A kinetics analysis of brain-mediated 20-hydroxyecdysone stimulation of the corpora allata of Manduca sexta.

An in vitro method for investigating 20-hydroxyecdysone regulation of the corpora allata (CA) has been used to assess the kinetics of stimulation of precommitment day 3 fifth (V) larval instar Manduca sexta CA by 20-hydroxyecdysone. The synthesis of juvenile hormone (JH) I and III acids by 20-hydroxyecdysone-stimulated CA incubated as complexes with the brain-corpora cardiaca (Br-CC) increased similarly over time; the synthesis of JH III acid was greater than that of JH I acid. Maximal stimulation of the CA to synthesize both JH acids occurred when the Br-CC-CA were exposed to 20-hydroxyecdysone for 30-60 min. Following stimulation, the elevated rates of JH I and JH III acid synthesis remained unchanged over an 11 h incubation in the absence of the steroid hormone, suggesting that once stimulated by 20-hydroxyecdysone the CA biosynthetic response is persistent. These kinetics data provide insight into the means by which 20-hydroxyecdysone stimulates the CA via the Br-CC.