The Precocene Antijuvenile Hormones (Allatotoxins): A Case History in Insect Toxicology
The precocenes (ageratochromenes) have attracted attention as the first examples of simple molecules, superficially dissimilar in structure to the natural juvenile hormones (JHs) yet able to elicit remarkable JH-antagonistic effects in some species of insects. Precocenes appear to exert a cytotoxic action on the corpora allata (CA), mediated by an oxidative bioactivation in vivo. Reactive epoxide formation in the CA is the mechanism that currently best explains the results of several radiochromatographically based metabolism studies in precocene-sensitive insects. Other oxidatively derived reactive intermediates such as quinone-methides or oxyradicals have been suggested but these mechanisms await substantiation. The limited pharmacokinetic studies on precocenes conducted so far have not revealed differences that convincingly explain their species selectivity but methods must be found to maintain the bioavailability of parent precocenes to the CA for longer periods, especially in the seemingly insensitive larvae of lepidoptera.
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