Identification of a metabolic peptide hormone from the neurohaemal tissues of Orthaga exvinacea

The presence of biologically active compounds in the neuronal tissues of the mango leaf webber, O. exvinacea that can influence lipid, carbohydrate and protein metabolism were investigated. The activity of the brainretrocerebral complex extract tested in vivo in the polyphagous plant bug, Iphita limbata (heterologous bioassay) revealed that the extract and also the synthetic peptide, Locmi-AKH-I can increase both lipid (adipokinetic) and carbohydrate (hyperglycaemic) in the haemolymph whereas they showed inhibitory effects on haemolymph protein content. In vitro studies using fat body taken from O. exvinacea showed similar response of the fat body to the crude extract and the synthetic peptide. The extract was separated by RP-HPLC analysis. Comparison of HPLC profiles of the synthetic peptide with that of the retrocerebral complex extract of O. exvinacea showed that the hormone extract contained materials having similar retention times as that of synthetic AKH. The in vitro bioassays using purified fractions for lipid and carbohydrate mobilization on the fat body showed a prominent hyperlipaemic and hyperglycaemic effects, but significant inhibition were obtained when tested for the protein turnovers. The present study revealed that the peptide hormone extracted is a stimulator of fat body lipid and carbohydrate release, showing an increase in lipid and carbohydrate titers, whereas they are potent inhibitors of protein metabolites.