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Clinical pharmacology: opioids
Published in Pamela E Macintyre, Suellen M Walker, David J Rowbotham, Clinical Pain Management, 2008
David J Rowbotham, Alcira Serrano-Gomez, Anne Heffernan
Attempts to clone the known opioid receptors led to the accidental cloning of a new, previously unidentified opioid-like receptor. This was christened the orphan receptor because no ligand was known at that time.43 However, a year later, the endogenous ligand was discovered simultaneously by two groups, who named the agonist orphanin F/Q (owing to its terminal amino acids) or nociceptin.45, 46 Nociceptin/orphanin FQ (N/OFQ) is a heptadecapeptide cleaved from prepronociceptin and shows similarity to dynorphin A.47 The “orphan” receptor has been given numerous names: ORL-1 (opioid receptor like), NCR (nociceptin receptor), or OP4. However, latest guidelines from IUPHAR recommend that, because of the structural relationship between this receptor and μ, κ, and δ receptors, it should be considered as a nonopioid branch of the opioid family of receptors. They propose the abbreviation NOP for this receptor.48
The potential interplay between opioid and the toll-like receptor 4 (TLR-4)
Published in Immunopharmacology and Immunotoxicology, 2023
Nasrin Zare, Marjan Pourhadi, Golnaz Vaseghi, Shaghayegh Haghjooy Javanmard
Opioids are classified base on the type of opioid receptors. These receptors are located on neuronal cell membranes and all the receptors (the delta receptor or DOP, the kappa receptor or KOP, the mu receptor or MOP, and nociceptin receptor or NOP) are a member of the large family of G-protein-coupled receptors. Pharmacological investigations demonstrate that enkephalins interact with delta receptors or DOP, dynorphin with k receptors or KOP and β-endorphin and endomorphin 1 and 2 with m receptors or MOP and nociceptin receptor or NOP with nociceptin/orphanin FQ (N/OFQ). As well, most clinical drugs such as morphine (a potent alkaloid in opium), Fentanyl/remifentanil, buprenorphine, codeine, and methadone bind to MOP receptors. Furthermore, the opioid antagonist (naloxone and naltrexone) could inhibit all opioid receptors; however, they have the most affinity for m receptors [3–6].
Neuropharmacological basis for multimodal analgesia in chronic pain
Published in Postgraduate Medicine, 2022
Ryan Patel, Anthony H Dickenson
The pain-relieving properties of naturally occurring opioids have been utilized for centuries, and today opioids remain the mainstay of treating acute and chronic pain. Morphine has become the gold standard analgesic to which all others are compared. The classical opioid receptors μ, δ and κ are G-protein coupled, and later a fourth opioid-like receptor (ORL1) was described and renamed the nociceptin receptor. Soon after, a series of endogenous peptide ligands were described. Most of these bind to multiple receptors through endomorphin-1/2 and β-endorphin have highest affinity for μ-opioid receptors, met- and leu-enkephalin have highest affinity δ-opioid receptors, dynorphin A/B have highest affinity κ-opioid receptors, and nociceptin/orphanin FQ has highest affinity for the nociceptin receptor [69]. Upon receptor activation neuronal excitability or action potential propagation is inhibited by several mechanisms including opening of G protein–coupled inwardly rectifying potassium channels [70], inhibition of sodium [71] and calcium channels [72], and inhibition of Ih currents [73].