title: Effects of RH-5992 on ecdysteroidogenesis of the prothoracic glands during the fourth larval instar of the silkworm, Bombyx mori.
abstract: Stage-dependent effects of RH-5992 on ecdysteroidogenesis of the prothoracic glands during the fourth larval instar of the silkworm, Bombyx mori, were studied in the present report. When larvae were treated with RH-5992 during the early stages of the fourth larval instar (between day 0 and day 1), initially ecdysteroid levels in the hemolymph were inhibited. However, 24 h after RH-5992 application, ecdysteroid levels were greatly increased as compared with those treated with acetone. The examination of the in vitro prothoracic gland activity upon RH-5992 application during the early stages of the fourth larval instar confirmed a short-term inhibitory effect. When RH-5992 was applied to the later stages of the fourth larval instar, no effects on both hemolymph ecdysteroid levels and prothoracic gland activity were observed. Addition of RH-5992 to incubation medium strongly inhibited ecdysteroid secretion by the prothoracic glands from the early fourth instar, indicating direct action of RH-5992 on ecdysteroidogenesis by prothoracic glands. Four hours after application with RH-5992 on day 1.5, prothoracic glands still showed an activated response to PTTH in both PTTH-cAMP signaling and the extracellular signal-regulated kinase (ERK) signaling. Moreover, addition of RH-5992 to incubation medium did not interfere with the stimulatory effect of the glands to PTTH in ecdysteroidogenesis. These results indicated that both PTTH-cAMP signaling and PTTH-ERK signaling may not be involved in short-term inhibitory regulation by RH-5992.
authors.affiliation: Department of Zoology, National Museum of Natural Science, Taichung, Taiwan, ROC. gu330@mail.nmns.edu.tw
authors.forename: Shi-Hong
authors.initials: SH
authors.lastname: Gu
authors.forename: Ju-Ling
authors.initials: JL
authors.lastname: Lin
authors.forename: Pei-Ling
authors.initials: PL
authors.lastname: Lin
authors.forename: Rong
authors.initials: R
authors.lastname: Kou
authors.forename: Guy
authors.initials: G
authors.lastname: Smagghe
mesh_terms: D000818:Animals; D012831:Bombyx / Q000187:drug effects* / Q000254:growth & development*; D026461:Ecdysteroids / Q000096:biosynthesis* / Q000097:blood; D006458:Hemolymph / Q000737:chemistry; D006834:Hydrazines / Q000494:pharmacology*; D007301:Insect Hormones / Q000502:physiology; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects / Q000254:growth & development; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D026461:Ecdysteroids; D006834:Hydrazines; D007301:Insect Hormones; D007306:Insecticides; C009089:prothoracicotropic hormone; C082026:tebufenozide