Opioid activity of dermenkephalin analogues in the guinea-pig myenteric plexus and the hamster vas deferens.
1. To elucidate the structural features required for selective and potent action of dermenkephalin at the delta-opioid receptor, a series of analogues of dermenkephalin and dermorphin were tested for their effectiveness in depressing electrically-evoked contractions of the vas deferens of the hamster (delta-opioid receptors) and the guinea-pig myenteric plexus-longitudinal muscle preparation (mu- and kappa-opioid receptors). 2. Dermenkephalin was more selective and more potent at delta-receptors than the delta-ligand [D-Pen2, D-Pen5]-enkephalin. The responses to dermenkephalin in the hamster vas deferens were increased by addition of peptidase inhibitors; the maximum effect was obtained with 3 microM thiorphan. 3. [L-Met2]-dermenkephalin had 0.2% and [L-Ala2]-dermorphin 0.01% of the agonist activity of the corresponding endogenous peptides which have D-amino acids in position 2. The pharmacological activity of these analogues was unaffected by inhibition of peptidases. This emphasizes the role that the D-configuration plays in determining the bioactive folding of these highly active peptides. 4. Dermenkephalin-(1-6)-NH2 was more potent at delta-receptors than at mu-receptors whereas, dermenkephalin-(1-4)-NH2 is a selective mu-agonist, having no activity at delta-receptors. 5. Substitution of the C-terminal tripeptide of dermorphin with the C-terminal tripeptide of dermenkephalin abolished the mu-receptor preference of dermorphin. The resulting hybrid peptide, Tyr-D-Ala-Phe-Gly-Leu-Met-Asp-NH2 was as potent as dermenkephalin at delta-receptors. A shift towards a preference for delta-receptors was obtained when the C-terminal tetrapeptide of dermorphin was replaced by the C-terminal tetrapeptide of dermenkephalin. 6. Substitution of Asp by Asn in position 7 of dermenkephalin caused an increase in mu-receptor potency and a decrease in delta-receptor potency, resulting in a 20 fold decrease in mu-receptor selectivity. Dermenkephalin-(1-6)-NH2 and [Asn7]-dermenkephalin have almost identical delta-receptor agonist potencies and ratios of IC50 in the myenteric plexus to IC50 in the hamster vas deferens. 7. The results obtained emphasise the importance of a negative charge at the C-terminus of dermenkephalin for selectivity at the delta-opioid receptor. Furthermore, the hydrophobic residues Leu5 and Met6 may be critical in ensuring tight binding to the receptor which results in high agonist potency.
Sagan
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S
Laboratoire de Bioactivation des Peptides, Institut Jacques Monod, Université Paris 7, France.
Corbett
A D
AD
Amiche
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M
Delfour
A
A
Nicolas
P
P
Kosterlitz
H W
HW
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001681:Biological Assay; D006224:Cricetinae; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D051379:Mice; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000187:drug effects*; D009197:Myenteric Plexus / Q000187:drug effects; D009842:Oligopeptides / Q000494:pharmacology*; D018847:Opioid Peptides; D010455:Peptides / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D011487:Protein Conformation; D011957:Receptors, Opioid / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects
D000596:Amino Acids; D009842:Oligopeptides; D018847:Opioid Peptides; D010455:Peptides; D011480:Protease Inhibitors; D011957:Receptors, Opioid; C059567:deltorphin; C030058:dermorphin