dynorphins and bremazocine

Evidence from studies which utilise either opiate receptor agonists and antagonists strongly indicate a role for endorphinergic mechanisms in the control of feeding responses. Two means by which these compounds may exert an effect on feeding can be singled-out. Firstly, emerging evidence suggests that the process of achieving satiety (terminating a meal, or choice of a commodity) may be accelerated following treatments with opiate receptor antagonists. Secondly, the preference for highly palatable solutions (sweet solutions have received most attention) in two-bottle tests is blocked after injection of opiate receptor antagonists. This finding has been interpreted in terms of the abolition of the reward or incentive quality associated with the particularly attractive flavour. These two mechanisms of action may represent two aspects of a single, fundamental process. Following an introduction to rat urination model of in vivo kappa agonist activity, the consistent effect of several kappa agonists (including the highly selective U-50,488H) to stimulate food consumption is described. Recognising that members of the dynorphin group of endogenous opioid peptides are kappa receptor ligands, some with a high degree of selectivity, and the evidence the dynorphins and neo-endorphins produce hyperphagia in rats is particularly interesting. Such lines of evidence lead to the hypothesis that peptides of the dynorphin group may act endogenously to promote the expression of normal feeding behaviour.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Benzodiazepines; Benzomorphans; Butorphanol; Choice Behavior; Cyclazocine; Diuresis; Drinking; Dynorphins; Eating; Endorphins; Ethylketocyclazocine; Humans; Morphine; Narcotic Antagonists; Phenazocine; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, kappa; Satiety Response

1. Various neurotransmitters in the brain regulate gastric acid secretion. Previously, we reported that the central injection of kappa-opioid receptor agonists stimulated this secretion in rats. Although the existence of kappa(1)-kappa(3)-opioid receptor subtypes has been proposed, the character is not defined. We investigated the interactions between kappa-opioid receptor subtypes and glutamate, gamma-amino-butyric acid (GABA) or 5-hydroxy tryptamine (5-HT) receptors in the rat brain. 2. Gastric acid secretion induced by the injection of U69593 (8.41 nmol, a putative kappa(1)-opioid receptor agonist) into the lateral cerebroventricle was completely inhibited by the central injection of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10.9 nmol, an antagonist for non-N-methyl-D-aspartate (non-NMDA) receptors) and by bicuculline infusion (222 micro g kg(-1) per 10 min, i.v., GABA(A) receptor antagonist). The secretion induced by bremazocine (8.52 nmol, a putative kappa(2)-opioid receptor agonist) was inhibited by bicuculline infusion, but not by CNQX. The secretion induced by naloxone benzoylhydrazone (224 nmol, a putative kappa(3)-opioid receptor agonist) was slightly and partially inhibited by CNQX and bicuculline. 3. Treatment with CNQX and bicuculline inhibited gastric acid secretion induced by the injection of dynorphin A-(1-17) into the lateral, but not the fourth, cerebroventricle. Antagonists for NMDA, GABA(B) and 5-HT(2/1C) receptors did not inhibit the secretions by kappa-opioid receptor agonists. 4. In rat brain regions close to the lateral cerebroventricle, kappa-opioid receptor systems (kappa(1)>kappa(3)>>kappa(2)) are regulated by the non-NMDA type of glutamate receptor system, and kappa(1)- and kappa(2)-opioid receptor systems are regulated by the GABA(A) receptor system. The present findings show pharmacological evidence for kappa-opioid receptor subtypes that regulate gastric acid secretion in the rat brain.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Benzeneacetamides; Benzomorphans; Bicuculline; Brain; Dynorphins; gamma-Aminobutyric Acid; Gastric Acid; Injections, Intraventricular; Ketanserin; Male; Perfusion; Piperazines; Pyrrolidines; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, kappa; Receptors, Serotonin; Stomach

8-Methyl-N-vanillyl-6-nonenamide (capsaicin) was locally applied in the tail of rhesus monkeys to evoke a nociceptive response, thermal allodynia, which was manifested as reduced tail-withdrawal latencies in normally innocuous 46 degrees C water. Coadministration of three kappa opioid ligands, U50,488 (3.2-100 microgram), bremazocine (0.1-3.2 microgram), and dynorphin A(1-13) (3.2-100 microgram), with capsaicin in the tail dose-dependently inhibited capsaicin-induced allodynia. This local antinociception was antagonized by a small dose of an opioid antagonist, quadazocine; (0.32 mg), applied in the tail; however, this dose of quadazocine injected s.c. in the back did not antagonize local U50,488. Comparing the relative potency of either agonist or antagonist after local and systemic administration confirmed that the site of action of locally applied kappa opioid agonists is in the tail. In addition, local nor-binaltorphimine (0.32 mg) and oxilorphan (0.1-10 microgram) antagonist studies raised the possibility of kappa opioid receptor subtypes in the periphery, which indicated that U50,488 produced local antinociception by acting on kappa1 receptors, but bremazocine acted probably on non-kappa1 receptors. These results provide functional evidence that activation of peripheral kappa opioid receptors can diminish capsaicin-induced allodynia in primates. This experimental pain model is a useful tool for evaluating peripherally antinociceptive actions of kappa agonists without central side effects and suggests new approaches for opioid pain management.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Azocines; Benzomorphans; Capsaicin; Dynorphins; Female; Hot Temperature; Ligands; Macaca mulatta; Male; Naltrexone; Narcotic Antagonists; Pain Measurement; Peptide Fragments; Receptors, Opioid, kappa

1. The kappa 1 and kappa 2 opioid receptor agonists U-62066 (8 mg/kg, i.p.) and (-)-bremazocine (0.7 mg/kg, i.v.), respectively, both exhibit anti-arrhythmic properties against adrenaline-induced dysrhythmias in rats. 2. In contrast, (+)-bremazocine has no effect on adrenaline-induced dysrhythmias. 3. The kappa 1 opioid receptor agonists U-50488 (110 nmol) and [D-Ala2]-dynorphin A (20 nmol) and the kappa 2 opioid receptor agonist (-)-bremazocine (30 nmol) exhibit pro-arrhythmic properties following intracerebroventricular administration. 4. Prior administration of the kappa opioid receptor antagonist nor-binaltorphimine doses i.c.v. (14 nmol), i.p. (10 mg/kg), completely abolishes the pro-arrhythmic (BNI, i.c.v., 14 nmol) as well as anti-arrhythmic (BNI, 10 mg/kg, i.p.) effects of the kappa opioid receptor agonists. 5. Neither hexamethonium (10 mg/kg, i.v.) nor atropine (1 mg/kg, i.v.) have any effect on the anti-arrhythmic actions of the kappa 1 opioid receptor agonist U-62066 following systemic administration. 6. It is suggested that the anti-arrhythmic effects of U-62066 and (-)-bremazocine are associated with the activation of peripheral kappa opioid receptors and do not depend on the activation of kappa opioid receptors in the autonomic nervous system.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Anti-Arrhythmia Agents; Antihypertensive Agents; Arrhythmias, Cardiac; Benzomorphans; Dynorphins; Male; Pyrrolidines; Rats; Rats, Wistar; Receptors, Opioid, kappa

Modulation of depolarization-activated ionic conductances by opioid receptor agonists was investigated in isolated parasympathetic neurons from neonatal rat intracardiac ganglia by using the whole cell perforated patch clamp technique. Met-enkephalin (10 muM) altered the action potential waveform, reducing the maximum amplitude and slowing the rate of rise and repolarization but the afterhyperpolarization was not appreciably altered. Under voltage clamp, 10 muM Met-enkephalin selectively and reversibly inhibited the peak amplitude of high-voltage-activated Ca2+ channel currents elicited at 0 mV by approximately 52% and increased three- to fourfold the time to peak. Met-enkephalin had no effect on the voltage dependence of steady-state inactivation but shifted the voltage dependence of activation to more positive membrane potentials whereby stronger depolarization was required to open Ca2+ channels. Half-maximal inhibition of Ba2+ current (IBa) amplitude was obtained with 270 nM Met-enkephalin or Leu-enkephalin. The opioid receptor subtype selective agonists, DAMGO and DADLE, but not DPDPE, inhibited IBa and were antagonized by the opioid receptor antagonists, naloxone and naltrindole with IC50s of 84 nM and 1 muM, respectively. The kappa-opioid receptor agonists, bremazocine and dynorphin A, did not affect Ca2+ channel current amplitude or kinetics. Taken together, these data suggest that enkephalin-induced inhibition of Ca2+ channels in rat intracardiac neurons is mediated primarily by the mu-opioid receptor type. Addition of Met-enkephalin after exposure to 300 nM omega-conotoxin GVIA, which blocked approximately 75% of the total Ca2+ channel current, failed to cause a further decrease of the residual current. Met-enkephalin inhibited the omega-conotoxin GVIA-sensitive but not the omega-conotoxin-insensitive IBa in rat intracardiac neurons. Dialysis of the cell with a GTP-free intracellular solution or preincubation of the neurons in Pertussis toxin (PTX) abolished the attenuation of IBa by Met-enkephalin, suggesting the involvement of a PTX-sensitive Gprotein in the signal transduction pathway. The activation of mu-opioid receptors and subsequent inhibition of N-type Ca2+ channels in the soma and terminals of postganglionic intracardiac neurons is likely to inhibit the release of ACh and thereby regulate vagal transmission to the mammalian heart.

Topics: Acetylcholine; Animals; Animals, Newborn; Anti-Arrhythmia Agents; Benzomorphans; Calcium; Calcium Channels; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Enkephalins; Heart Conduction System; Ion Channel Gating; Ion Transport; Naloxone; Naltrexone; Narcotic Antagonists; Neurons; omega-Conotoxin GVIA; Parasympathetic Nervous System; Patch-Clamp Techniques; Peptides; Pertussis Toxin; Rats; Receptors, Opioid; Receptors, Opioid, kappa; Virulence Factors, Bordetella

Although only one gene for kappa opioid receptors has been cloned to date, kappa1 and kappa2 receptors have been defined pharmacologically, with drugs such as bremazocine binding to both putative kappa receptor subtypes. To examine whether kappa receptor subtypes can be distinguished at the level of the G-protein, the ability of the kappa1 agonist (trans-(dl)-3,4-dichloro-N- methyl-N-[2-(1 -pyrrolidinyl)cyclohexyl]-benzeneacetamide) methane sulfonate (U-50488H) to stimulate [35S]guanosine-5'-O-(gamma-thio)-triphosphate ([35S]GTPgammaS) binding in guinea pig brain was compared with that of bremazocine and dynorphin. In membranes prepared from guinea pig striatum, both bremazocine and U-50488H stimulated [35S]GTPgammaS binding with the same relative efficacy, while dynorphin produced at least two-fold greater efficacy than the other two agonists. In vitro autoradiography of agonist-stimulated [35S]GTPgammaS binding revealed similar regional distributions of bremazocine- and U-50488H-activated G-proteins. In striatal membranes, the kappa antagonist nor-binaltorphimine (nor-BNI) blocked both bremazocine- and U-50488H-stimulated [35S]GTPgammaS binding with similar Ke values. In agonist additivity experiments, the stimulation of [35S]GTPgammaS binding by the delta agonist [D-pen2'5, p-Cl-Phe4]enkephalin (p-Cl-DPDPE) was approximately additive with the two kappa agonists. Stimulation of [35S]GTPgammaS binding by the mu agonist [D-Ala2, N-Me4, Gly5-ol]-enkephalin (DAMGO) was additive with U-50488H, but not with bremazocine, reflecting the mu antagonist properties of this compound. The combination of bremazocine and U-50488H together produced no greater stimulation of binding than either agonist alone, indicating that they were binding to the same site. These results demonstrate that bremazocine and U-50488H activate G-proteins in guinea pig brain through the same receptor, and suggest that kappa2 receptors are not coupled through the same signal transduction mechanisms as kappa1 receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Autoradiography; Benzomorphans; Brain; Dynorphins; Guanosine 5'-O-(3-Thiotriphosphate); Guinea Pigs; In Vitro Techniques; Male; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Sulfur Radioisotopes

It is unclear how receptor/ligand families that are evolutionarily closely related achieve functional separation. To address this question, we focus here on the newly discovered Orphanin FQ, a peptide homologous to the opioid peptide Dynorphin, and its receptor, the Orphanin FQ receptor, which is highly homologous to the opioid receptors. In spite of this high degree of homology in terms of both ligands and receptors, there is little direct cross-talk between the Orphanin FQ system and the endogenous opioid system. Thus, the opioid peptides show either relatively low affinity or no affinity toward the Orphanin FQ receptor; conversely, Orphanin FQ has no affinity toward any of the opioid receptors. We sought to investigate the molecular basis of such discrimination by attempting to reverse it and endowing the Orphanin FQ receptor with the ability to bind opioids. We report that by mutating as few as four amino acids, we can produce a receptor that recognizes pro-Dynorphin products with very high affinity and yet still binds Orphanin FQ as well as the wild-type receptor. This suggests that the Orphanin FQ receptor has developed features that specifically exclude the opioids and that these features are distinct from those required for the high affinity binding of its own endogenous ligand.

Topics: Analgesics; Animals; Benzomorphans; Dynorphins; Models, Molecular; Naltrexone; Narcotic Antagonists; Nociceptin Receptor; Point Mutation; Rats; Receptors, Opioid

The presence of kappa-opioid receptor subtypes has been clearly established in guinea pig brain. Using [3H]bremazocine in the presence of reversible blockers of mu, delta and kappa 1 receptors, two additional binding sites can be determined in guinea pig brain membranes. The site with higher affinity for the opioid ligands represents kappa 2, while the other site has low affinity and is poorly characterized. The kappa 2 site has high affinity for ethylketocyclazocine and other benzomorphans, as well as for the dynorphin gene products tested. The dynorphin analogs have no appreciable affinity for the low affinity site, so this site should not be called a kappa receptor. With an appropriate membrane preparation, kappa 2 binding can also be demonstrated in the guinea pig ileum. Binding affinities for selected ligands at kappa 2 in guinea pig ileum membranes are very similar to affinities found in brain membranes.

Topics: Analgesics; Animals; Benzomorphans; Brain Chemistry; Dynorphins; Ethylketocyclazocine; Guanylyl Imidodiphosphate; Guinea Pigs; Ileum; In Vitro Techniques; Kinetics; Ligands; Male; Membranes; Myenteric Plexus; Receptors, Opioid, kappa

Previous reports show the tail-flick inhibition induced by bremazocine given i.c.v. is mediated by supraspinal stimulation of both epsilon and kappa opioid receptors and the spinal activation of descending serotonergic and opioid systems. The present studies questioned what endogenous opioid peptides in the spinal cord were involved in i.c.v. bremazocine-induced antinociception in male ICR mice. beta-Endorphin, trans(+-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]- benzene-acetamide methane sulfonate (U50,488H) and morphine were used as reference compounds for epsilon, kappa and mu opioid receptor activity, respectively. Intrathecal pretreatment with antibody to Met-enkephalin dose-dependently attenuated the antinociception induced by i.c.v. bremazocine or beta-endorphin but not morphine or U50,488H; whereas intrathecal (i.t.) pretreatment with antibody to dynorphin A (1-13) dose-dependently blocked the antinociception induced by i.c.v. bremazocine or U50,488H but not beta-endorphin or morphine. Intrathecal Leu-enkephalin and beta-endorphin antibodies did not block i.c.v. bremazocine, beta-endorphin or morphine antinociception. Intrathecal Met-enkephalin or dynorphin A (1-17) increased the tail-flick latency at 1 to 2 min. Met-enkephalin given i.t. blocked the antinociception induced by i.c.v. DPDPE, bremazocine and beta-endorphin but not morphine or U50,488H whereas i.t. dynorphin A (1-17) pretreatment blocked the inhibition induced by i.c.v. U50,488H and bremazocine but not DPDPE, beta-endorphin or morphine. Bremazocine given i.c.v. did not exhibit antianalgesic activity in our studies. The dynorphin released by i.c.v. bremazocine for antinociception appears to be different from the dynorphin released by morphine for antianalgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesia; Animals; Benzomorphans; beta-Endorphin; Drug Interactions; Dynorphins; Enkephalin, Leucine; Enkephalin, Methionine; Injections, Intraventricular; Male; Mice; Mice, Inbred ICR; Morphine; Nociceptors; Pain Measurement; Pyrrolidines; Spinal Cord; Time Factors

The ability of a number of opioid agonists and antagonists to affect nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells has been investigated. High (10 microM) concentrations of the opioid agonist bremazocine produced a significant inhibition of nicotine-induced 45Ca2(+)-uptake throughout the 15 min time course examined. The opioid subtype-selectivity of this inhibition was investigated; mu and delta selective agonists produced only minor effects whereas the kappa selective agonist U50-488H and the endogenous opioid peptides dynorphin(1-13) and metorphamide almost abolished nicotine-induced 45Ca2(+)-uptake. The U50-488H inhibition was significant at 10 nM concentrations with an IC50 of approximately 1 microM. U50-488H inhibition could not be reversed or reduced by the opioid antagonists naxolone, diprenophine or Mr2266. Furthermore, Mr2266 and its optical isomer Mr2267 also produced marked inhibition of 45Ca2(+)-uptake. The inhibition was specific to nicotine-induced 45Ca2(+)-uptake in that a similar level of uptake evoked by potassium depolarization was unaffected by high concentrations of U50-488H. These data indicate that opioid inhibition of nicotine-induced 45Ca2(+)-uptake does not involve classical, stereospecific opioid receptors and suggests the involvement of a pharmacologically distinct opioid recognition site. It is speculated that this may be associated with the nicotine receptor-ionophore complex.

Topics: Adrenal Medulla; Animals; Benzomorphans; Calcium; Cattle; Cells, Cultured; Chromaffin System; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Methionine; Enkephalins; Nicotine; Oligopeptides

Topics: Animals; Benzomorphans; Binding, Competitive; Brain; Dynorphins; Female; Haloperidol; In Vitro Techniques; Mice; Morphinans; Peptide Fragments; Phencyclidine; Piperidines; Receptors, Opioid

Previous studies of kappa opioid binding sites have suggested heterogeneous binding to this class of opioid receptors. To further investigate kappa receptor heterogeneity, we analyzed the binding properties of various "kappa-selective" ligands in rat brain homogenates. Displacement assays were carried out using [3H]bremazocine in the presence of various displacing ligands under mu and delta receptor-blocked conditions. Homologous displacement of [3H]bremazocine produced "shallow" displacement which best fit a two-site model of drug-receptor interaction. Dynorphin A1-13 and U69,593 exhibited similar biphasic displacement of [3H]bremazocine. Maximal displacement by these ligands, however, represented only approximately 55% of total [3H]bremazocine binding, which suggests the existence of a third component of [3H]bremazocine binding. Biphasic displacement by dynorphin A1-13 was detected in tissue throughout the brain and the spinal cord, whereas the dynorphin-resistant component of [3H]bremazocine binding was uniquely absent in the spinal cord. U50,488H, tifluadom and ethylketocyclazocine appeared to displace from additional, dynorphin-insensitive sites, as their maximal displacement exceeded that seen with either dynorphin A1-13 or U69,593. These results strongly suggest the existence of at least three components of non-mu, non-delta [3H]bremazocine binding in the rat brain: two with differential affinity for dynorphin A1-13 and U69-593 (kappa-1 and kappa-2 sites), and a third (termed here R1) that was further resolved into two binding sites by bremazocine. Preliminary analysis of the R1 component using naloxone revealed one high-affinity site, which may be opiate in nature, and a second site whose binding properties closely resemble those of the sigma receptor described by others.

Topics: Analgesics; Animals; Benzeneacetamides; Benzomorphans; Binding, Competitive; Brain; Culture Techniques; Dynorphins; Ligands; Male; Morphinans; Peptide Fragments; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Tritium

The distribution of kappa opioid receptors in guinea pig brain was measured by in vitro receptor autoradiography using [3H]dynorphin A1-9, [3H]dynorphin A1-8 and [3H]bremazocine as ligands. The sites labelled by the two dynorphins had identical, heterogeneous distributions in brain sections. High levels of kappa receptors were seen in striatum, claustrum, nucleus accumbens and laminae V and VI of the cerebral cortex. The substantia nigra and superior colliculus also had high dynorphin binding levels. The [3H]dynorphin autoradiographs were closely similar to those obtained using [3H]bremazocine in the presence of mu and delta receptor displacers. It is concluded that tritiated dynorphin A fragments can be used for autoradiographic studies of kappa opioid receptors in brain.

Topics: Animals; Autoradiography; Benzomorphans; Brain Chemistry; Dynorphins; Guinea Pigs; In Vitro Techniques; Male; Receptors, Opioid; Receptors, Opioid, kappa

The binding of radiolabelled ligands with high affinity for kappa-opioid binding sites has been studied in homogenates of lumbo-sacral spinal cord from the rat. The unselective ligands [3H]bremazocine and [3H]diprenorphine labelled a large number of sites which could not be fully resolved in terms of mu-, delta- and kappa-types by displacement assays. In particular binding at the kappa-site appeared anomalous in that sites which could be identified as high affinity kappa-type represented only 40% of total kappa-binding, defined using the unselective [3H]ligands. This was confirmed by the low levels of binding seen with the kappa-agonists [3H]dynorphin A(1-9) and [3H]U-69593. In guinea-pig cord, under conditions in which binding to mu- and delta-sites was suppressed, [3H]dynorphin A(1-9) and [3H]U-69593 labelled only 60% of the kappa population, defined by the [3H]unselective ligands. The reasons for the observed discrepancies are discussed.

Topics: Animals; Benzeneacetamides; Benzomorphans; Captopril; Diprenorphine; Dynorphins; Guinea Pigs; In Vitro Techniques; Leucine; Ligands; Male; Peptide Fragments; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Spinal Cord

Quantitative autoradiography was used to examine the characteristics of kappa-opiate receptor binding in neural lobe sections from dehydrated rats and water-sated homozygous Brattleboro rats. The density of kappa-sites was decreased by 40% and 44%, respectively, after 5 days of water deprivation or hypertonic saline. Both the density and affinity of kappa-receptor sites were lower in homozygous Brattleboro rats. We suggest that kappa-receptor down-regulation occurs as a result of elevated release of opioid peptides induced by chronic osmotic stimulation.

Topics: Analgesics; Animals; Benzomorphans; Dynorphins; Etorphine; Homeostasis; Kinetics; Male; Pituitary Gland, Posterior; Rats; Rats, Brattleboro; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa

The intrathecal injection of a variety of selective kappa-opioid receptor ligands did not result in significant inhibition of thermal nociceptive tail flick responses in rats. In contrast, these compounds dose dependently inhibited pressure nociceptive responses. Cross-tolerance studies revealed that the kappa-opioid receptor ligands tifluadom, U-50488H and dynorphin-(1-17) act upon a receptor distinguishable from the receptor through which morphine exerts its inhibition of mechanical nociceptive responses. The less selective kappa-opiate receptor ligands bremazocine and ethylketocyclazocine (EKC), however, blocked both tail flick and tail pressure nociceptive responses and their effect showed marked cross-tolerance to morphine in the tail flick nociceptive test, but not for the pressure nociceptive responses. We suggest that EKC and bremazocine act upon the spinal kappa-opioid receptor to block mechanical nociceptive responses but that the analgesic effect of EKC and bremazocine on thermal nociceptive responses is probably mediated via spinal micron- and/or delta-, and delta-opioid receptors, respectively.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Benzodiazepines; Benzomorphans; Cyclazocine; Drug Tolerance; Dynorphins; Ethylketocyclazocine; Injections, Spinal; Male; Morphine; Pyrrolidines; Rats; Rats, Inbred Strains; Reaction Time; Receptors, Opioid; Receptors, Opioid, kappa; Spinal Cord

D-Ala2, D-Leu5-enkephalin (DADLE) and dynorphin1-13 (Dyn1-13) inhibited striatal adenylate cyclase activity, both basal and dopamine-stimulated (DA), in rats and guinea pigs. The kappa-agonists bremazocine (BRZ), U-50,488 (trans-3,4-dicloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide), and U-69,593 (5 alpha, 7 alpha 8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl-1-oxaspiro (4.5)dec-8yl) benzeneacetamide inhibited only the basal adenylate cyclase activity, and such an effect was restricted to guinea pig striatum, an area known to contain a high density of kappa-binding sites. Moreover, BRZ was found to antagonize the inhibitory effect of both DADLE and Dyn1-13 in rat striatum.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Adenylyl Cyclases; Analgesics; Animals; Benzeneacetamides; Benzomorphans; Corpus Striatum; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Guinea Pigs; Male; Morphinans; Peptide Fragments; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid

We investigated the effects of dynorphin A (Dyn A), a heptadecapeptide, on the population spikes of the guinea pig hippocampal CA3 pyramidal neurons, in vitro, using paired-pulse stimulation of the mossy fibers. Dyn A produced facilitatory and inhibitory effects on the population spikes in the preparations with lower and higher degrees of paired-pulse facilitation, respectively. Morphine and D-Ala2, D-Leu5-en-kephalin, mu- and delta-agonist, respectively, predominantly potentiated the population spikes, while kappa-agonists such as U-50, 488H and bremazocine mainly caused an inhibition. These results suggest that Dyn A has two separate (excitatory and inhibitory) effects on the guinea pig hippocampal CA3 neurons through mu-(delta) and kappa-opioid receptors, respectively.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Benzomorphans; Drug Interactions; Dynorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Guinea Pigs; Hippocampus; In Vitro Techniques; Male; Morphine; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu; Synaptic Transmission

Following incubation of [3H]dynorphin A (1-8) and [3H]dynorphin A (1-9) with suspensions of guinea pig brain membranes, analysis of the supernatants by HPLC has shown that both peptides are degraded at 25 degrees C and at 0 degrees C. Bestatin and captopril reduce degradation at 0 degrees C but for a similar degree of protection at 25 degrees C arginine-containing dipeptides are also required. The effects of these peptidase inhibitors on the degradation profiles indicate that [3H]dynorphin A (1-8) has three main sites of cleavage: the Tyr1-Gly2, Arg6-Arg7, and Leu5-Arg6 bonds. With [3H]dynorphin A (1-9) as substrate the Arg7-Ile8 and Ile8-Arg9 bonds are also liable to cleavage. In binding assays, in contrast to the effects of peptidase inhibitors on the degradation of unbound [3H]dynorphin A (1-8) and [3H]dynorphin A (1-9), bestatin and captopril have little effect on the binding characteristics of the tritiated dynorphin A fragments at the kappa-site at 0 degrees C. However, at 25 degrees C binding is low in the absence of peptidase inhibitors. When binding at mu- and delta-sites is prevented, the maximal binding capacities of [3H]dynorphin A (1-8), [3H]dynorphin A (1-9), and [3H](-)-bremazocine at the kappa-site are similar; [3H]dynorphin A (1-9) has 5-10 times higher affinity for the kappa-site than [3H]dynorphin A (1-8). Comparison of the effects of peptidase inhibitors on unbound dynorphin A fragments with their effects in binding assays suggests that the bound peptides are protected from the action of peptidases.

Topics: Animals; Benzomorphans; Binding Sites; Brain; Dynorphins; Guinea Pigs; Kinetics; Membranes; Peptide Fragments; Protease Inhibitors; Receptors, Opioid; Receptors, Opioid, kappa; Substrate Specificity; Temperature

The respiratory and cardiovascular effects of selective kappa opioid agonists were compared following microinjection (0.1 microliter) into the nucleus ambiguus (NA) and the nucleus tractus solitarius (NTS) regions of spontaneously breathing and artificially respired pentobarbital-anesthetized rats. In spontaneously breathing animals, the benzomorphan derivative MRZ 2549 (MRZ, 3 X 10(-11) to 16 X 10(-9) mol) elicited dose-related decreases of mean arterial pressure (MAP), heart rate (HR), and tidal volume (TV) following NA injection; bremazocine (BREM) decreased MAP, HR, and respiratory rate (RR). Following NTS injection, MRZ (3 X 10(-10) to 16 X 10(-9) mol) lowered MAP and TV, the highest dose also lowering HR and RR; BREM (3 X 10(-9) to 16 X 10(-9) mol) decreased MAP and HR. Naloxone (200 micrograms/kg, i.v.) reversed the respiratory effects of MRZ without consistently altering cardiovascular activity. In ventilated animals, NA injections of MRZ or BREM (3 X 10(-9) to 16 X 10(-9) mol) elicited a dose-related decrease of MAP without altering HR. These responses were not reversed by naloxone. The stereoisomer of BREM (+ BREM) was without effect at similar doses (3 X 10(-9) to 16 X 10(-9) mol). MRZ (16 X 10(-9) mol) elicited a naloxone-reversible tachycardia following NTS injection in ventilated animals; no other cardiovascular responses were observed following NTS administration of BREM (16 X 10(-9) mol) or lower doses of MRZ. Dynorphin (1-13) (6 X 10(-9) to 60 X 10(-9) mol) significantly lowered MAP without altering HR following NA microinjections in ventilated animals; the lower dose decreased MAP following NTS injections.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Benzomorphans; Blood Pressure; Dynorphins; Heart; Heart Rate; Male; Medulla Oblongata; Microinjections; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Respiration; Respiration, Artificial; Respiratory Physiological Phenomena; Tidal Volume

3H-Tifluadom labels specifically recognition sites of opioid kappa receptors. Membranes of guinea-pig whole brain bind 3H-tifluadom with two affinities, in contrast to the cerebellum where almost all opioid sites are kappa.

Topics: Animals; Benzodiazepines; Benzomorphans; Binding Sites; Brain; Cyclazocine; Dihydromorphine; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Ethylketocyclazocine; Guinea Pigs; In Vitro Techniques; Male; Morphine; Receptors, Opioid

To determine whether opioid peptide-receptor pharmacological association found in vitro (e.g., enkephalin-delta, dynorphin-kappa) predict anatomical relationships in situ, immunocytochemical and receptor autoradiographic studies were carried out on adjacent sections from the same brains of formaldehyde-perfused rhesus monkeys. Apparent mu and kappa opioid receptors (labeled, respectively, by [3H] naloxone and [3H]bremazocine under different incubation conditions), but not delta opioid receptors (labeled by [3H]D-Ala2, D-Leu5-enkephalin), survived the fixation procedure, and were found to be colocalized throughout the brain. We have observed complex associations between these binding sites and one, two, or all three opioid peptide systems (i.e., proopiomelanocortin, proenkephalin, and prodynorphin) in different brain regions. These multiple opioid peptide-receptor subtype associations are apparent, for example, in neural systems involved in the processing of pain stimuli, and may be important for mediating different types of analgesia. Since differential processing of proenkephalin and prodynorphin can give rise to opioids of varying receptor selectivities, the colocalization of opioid receptor subtypes may signify that such processing is a key regulatory event in determining which receptor subtype is activated and, thus, the physiological consequences of opioid neurotransmission.

Topics: Animals; Benzomorphans; Brain; Brain Mapping; Dynorphins; Endorphins; Enkephalins; Macaca mulatta; Naloxone; Pro-Opiomelanocortin; Radioligand Assay; Receptors, Opioid; Synaptic Transmission

Morphine, bremazocine, dynorphin(1-17) and two of its fragments (1-13) and (1-8) all increased nociceptive pressure thresholds in the rat after intracerebroventricular administration. Morphine also increased nociceptive heat thresholds in the hotplate test at similar dose-levels. In contrast, bremazocine and the dynorphins were totally inactive against the noxious heat stimulus. This profile of antinociceptive activity is typical of kappa receptor agonists.

Topics: Analgesics; Animals; Benzomorphans; Dynorphins; Endorphins; Male; Morphine; Nociceptors; Rats; Rats, Inbred Strains; Structure-Activity Relationship