TREHALOSE INHIBITS THE RELEASE OF ADIPOKINETIC HORMONES FROM THE CORPUS CARDIACUM IN THE AFRICAN MIGRATORY LOCUST, LOCUSTA-MIGRATORIA, AT THE LEVEL OF THE ADIPOKINETIC CELLS

The effect of trehalose at various concentrations on the release of ad ipokinetic hormones (AKHs) from the adipokinetic cells in the glandula r part of the corpus cardiacum of Locusta migratoria was studied in vi tro. Pools of five corpora cardiaca or pools of five glandular parts o f corpora cardiaca were incubated in a medium containing different con centrations of trehalose in the absence or presence of AKH-release-ind ucing agents. It was demonstrated that trehalose inhibits spontaneous release of AKH I in a dose-dependent manner. At a concentration of 80 mM, which is the concentration found in the hemolymph at rest, trehalo se significantly decreased the release of AKH I induced by 100 mu M lo custatachykinin I, 10 mu M 3-isobutyl-1-methylxanthine (IBMX) or high potassium concentrations. The specificity of the effect of trehalose w as studied by incubating pools of corpora cardiaca with the non-hydrol yzable disaccharide sucrose or with glucose, the degradation product o f trehalose, both in the presence and absence of 10 mu M IBMX. Sucrose had no effect at all on the release of AKH I, whereas glucose strongl y inhibited its release. The results point to the inhibitory effect of trehalose on the release of AKH I being exerted, at least partly, at the level of the adipokinetic cells, possibly after its conversion int o glucose. The data presented in this study support the hypothesis tha t in vivo the relatively high concentration of trehalose (80 mM) at re st strongly inhibits the release of AKHs. At tile onset of flight, the demand for energy substrates exceeds the amount of trehalose that can be mobilized from the fat body and consequently the trehalose concent ration in the hemolymph decreases. This relieves the inhibitory effect of trehalose on the release of AKHs, which in turn mobilize lipids fr om the fat body.