Analgesic potency of TRIMU-5: a mixed mu 2 opioid receptor agonist/mu 1 opioid receptor antagonist.
TRIMU-5 (Tyr-D-Ala-Gly-NH-(CH2)2CH(CH3)2) is a potent enkephalin analog with analgesic actions. Detailed studies show high affinity for both mu 1 and mu 2 sites, with poor affinity for delta, kappa 1 and kappa 3 receptors. Of all the mu ligands examined in binding assays, TRIMU-5 was the most mu-selective. In mice, TRIMU-5 administered either intracerebroventricularly (i.c.v.) or intrathecally elicited analgesia which was readily reversed by the mu-selective antagonist beta-funaltrexamine (beta-FNA). However, the analgesia observed following i.c.v. injections differed from traditional mu ligands: (1) the dose of drug required for analgesic activity i.c.v. was 100-fold greater than those following intrathecal administration; (2) although sensitive to beta-FNA, the analgesia was not antagonized by naloxonazine; and (3) the analgesia was reversed by an opioid antagonist given intrathecally (i.t.) but not i.c.v. Thus, TRIMU-5 analgesia appeared to be mediated spinally through mu 2 receptors. TRIMU-5 did have supraspinal actions, inhibiting gastrointestinal transit, another mu 2 action. In binding studies TRIMU-5 had high affinity for mu 1 sites, but pharmacological studies revealed antagonist actions at this receptor. In mice, the analgesia produced by morphine given i.c.v. was antagonized by coinjection of a low TRIMU-5 dose which was inactive alone. Similarly, TRIMU-5 coadministered with morphine into the periaqueductal gray of rats reversed the analgesia seen with morphine alone. Thus, TRIMU-5 is a highly selective mixed mu 2 opioid receptor agonist/mu 1 opioid receptor antagonist.
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Cotzias Laboratory of Neuro-Oncology, Memorial Sloan-Kettering Cancer Center, New York 10021.
Pick
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Paul
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Roques
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Gacel
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Pasternak
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D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005772:Gastrointestinal Transit / Q000187:drug effects; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000145:classification / Q000187:drug effects*
D000700:Analgesics; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; D009020:Morphine; C076955:TRIMU 5