Invertebrate neuropeptide hormones

The development of a long-term research program on the neurosecretory hormones of arthropods is described. The purification and full characterization of the first invertebrate neurohormones, the red pigment-concentrating hormone (RPCH) and the distal retinal pigment hormone (DRPH) demonstrated that they are peptides, an octapeptide and an octadecapeptide, respectively. Physiological function studies with the pure hormones and their synthetic preparations showed that the RPCH acts as a general pigment-concentrating hormone (PCH), and that the DRPH, in addition to its light-adaptive function, also constitutes a general pigment-dispersing hormone (PDH). In the regulation of the color-adaptation of the animals, the two hormones act as antagonists. The chromatophorotropic activities are widely distributed within the arthropod neuroendocrine systems. Purification of the pigment-concentrating activities from the locust corpora cardiaca lead to the isolation and characterization of the first insect neurohormones, the adipokinetic hormones (AKH I and AKH II). These two hormones, AKH I being a decapeptide and AKH II being an octapeptide, are close structural analogs to the crustacean PCH, demonstrating a common evolution of arthropod neurohormones. The hormones of this PCH-family all cross-react, but structure-function studies of the hormones show that quite different parts of their structure are involved in their binding to the various receptors.