Assessment of endogenous enkephalins efficacy in the hot plate test in mice: comparative study with morphine. 1995

F Noble, and B P Roques
Département de Pharmacochimie Moléculaire et Structurale, U266 INSERM--URA D1500 CNRS, Université René Descartes, UFR des Sciences Pharmaceutiques et Biologiques, Paris, France.

The in vivo spare receptor population and the relative efficacies of morphine and the endogenous enkephalins to alleviate thermal nociceptive inputs were compared by using the mu irreversible antagonist beta-funaltrexamine (beta-FNA). Twenty-four hours after i.c.v. administration of beta-FNA at increasing concentrations (0.005-2.5 micrograms), parallel rightward shifts of both morphine and RB 101 (mixed enkephalin-degrading-enzyme inhibitor) dose-response curves, were observed, but the concentration of beta-FNA required to reduce the analgesic responses was about 10 times higher for RB 101 (0.1 microgram) than for morphine (0.01 microgram). The preferential involvement of mu receptors in the analgesic responses obtained after beta-FNA pretreatment, was supported by the inability of the delta-selective antagonist naltrindole to block these effects. In conclusion, it seems that to elicit the same antinociceptive responses, enkephalins could occupy a smaller proportion of mu opioid receptors than morphine, suggesting that the endogenous peptides have a higher efficacy.

UI MeSH Term Description Entries
D008297 Male Males
D009020 Morphine The principal alkaloid in opium and the prototype opiate analgesic and narcotic. Morphine has widespread effects in the central nervous system and on smooth muscle. Morphine Sulfate,Duramorph,MS Contin,Morphia,Morphine Chloride,Morphine Sulfate (2:1), Anhydrous,Morphine Sulfate (2:1), Pentahydrate,Oramorph SR,SDZ 202-250,SDZ202-250,Chloride, Morphine,Contin, MS,SDZ 202 250,SDZ 202250,SDZ202 250,SDZ202250,Sulfate, Morphine
D009270 Naloxone A specific opiate antagonist that has no agonist activity. It is a competitive antagonist at mu, delta, and kappa opioid receptors. MRZ 2593-Br,MRZ-2593,Nalone,Naloxon Curamed,Naloxon-Ratiopharm,Naloxone Abello,Naloxone Hydrobromide,Naloxone Hydrochloride,Naloxone Hydrochloride Dihydride,Naloxone Hydrochloride, (5 beta,9 alpha,13 alpha,14 alpha)-Isomer,Naloxone, (5 beta,9 alpha,13 alpha,14 alpha)-Isomer,Narcan,Narcanti,Abello, Naloxone,Curamed, Naloxon,Dihydride, Naloxone Hydrochloride,Hydrobromide, Naloxone,Hydrochloride Dihydride, Naloxone,Hydrochloride, Naloxone,MRZ 2593,MRZ 2593 Br,MRZ 2593Br,MRZ2593,Naloxon Ratiopharm
D009271 Naltrexone Derivative of noroxymorphone that is the N-cyclopropylmethyl congener of NALOXONE. It is a narcotic antagonist that is effective orally, longer lasting and more potent than naloxone, and has been proposed for the treatment of heroin addiction. The FDA has approved naltrexone for the treatment of alcohol dependence. Antaxone,Celupan,EN-1639A,Nalorex,Naltrexone Hydrochloride,Nemexin,ReVia,Trexan,EN 1639A,EN1639A
D009292 Narcotic Antagonists Agents inhibiting the effect of narcotics on the central nervous system. Competitive Opioid Antagonist,Narcotic Antagonist,Opioid Antagonist,Opioid Antagonists,Opioid Receptor Antagonist,Opioid Reversal Agent,Competitive Opioid Antagonists,Opioid Receptor Antagonists,Opioid Reversal Agents,Agent, Opioid Reversal,Agents, Opioid Reversal,Antagonist, Competitive Opioid,Antagonist, Narcotic,Antagonist, Opioid,Antagonist, Opioid Receptor,Antagonists, Competitive Opioid,Antagonists, Narcotic,Antagonists, Opioid,Antagonists, Opioid Receptor,Opioid Antagonist, Competitive,Opioid Antagonists, Competitive,Receptor Antagonist, Opioid,Receptor Antagonists, Opioid,Reversal Agent, Opioid,Reversal Agents, Opioid
D009619 Nociceptors Peripheral AFFERENT NEURONS which are sensitive to injuries or pain, usually caused by extreme thermal exposures, mechanical forces, or other noxious stimuli. Their cell bodies reside in the DORSAL ROOT GANGLIA. Their peripheral terminals (NERVE ENDINGS) innervate target tissues and transduce noxious stimuli via axons to the CENTRAL NERVOUS SYSTEM. Pain Receptors,Receptors, Pain,Nociceptive Neurons,Neuron, Nociceptive,Neurons, Nociceptive,Nociceptive Neuron,Nociceptor,Pain Receptor
D004305 Dose-Response Relationship, Drug The relationship between the dose of an administered drug and the response of the organism to the drug. Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D004745 Enkephalins One of the three major families of endogenous opioid peptides. The enkephalins are pentapeptides that are widespread in the central and peripheral nervous systems and in the adrenal medulla. Enkephalin
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D017450 Receptors, Opioid, mu A class of opioid receptors recognized by its pharmacological profile. Mu opioid receptors bind, in decreasing order of affinity, endorphins, dynorphins, met-enkephalin, and leu-enkephalin. They have also been shown to be molecular receptors for morphine. Morphine Receptors,Opioid Receptors, mu,Receptors, Morphine,Receptors, mu,Receptors, mu Opioid,mu Receptors,Morphine Receptor,mu Opioid Receptor,mu Receptor,Opioid Receptor, mu,Receptor, Morphine,Receptor, mu,Receptor, mu Opioid,mu Opioid Receptors

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