enkephalin--ala(2)-mephe(4)-gly(5)- and tyrosyl-arginyl-phenylalanyl-sarcosine

The involvement of spinal mu-opioid receptor subtypes on the antinociception induced by i.t.-administered Tyr-D-Arg-Phe-sarcosine (TAPS), a N-terminal tetrapeptide analog of dermorphin, was determined in mice tail-flick test. Intrathecal administration of TAPS produced the marked inhibition of the tail-flick response in a dose-dependent manner. The antinociception induced by TAPS was completely eliminated by i.t.-co-administration of Tyr-D-Pro-Phe-Phe-NH2 (D-Pro2-endomorphin-2), the mu1-opioid receptor antagonist, whereas i.t. co-treatment with Tyr-D-Pro-Trp-Phe-NH2 (D-Pro2-endomorphin-1) or Tyr-D-Pro-Trp-Gly-NH2 (D-Pro2-Tyr-W-MIF-1), the mu2-opioid receptor antagonists, did not affect the TAPS-induced antinociception. In contrast, the antinociception induced by i.t.-administered [D-Ala2,N-MePhe4,Gly-ol5]enkephalin was significantly attenuated by i.t.-co-administration of D-Pro2-endomorphin-1 or D-Pro2-Tyr-W-MIF-1, but not D-Pro2-endomorphin-2. These results suggest that TAPS may stimulate spinal mu1-opioid receptors to produce the antinociception.

Topics: Analgesics; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Mice; MSH Release-Inhibiting Hormone; Oligopeptides; Pain Measurement; Protein Isoforms; Receptors, Opioid, mu; Spinal Cord

The antinociceptive effect of Tyr-d-Arg-Phe-Sar (TAPS) at the spinal level was characterized with the mouse tail-flick test. Intrathecal (i.t.) administration of TAPS produced a dose-dependent antinociception. The antinociception induced by TAPS was completely blocked by i.t. pretreatment with the mu-opioid receptor antagonist beta-funaltrexamine, the mu(1)-opioid receptor antagonist naloxonazine or the kappa-opioid receptor antagonist nor-binaltorphimine, but not with the delta-opioid receptor antagonist naltrindole. Moreover, TAPS-induced antinociception was dose-dependently attenuated by i.t. pretreatment with an antiserum against dynorphin B, but not against dynorphin A, alpha-neo-endorphin, [Met(5)]enkephalin, or [Leu(5)]enkephalin. In mice lacking prodynorphin, TAPS-induced antinociception was significantly reduced compared to that in wild-type mice. These results suggest that TAPS mainly stimulates mu(1)-opioid receptors, which subsequently induce the release of dynorphin B, which then acts on kappa-opioid receptors to produce antinociception.

Topics: Analgesics, Opioid; Animals; Dynorphins; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Male; Mice; Mice, Inbred C57BL; Narcotic Antagonists; Nociceptors; Oligopeptides; Receptors, Opioid, mu; Spinal Cord

The dermorphin-derived tetrapeptide Tyr-D-Arg(2)-Phe-Sar(4) (TAPS) was tested for its ability to induce tolerance, cross-tolerance, withdrawal and its substitution properties in rats subjected to chronic intracerebroventricular (i.c.v.) infusions of mu-opiate receptor agonists. Tolerance and cross-tolerance were assessed by quantification of the thermally induced tail-flick response. Chronic intracerebroventricular infusion of TAPS resulted in antinociception at almost 1000-fold lower doses compared to morphine sulphate and [D-Ala(2), MePhe(4)Gly(ol)(5)]enkephalin (DAMGO). Tolerance to the antinociceptive effect of TAPS developed similar to DAMGO and morphine sulphate. Cross-tolerance to intracerebroventricular bolus injections of DAMGO, but not of TAPS, was evident in rats rendered tolerant to morphine sulphate and TAPS. Naloxone-induced withdrawal was equally pronounced in animals treated with morphine sulphate, DAMGO or TAPS. TAPS substituted for morphine sulphate and vice versa regarding the withdrawal syndrome in a cross-over experimental design. In contrast to DAMGO, TAPS retains its antinociceptive effect following bolus administration in rats rendered tolerant to mu-opioid receptor agonists.

Topics: Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Drug Tolerance; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; In Vitro Techniques; Infusion Pumps; Injections, Intraventricular; Male; Morphine; Naloxone; Oligopeptides; Pain; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Substance-Related Disorders; Time Factors

This study was undertaken to examine the receptor selectivity of Met-enkephalin-Arg6-Phe7 (MERF) employing radioreceptor binding assays in human cerebral cortex membranes, and to elucidate the responsible receptors that mediate the regulatory action of MERF on high (20 mM) K+-stimulated release of [3H]norepinephrine ([3H]-NE) in rat cortex slices. Specific binding of [3H]MERF was inhibited by DAMGO, Tyr-D-Arg-Phe-Sar(TAPS), bremazocine and ethylketocyclazocine (EKC), but not by U69,593 (U69) and DPDPE. MERF showed high affinity for specific binding sites of [3H]DAMGO. However, MERF had little influence on the specific binding of [3H]DPDPE, [3H]U69 and [3H]diprenorphine ([3H]DIP) in the presence of 1 microM each of DAMGO, DPDPE and U69. In [3H]NE release experiments using rat cortex slices, DAMGO, MERF and EKC, in order of their potency, inhibited K+-stimulated release of [3H]NE. The inhibitory effects of MERF and DAMGO were more sensitive than that of EKC to antagonism by CTAP, nor-binaltorphimine (nor-BNI) and naloxone. These results suggested that MERF possesses high affinity for mu-receptors, but not for delta-, kappa1-, and very low affinity for kappa2-receptors in human cerebral cortex membranes. Also, the inhibitory effect of MERF on the K+-stimulated release of [3H]NE appears to be mediated by mu-receptors in rat cerebral cortex slices.

Topics: Adult; Animals; Benzeneacetamides; Benzomorphans; Binding Sites; Cerebral Cortex; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Methionine; Ethylketocyclazocine; Female; Humans; Male; Naloxone; Naltrexone; Norepinephrine; Oligopeptides; Peptide Fragments; Peptides; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Somatostatin

The regulation of adenylyl cyclase by opioid receptor types was characterized in the rat nucleus accumbens, a brain region that is involved in the reinforcing effects of drugs of abuse, and in the caudate putamen, a region not implicated in drug reinforcement. Both mu and delta opioid ligands inhibited adenylyl cyclase activity in the nucleus accumbens and in the caudate putamen of rat, whereas the kappa agonist, U69,593 (5 alpha, 7 alpha, 8 alpha)-(+)-N-methyl-N-[7-(pyrrolidinyl)-1-oxaspiro [4,5]dec-8-yl]-benzeneacetamide, was ineffective. The mu agonists, DAMGO and Tyr-D-Arg-Phe-Sar, were more potent inhibitors of the enzyme in caudate putamen than in nucleus accumbens. The delta-selective agonists, DSLET and [D-Ala2]-deltorphin II more potently inhibited adenylyl cyclase in nucleus accumbens than in caudate putamen. Inhibition of the enzyme by DAMGO and Tyr-D-Arg-Phe-Sar was antagonized by the mu-selective competitive antagonist, CTOP D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2, and the noncompetitive mu antagonists, beta-funaltrexamine and naloxonazine. Inhibition of adenylyl cyclase activity by the delta-selective ligands, DPDPE, DSLET and [D-Ala2]-deltorphin II was unaffected by these antagonists. Conversely, the delta-selective antagonists, ICI 174,864 N-allyl2-Tyr-(alpha-aminisobutyric acid)2-Phe-Leu-OH and naltrindole, blocked the effects of the delta but not the mu opioid ligands. Adenylyl cyclase activity in nucleus accumbens and in caudate putamen is subject to regulation by both mu and delta opioid receptors.

Topics: Adenylyl Cyclases; Amino Acid Sequence; Animals; Benzeneacetamides; Caudate Nucleus; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalins; Male; Molecular Sequence Data; Naloxone; Naltrexone; Nucleus Accumbens; Oligopeptides; Putamen; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, mu; Signal Transduction; Somatostatin