Studies on the Energy Mobilizing Hormones in Insects.

Abstract

Chemical factors controlling the energy mobilization in three species of insects were identified, partially characterized and their role in the process of energy mobilization were studied. High performance liquid chromatographic fractions were isolated from methanolic extracts of the corpora cardiaca (CC) from the honeybee Apis mellifera, the paper wasp Polistes exclamans and the house cricket Acheta domesticus. Each species had a single active fraction that was able to elevate the lipid titer in Acheta. Pyroglutamate aminopeptidase digestion of isolated active fractions indicated that these molecules are all peptides with a terminal pyroglutamate. Methanolic extracts of CC from Apis, Polistes and Acheta elevated the total blood sugar titer in Periplaneta americana and the blood lipid titer in Locusta migratoria. Injections of native CC extracts resulted in an elevation of the trehalose titer in Polistes and an increase in the glucose titer in Apis. The adipokinetic neuropeptide from the CC of Acheta was sequenced and found to be identical to a previously described peptide Gryllus bimaculatus adipokinetic hormone (Grb-AKH). The Grb-AKH content in the CC did not change in the larval or adult stage, but its hyperlipemic effect greatly varied depending on the age of Acheta. Diel rhythms in the Grb-AKH content in the CC, fat body response, and the blood lipid and sugar levels of Acheta were described. There were two distinct peaks of total blood lipid concentration and of fat body response to Grb-AKH in Acheta. AKH increased the rate of fat body lipid secretion, and decreased the rate of fat body lipid synthesis in crickets. An inhibitory effect of Grb-AKH on the fat body protein synthesis in male crickets and on the protein uptake by the ovary in female crickets was also observed. The presence of a heat-labile factor in the mid-gut with a hypolipemic and hypotrehalosemic effect in Acheta was also demonstrated. This factor is probably an insulin-like molecule.