Adrenocorticotrophic hormone fragments mimic the effect of morphine in vitro

1 Fragments of the N terminal part of adrenocorticotrophic hormone (ACTH) inhibited the electrically evoked contractions of the mouse vas deferens. This inhibition could be antagonized by naloxone. 2 The same fragments displaced radiolabelled morphine from morphine antiserum. 3 Structure-activity relationship studies showed that in both assay systems the active core is located within the sequence ACTH 7--10. 4 It is postulated that the Trp9 residue and the peptide bond between Trp9 and Gly10 are particularly important for interaction of ACTH fragments with morphine receptors.