The influence of forskolin on the metabolism of ecdysone and 20-hydroxyecdysone in isolated fat body of the blowfly, Calliphora vicina.

Rates of ecdysone and 20-hydroxyecdysone metabolism were measured by radio-assay in an in vitro system containing fat body isolated from blowfly larvae. The addition of forskolin which is known to stimulate artificially the intracellular adenylate cyclase system led to decreased rates of conversion of ecdysone into 20-hydroxyecdysone (= hormone activation) and of 20-hydroxyecdysone further to other metabolites (= hormone inactivation). The effect of forskolin was dose-dependent and reversible. Extracts prepared from larval brains were also tested. Some of them had the same effect as forskolin. It is concluded that the reactions leading from ecdysone to 20-hydroxyecdysone and further to hormonally inactive ecdysteroids are modulated by the intracellular level of cyclic nucleotides. We propose that a neurohormone is involved in the control of the reactions of the ecdysone metabolism. The observed new principle may contribute to the control of the titer of moulting hormone.