ECDYSTEROIDOGENIC ACTION OF BOMBYX PROTHORACICOTROPIC HORMONE AND BOMBYXIN ON THE PROTHORACIC GLANDS OF RHODNIUS-PROLIXUS IN-VITRO

An in vitro assay for ecdysteroid synthesis by the prothoracic glands (PGs) of fifth instar Rhodnius prolixus has been employed to evaluate the actions of prothoracicotropic neuropeptides from the silkmoth, Bom byx mori, Crude prothoracicotropic hormone (PTTH) extracts of recently emerged adult brain complexes of Bombyx induced a dose-dependent stim ulation of ecdysteroid synthesis by Rhodnius PGs, which was similar to that obtained using crude Rhodnius PTTH, In both cases, maximum stimu lation was obtained with one brain equivalent, Rhodnius PGs were then challenged with incremental doses of recombinant Bombyx PTTH and synth etic bombyxin-II. Dose-response curves for the action of both peptides on Rhodnius PGs were very similar to those obtained for their action on the pupal PGs of Bombyx in vitro, Bombyx PTTH stimulated the PGs of Rhodnius at concentrations comparable to those effective on Bombyx. T he curve for Bombyx PTTH showed a steep ascending region from 3 to 8 n g/ml and a sharp peak, For bombyxin, concentrations 40-fold higher wer e required to elicit the same amount of stimulation as obtained using Bombyx PTTH, Therefore, Rhodnius PGs possess recognition sites for bot h Bombyx PTTH and bombyxin, This is the first study of the ecdysteroid ogenic properties of the Bombyx peptides on a heterologous species. It is suggested that the function and conformation of PTTH may be conser ved between distantly related insect groups. (C) 1997 Elsevier Science Ltd.