In vitro study of the action of adipokinetic hormone in locusts.

The in vitro study was performed in order to demonstrate the structural changes of lipophorin induced in vivo by the injection of adipokinetic hormone (AKH) into adult locusts. After many unsuccessful attempts, we have established the reconstructed incubation system in which purified lipophorin and apolipophorin-III (9 mol/mol lipophorin) are incubated with the fat body in the presence of AKH under a supply of excess oxygen. In this system, high density lipophorin (HDLp) originally present in the incubation medium can be transformed entirely into low density lipophorin (LDLp) due to the loading of an increased amount of diacylglycerol from the fat body. The LDLp formed in this incubation system was exactly the same as the LDLp formed in vivo by the injection of AKH, in terms of density, particle size, diacylglycerol content, and the association with apolipophorin-III (apoLp-III). In the absence of apoLp-III, AKH did not exhibit its function to any extent. It was also demonstrated that the transformation of HDLp to LDLp requires calcium ions. Moreover, it appears that, up to a certain limit, the increase of diacylglycerol content of lipophorin and the amount of apoLp-III associated with lipophorin is nearly proportional to the amount of apoLp-III added to the incubation medium.