamine to chitin, an inhibition that leads to slow death. It also inhibits egg hatching and, for larviporous insects such as the African tsetse fly, no viable offspring appears. It is harmless to Man (Jordan and Trevern, 1978). 

Moulting Hormones - The structure of ponasterone B and C (24), the synthesis of A and its identity with crustecdysone (25) have been reported > > f Similar hormones are podecdysone A and the amarasterones . The synthesis of active pregnan-6-ones has appeared and some effects of ecdysone and analogs on the development and reproduction of insects were published . Inhibition of larval growth and development was seen with several ecdysone... 

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