Relative Hypertrehalosaemic Activities of Naturally Occurring Neuropeptides from the AKH/RPCH Family

Abstract

Dose-response curves for the ability to increase blood carbohydrates of the cockroach are compared for various naturally occurring neuropeptides from the corpus cardiacum of different insect species. The peptides investigated are the (decapeptides) locust adipokinetic hormone I (AKH I) and stick insect hypertrehalosaem ic factor II. as well as the (octapeptides) cockroach hypertrehalosaemic horm ones I and II (M I and M II), adipokinetic hormone II from the migratory locust (AKH II-L), and the crustacean red pigment-concentrating hormone (RPCH ). The data show clearly that M I and M II display almost identical dose-response curves with a maximal response at about 5 pmol and ED50 values (the amount of peptide which is needed to produce 50% of the hypertrehalosaemic response) of 1.9 and 1.8 pmol. respectively. The stick insect peptide is remarkably more potent (ED 50 value: 0.9 pmol), but the other decapeptide. AKH I, gives only about a 70% response com pared with M I and M II. as does the octapeptide RPCH. The ED 50 values of those peptides are 5.9 and 4.5 pmol, respectively. Biological activity after injection of AKH II-L, which lacks a proline residue in the molecule, is only measurable at pharmacologically high doses. An attempt is made to relate the observed differences in the doseresponse relationships to the amino acid sequences of the neuropeptides.