Central antldiarrheal and colonlc antiprofulsive effects of D-ala-deltorphin II, a selective delta opioid agonist, in the mouse

Abstract

The deltorphins are a class of highly selective δ-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring d-enantiomer at the second position in their common N-terminal sequence, Tyr–d-Xaa–Phe, comparable to dermorphin, which is the prototype of a group of μ-selective opioids from the same source. The d-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high δ-receptor affinity, bioactivity and peptide conformation.This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the δ-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure–activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the δ-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand–receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.