A methanolic extract of 7000 desert locust (Schistocerca gregaria) brains contains several factors that stimulate the in vitro release of adipokinetic hormone (AKH) by glandular cells of locust (Locusta migratoria and Schistocerca gregaria) corpora cardiaca. The most potent one has now been fully identified. Matrix-assisted laser desorption ionization mass spectrometry-time of flight analysis revealed a mass of 954.6 Da. The primary structure of the peptide, Pro-Phe-Cys-Asn-Ala-Phe-Thr-Gly-Cys-NH2, appeared identical to that of a previously identified crustacean cardioactive peptide. This myotropin was first isolated from the shore crab, Carcinus maenas, and later from several insect species, but was never reported in the context of AKH release. The present study shows that synthetic crustacean cardioactive peptide induces the release of AKH from corpora cardiaca in a dose-dependent manner when tested in concentrations ranging from 10(-5)-10(-9) M. This is the first demonstration in invertebrates of a peptide neurohormone controlling the release of a second peptide hormone.