Inhibitors of ester hydrolysis as synergists for biological activity of Cecropia juvenile hormone.

In Manduca sexta pupae the sensitivity to exogenous Cecropia C18 juvenile hormone (JH) is governed in large part by the rate at which the hormone is metabolized. By analysing the distribution of labelled JH and its metabolites, when dispensed by injection in light mineral oil, I have shown that the half-life of JH at concentrations ranging from 0·02 to 1 μg/g live weight of insect is approximately 24 hr.When the same doses of JH are dispensed in mineral oil containing endocrinologically inactive carboxylesterase inhibitors, organophosphate, and carbamate insecticides, the hormone's half-life in certain cases is prolonged significantly. The formulations containing those materials which most effectively prolong the hormone's half-life give higher assay scores than equivalent doses of hormone in mineral oil alone.From these results it is inferred that the chemicals tested synergize the Cecropia juvenile hormone's biological activity by serving presumably as inhibitors of the principal enzyme responsible for the rapid breakdown of exogenous C18-JH in haemolymph—a carboxylesterase. Preliminary in vitro experiments with carboxylesterase-rich Manduca pupal blood further support this inference.