Juvenile hormone synthesis in vitro by larval and pupal corpora allata of Manduca sexta.

The synthesis of juvenile hormone I (JH I) and juvenile hormone III (JH III) in vitro by isolated corpora allata (CA) and brain-corpora cardiaca-corpora allata complexes (BR-CC-CA) from fourth and fifth instar larvae and pupae of Manduca sexta was assessed by JH I and JH III radioimmunoassays of incubation medium. Fluctuations in synthesis occurred at specific stages during larval-pupal development. These fluctuations temporally approximated those of previously determined hemolymph titers of JH I and III for this developmental period, except for the synthesis of JH III during the prepupal period, when the JH III hemolymph titer was negligible but JH III synthesis in vitro increased to the highest rate observed. The overall agreement between CA activity and the JH hemolymph titers suggests that the in vitro system supports physiological gland activity and that changes in biosynthesis contribute significantly to changes in the titers. A comparison of JH I and JH III synthesis by isolated CA with that by BR-CC-CA suggests that the BR-CC can differentially modulate the synthesis of these two homologs. The significance of these findings with regard to the possible endocrine function of JH III and the proposed neuroendocrine control of the CA is discussed.