In vitro studies on hormone-stimulated lipid mobilization from fat body and interconversion of haemolymph lipoproteins of Locusta migratoria

Abstract

Both adipokinetic hormone and octopamine have a stimulating effect on lipid release from locust fat body in vitro, when incubated in diluted haemolymph. The presence of adipokinetic hormone results in the formation of the flight-specific haemolymph lipoprotein A⁺ accepting the increased amount of lipids released into the incubation medium. In contrast, interconversions of lipoproteins do not occur when octopamine is added to the incubation medium, which is in line with the expectations: the lipidmobilizing effect of octopamine is a limited and short-term effect. When fat body tissue is incubated with isolated haemolymph protein fractions, the lipid-mobilizing effect of adipokinetic hormone only occurs when the incubation medium contains both lipoprotein Ay and protein fraction C, resulting in the formation of lipoprotein A⁺. In similar control incubations with the hormone omitted, some lipoprotein A⁺ is also formed (concomitant with a slight amount of lipid released), though significantly less than in incubations with hormone. Besides a stimulating function on lipolytic processes in the fat body, adipokinetic hormone is suggested to influence haemolymph lipoprotein rearrangement. A possible counteracting function of another factor in the haemolymph is discussed.