Developmental profile of the changes in the prothoracicotropic hormone titer in hemolymph of the silkworm Bombyx mori: correlation with ecdysteroid secretion

A very sensitive time-resolved fluoroimmunoassay for the prothoracicotropic hormone (PTTH) of the silkworm Bombyx mori has been established. The lower limit of detection in this assay was 0.1 pg. With this assay method, the a mounts of PTTH in the central nervous system and hemolymph were quantified. PTTH was detected only in the brain within the central nervous system, and , in the fifth instar, its content in the brain increased gradually with la rval growth and decreased rapidly after the beginning of wandering. A subst antial amount of PTTH was also found in the retrocerebral complex of day-3 fifth instar larvae, accounting for 28% of total PTTH. The PTTH titer in he molymph changed dramatically during Bombyx development, with a small peak i n the middle of the fourth instar, medium-sized peaks at the wandering and prepupal stages in the fifth instar, and a large prolonged peak during earl y pupal-adult development. The changes were overall closely correlated with those in hemolymph ecdysteroid titer. However, some unexpected aspects of PTTH dynamics in hemolymph have also been disclosed. Based on these observa tions, the significance of PTTH secretion in the control of insect developm ent is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.