Comparison of the inhibitory effects of brain extract,high K+ and forskolin on juvenile hormone synthesis by Diploptera punctata corpora allata

We compared the effects of three treatments (brain extracts, high K⁺, forskolin) which inhibit JH synthesis by corpora allata of the cockroach Diploptera punctata incubated in vitro. Corpora allata showed a similar developmental sensitivity to all three treatments, with a high level of inhibition in glands of low activity. Inhibition of JH III synthesis by forskolin, high K⁺ or brain extract was antagonized by mevalonate and farnesoic acid, thus implicating an early biosynthetic step as the target of inhibition. All three treatments were also antagonized by Mn²⁺, suggesting that the inhibitory mode of action may be dependent upon Ca²⁺. Inhibition for forskolin and by high K⁺ was not only reversible, but caused a stimulation of JH synthesis upon removal of the inhibitor, suggesting that more than one regulatory mechanism is affected by these treatments.