title: Stimulation of ecdysteroidogenesis by small prothoracicotropic hormone: role of calcium.
abstract: Insect prothoracic glands are regulated by neuropeptide prothoracicotropic hormones (PTTH). In Manduca sexta PTTH exists as two size variants, big PTTH (approximately 25.5 kDa) and small PTTH (approximately 7 kDa). Previous studies indicate that both size variants employ cAMP as a second messenger and that stimulation of ecdysteroid secretion by big PTTH is Ca(2+)-dependent. In the present study, experiments were performed to assess the role of Ca2+ in small PTTH-stimulated ecdysteroid secretion by prothoracic glands from fifth instar larvae. Basal ecdysteroid secretion was not affected by Ca2+ channel blockers (verapamil or lanthanum) or by omission of Ca2+ from the incubation medium. Treatment of glands with a Ca2+ ionophore (A23187 or ionomycin) produced a concentration-dependent stimulation of ecdysteroid secretion. Stimulation of ecdysteroid secretion by small PTTH was suppressed (1) by Ca2+ channel blockers and (2) in Ca(2+)-free medium. A cAMP analog (Sp-cAMPS) stimulated ecdysteroid secretion in the presence of a Ca2+ channel blocker (verapamil) and in Ca(2+)-free incubation medium, and ionophore-induced ecdysteroid secretion appeared to be suppressed by a cAMP antagonist (Rp-cAMPS). The combined results indicate that basal ecdysteroid secretion is not dependent on external Ca2+, and suggest that small PTTH-stimulated ecdysteroid secretion is mediated by an influx of Ca2+ that precedes cAMP formation.
authors.affiliation: Department of Biology, University of Alabama at Birmingham 35294, USA.
authors.forename: G C
authors.initials: GC
authors.lastname: Hayes
authors.forename: D P
authors.initials: DP
authors.lastname: Muehleisen
authors.forename: W E
authors.initials: WE
authors.lastname: Bollenbacher
authors.forename: R D
authors.initials: RD
authors.lastname: Watson
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D026461:Ecdysteroids; D004702:Endocrine Glands / Q000187:drug effects / Q000378:metabolism; D007301:Insect Hormones / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D018402:Manduca / Q000187:drug effects / Q000378:metabolism; D009479:Neuropeptides / Q000494:pharmacology*; D013256:Steroids / Q000096:biosynthesis*
chemical_list: D026461:Ecdysteroids; D007301:Insect Hormones; D007476:Ionophores; D009479:Neuropeptides; D013256:Steroids; D000001:Calcimycin; C009089:prothoracicotropic hormone; D000242:Cyclic AMP; D002118:Calcium