morphinans and cyprodime

Bone resorption associated to chronic diseases, such as arthritis and periodontitis, results from exacerbated immuno-inflammatory host response that leads to tissue breakdown. The significance of opioid pathways as endogenous modulators of inflammatory events has already been described. Thus, the aim of this work is to determine whether some of the main three opioid receptors are endogenously activated to prevent bone loss during experimentally-induced alveolar bone resorption.. This study used an experimental model of alveolar bone resorption induced by ligature in rats. A silk thread was placed around the 2nd maxillary molar of male Wistar rats. In the 3rd, 4th and 5th day after ligation the rats received a local injection of different concentrations of opioid antagonists Cyprodime, Naltrindole, or Nor-binaltorphimine, which specifically block mü, delta and kappa opioid receptors, respectively. In the 7th experimental day, rats were euthanized and their maxillae collected for evaluation of alveolar bone and fiber attachment loss, morphometric counting of osteoclasts and osteoblasts, as well as the levels of cytokines IL-1β, IFN-γ, and IL-6 by ELISA.. Selective antagonism of kappa opioid receptors, but not mü and delta, exacerbated alveolar bone resorption induced by ligature in rats. The increased bone loss associated with higher number of osteoclasts surrounding alveolar bone, although osteoblasts' counting remained unchanged. The concentrations of IL-1β and IL-6 in periodontal tissues were also significantly higher in the rats treated with the kappa antagonist.. Inhibiting kappa opioid receptors exacerbates alveolar bone resorption.

Topics: Alveolar Bone Loss; Animals; Bone Resorption; Cytokines; Disease Models, Animal; Male; Morphinans; Naltrexone; Narcotic Antagonists; Osteoblasts; Osteoclasts; Periodontitis; Rats; Rats, Wistar; Receptors, Opioid

Topics: Analgesics, Opioid; Animals; Bone Neoplasms; Cancer Pain; Cell Line, Tumor; Fentanyl; Hydrogen-Ion Concentration; Hyperalgesia; Ligands; Male; Melanoma, Experimental; Mice; Mice, Inbred C3H; Mice, Inbred C57BL; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Piperidines; Receptors, Opioid, mu

Novelty- and sensation-seeking behaviors induce activity of the brain reward system and are associated with increased susceptibility to drug abuse. Endogenous opioids have been implicated in reward-related behavior; however, the involvement of specific opioid receptors in the mechanism of sensation seeking is unknown. Here, we show that selective inhibition of opioid receptors reduce operant sensation seeking in mice. Administration of naltrexone (a nonselective opioid antagonist) reduced instrumental responding for sensory stimuli at one of the tested doses (2 mg/kg). More robust effects were observed in the case of cyprodime, a selective μ opioid receptor antagonist, which reduced instrumental responses by ∼50% at doses of 0.5 mg/kg and larger. Conversely, selective δ and κ receptor antagonists (naltrindole and nor-binaltorphimine, respectively) had no effect on sensation-seeking behavior. Importantly, while naltrexone produces aversion in the conditioned place preference test, cyprodime had no such effect. Therefore, reduced instrumental responding was not correlated with aversive effects of the opioid antagonists. In conclusion, our results revealed a novel mechanism of action of selective opioid receptors antagonists, which may have relevance for their efficacy in the treatment of drug abuse.

Topics: Animals; Appetitive Behavior; Brain; Conditioning, Operant; Dose-Response Relationship, Drug; Exploratory Behavior; Male; Mice, Inbred C57BL; Morphinans; Motivation; Motor Activity; Naltrexone; Narcotic Antagonists; Random Allocation; Receptors, Opioid; Receptors, Opioid, mu; Reward

The use of regional and other opioid-sparing forms of anesthesia has been associated with a decrease in the recurrence of certain malignancies. Direct suppression of human natural killer cells by opioids has been postulated to explain this observation. However, the effect of different classes of opioids on suppression of natural killer cell cytotoxicity has not been systematically characterized.. After confirming that freshly isolated natural killer cells from peripheral human blood express opioid receptors, cells were incubated with increasing concentrations of clinically used or receptor-specific opioid agonists. We also evaluated the effect of pretreatment with receptor-specific antagonists or naloxone. Treated natural killer cells were then coincubated with a carboxyfluorescein succinimidyl ester-labeled target tumor cell line, K562. Annexin V staining was used to compare the percent of tumor cell apoptosis in the presence of opioid-pretreated and untreated natural killer cells. Treated samples were compared to untreated samples using Kruskal-Wallis tests with a post hoc Dunn correction.. Morphine, methadone, buprenorphine, loperamide, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, and U-50488 significantly decreased natural killer cell cytotoxicity. When natural killer cells were pretreated with naloxone, cyprodime, and nor-binaltorphimine before exposure to morphine, there was no difference in natural killer cytotoxicity, compared to the amount observed by untreated natural killer cells. Fentanyl, O-desmethyltramadol, and [D-Pen2,D-Pen5] enkephalin did not change natural killer cell cytotoxicity compare to untreated natural killer cells.. Incubation of isolated natural killer cells with certain opioids causes a decrease in activity that is not observed after naloxone pretreatment. Suppression of natural killer cell cytotoxicity was observed with μ- and κ-receptor agonists but not δ-receptor agonists. These data suggest that the effect is mediated by μ- and κ-receptor agonism and that suppression is similar with many clinically used opioids.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Anesthesia; Buprenorphine; Enkephalin, D-Penicillamine (2,5)-; Fentanyl; Fluoresceins; Humans; Immunosuppression Therapy; K562 Cells; Killer Cells, Natural; Loperamide; Methadone; Morphinans; Morphine; Naloxone; Naltrexone; Succinimides; Toll-Like Receptor 4; Tramadol

We examined the efficacy of tramadol on the urethral reflex during sneezing, as well as the role of µ-opioid receptors in the spinal cord, in rats.. Forty-one female Sprague-Dawley rats were used. The rats were divided into normal female rats and rats with vaginal distension (VD), which mimics stress urinary incontinence (SUI) in humans. Under urethane anesthesia, the sneeze-induced amplitude of urethral responses (AUR) and baseline pressure (BP) were examined after intravenous injection of tramadol using a microtransducer-tipped catheter in both rat groups. The effect of intrathecal cyprodime, a selective µ-opioid receptor antagonist, following intravenous tramadol injection was examined in normal rats. The tilt leak point pressure (tilt LPP) after intravenous tramadol injection was also evaluated in both groups.. In normal rats, tramadol enhanced the AUR and BP by 33.2% and 19.5%, respectively. Tramadol also increased BP by 13.9% in rats with VD, but it did not change AUR. Intrathecal cyprodime alone did not change AUR, but it decreased BP. However, tramadol-provoked increments in AUR were blocked by intrathecal cyprodime, while BP was recovered to the level that it was before administration of cyprodime. Tramadol was associated with a significant elevation in tilt LPP: 24.8% and 19.5% in normal and VD rats, respectively.. These findings suggest that tramadol effectively enhances the AUR at the spinal level and BP peripherally. Therefore, stimulation of the spinal µ-opioid receptors may be useful for the treatment of SUI.

Topics: Anesthetics, Intravenous; Animals; Female; Morphinans; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Reflex; Sneezing; Spinal Cord; Tramadol; Urethane; Urethra; Urinary Incontinence, Stress; Vagina

The opioid system modulates the central reinforcing effects of ethanol and participates in the etiology of addiction. However, the pharmacotherapy of ethanol dependence targeted on the opioid system is little effective and varies due to individual patients' sensitivity. In the present study, we used two mouse lines with high (HA) and low (LA) activity of the endogenous opioid system to analyze the effect of opioid receptor blockade on ethanol drinking behavior. We found that LA and HA lines characterized by divergent magnitudes of swim stress-induced analgesia also differ in ethanol intake and preference. Downregulation of the opioid system in LA mice was associated with increased ethanol consumption. Treatment with a non-selective opioid receptor antagonist (naloxone) had no effect on ethanol intake in this line. Surprisingly, in HA mice, the blockage of opioid receptors led to excessive ethanol consumption. Moreover, naloxone selectively induced high levels of anxiety- and depressive-like behaviors in HA mice which was attenuated by ethanol. With the use of specific opioid receptor antagonists we showed that the naloxone-induced increase in ethanol drinking in HA mice is mediated mainly by δ and to a lower extent by μ opioid receptors. The effect of δ-opioid receptor antagonism was abolished in HA mice carrying a C320T transition in the δ-opioid receptor gene (EU446125.1), which impairs this receptor's function. Our results indicate that high activity of the opioid system plays a protective role against ethanol dependence. Therefore, its blockage with opioid receptor antagonists may lead to a profound increase in ethanol consumption.

Topics: Alcohol Drinking; Analgesia; Analysis of Variance; Animals; beta-Endorphin; Central Nervous System Depressants; Disease Models, Animal; Ethanol; Genotype; Maze Learning; Mice; Mood Disorders; Morphinans; Naloxone; Narcotic Antagonists; Receptors, Opioid, delta; Stress, Psychological; Swimming

Buprenorphine (BPN), a mixed opioid drug with high affinity for mu (MOR) and kappa (KOR) opioid receptors, has been shown to produce behavioral responses in rodents that are similar to those of antidepressant and anxiolytic drugs. Although recent studies have identified KORs as a primary mediator of BPN's effects in rodent models of depressive-like behavior, the role of MORs in BPN's behavioral effects has not been as well explored. The current studies investigated the role of MORs in mediating conditioned approach behavior in the novelty-induced hypophagia (NIH) test, a behavioral measure previously shown to be sensitive to chronic treatment with antidepressant drugs. The effects of BPN were evaluated in the NIH test 24h post-administration in mice with genetic deletion of the MOR (Oprm1

Topics: Animals; Antidepressive Agents; Behavior, Animal; Buprenorphine; Feeding and Eating Disorders; Feeding Behavior; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Naltrexone; Narcotic Antagonists; Pain Measurement; Reaction Time; Receptors, Opioid, kappa; Receptors, Opioid, mu

Previously, we reported that central administration of bombesin, a stress-related peptide, elevated plasma levels of catecholamines (noradrenaline and adrenaline) in the rat. The sympatho-adrenomedullary system, which is an important component of stress responses, can be regulated by the central opioid system. In the present study, therefore, we examined the roles of brain opioid receptor subtypes (µ, δ, and κ) and nociceptin receptors, originally identified as opioid-like orphan receptors, in the bombesin-induced activation of central sympatho-adrenomedullary outflow using anesthetized male Wistar rats. Intracerebroventricularly (i.c.v.) administered bombesin-(1 nmol/animal) induced elevation of plasma catecholamines was significantly potentiated by pretreatment with naloxone (300 and 1000 µg/animal, i.c.v.), a non-selective antagonist for µ-, δ-, and κ-opioid receptors. Pretreatment with cyprodime (100 µg/animal, i.c.v.), a selective antagonist for µ-opioid receptors, also potentiated the bombesin-induced responses. In contrast, pretreatment with naltrindole (100 µg/animal, i.c.v.) or nor-binaltorphimine (100 µg/animal, i.c.v.), a selective antagonist for δ- or κ-opioid receptors, significantly reduced the elevation of bombesin-induced catecholamines. In addition, pretreatment with JTC-801 (30 and 100 µg/animal, i.c.v.) or J-113397 (100 µg/animal, i.c.v.), which are selective antagonists for nociceptin receptors, also reduced the bombesin-induced responses. These results suggest that brain µ-opioid receptors play a suppressive role and that brain δ-, κ-opioid, and nociceptin receptors play a facilitative role in the bombesin-induced elevation of plasma catecholamines in the rat. Thus, in the brain, these receptors could play differential roles in regulating the activation of central sympatho-adrenomedullary outflow.

Topics: Adrenal Medulla; Animals; Bombesin; Brain; Catecholamines; Morphinans; Naloxone; Naltrexone; Nociceptin Receptor; Rats; Receptors, Opioid; Sympathetic Nervous System

In α-chloralose anesthetized cats, we examined the role of opioid receptor (OR) subtypes (µ, κ, and δ) in tibial nerve stimulation (TNS)-induced inhibition of bladder overactivity elicited by intravesical infusion of 0.25% acetic acid (AA). The sensitivity of TNS inhibition to cumulative i.v. doses of selective OR antagonists (cyprodime for µ, nor-binaltorphimine for κ, or naltrindole for δ ORs) was tested. Naloxone (1 mg/kg, i.v., an antagonist for µ, κ, and δ ORs) was administered at the end of each experiment. AA caused bladder overactivity and significantly (P < 0.01) reduced bladder capacity to 21.1% ± 2.6% of the saline control. TNS at 2 or 4 times threshold (T) intensity for inducing toe movement significantly (P < 0.01) restored bladder capacity to 52.9% ± 3.6% or 57.4% ± 4.6% of control, respectively. Cyprodime (0.3-1.0 mg/kg) completely removed TNS inhibition without changing AA control capacity. Nor-binaltorphimine (3-10 mg/kg) also completely reversed TNS inhibition and significantly (P < 0.05) increased AA control capacity. Naltrindole (1-10 mg/kg) reduced (P < 0.05) TNS inhibition but significantly (P < 0.05) increased AA control capacity. Naloxone (1 mg/kg) had no effect in cyprodime pretreated cats, but it reversed the nor-binaltorphimine-induced increase in bladder capacity and eliminated the TNS inhibition remaining in naltrindole pretreated cats. These results indicate a major role of µ and κ ORs in TNS inhibition, whereas δ ORs play a minor role. Meanwhile, κ and δ ORs also have an excitatory role in irritation-induced bladder overactivity.

Topics: Acetic Acid; Animals; Cats; Female; Male; Morphinans; Naloxone; Naltrexone; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Tibial Nerve; Transcutaneous Electric Nerve Stimulation; Urinary Bladder, Overactive

The objective of this study was to evaluate the antinociceptive effects of a lectin from Canavalia brasiliensis (ConBr) when administered orally to murine models of chemical and thermal nociception. ConBr up to 100 mg/kg produced significant and dose-dependent antinociceptive effects: 81% reduction in abdominal writhing induced by 0.6% acetic acid; 26 and 52% reduction in early- and late-stage paw licking, respectively, induced by 2.5% formalin; and 155% increase in reaction latency (heightened thermal pain threshold). In all models, the antinociceptive effect was reversed by the lectin-binding carbohydrate α-d-methyl-mannoside and by the nonselective opioid antagonist naloxone. The antinociceptive effect observed in the formalin test was inhibited by the δ-selective antagonist naltrindole and the κ-selective antagonist nor-binaltorphimine but not by the μ-selective antagonist cyprodime. In conclusion, when administered orally to Swiss mice, the ConBr lectin displayed antinociceptive activity, both peripheral and central, mediated by the opioid system and involving δ-and κ-receptors and the lectin domain.

Topics: Administration, Oral; Analgesics; Analgesics, Opioid; Animals; Canavalia; Mice; Morphinans; Naloxone; Naltrexone; Nociception; Pain Measurement; Plant Lectins; Receptors, Opioid, delta; Receptors, Opioid, kappa; Seeds

MCRT (YPFPFRTic-NH(2)) is a chimeric opioid peptide based on morphiceptin and PFRTic-NH(2). In order to assess the cardiovascular effect of MCRT, it was administered by intravenous (i.v.) injection targeting at the peripheral nervous system and by intracerebroventricular (i.c.v.) injection targeting at the central nervous system. Naloxone and L-NAME were injected before MCRT to investigate possible interactions with MCRT. Results show that administration of MCRT by i.v. or i.c.v. injection could induce bradycardia and decrease in mean arterial pressure (MAP) at a greater degree than that with morphiceptin and PFRTic-NH(2). When MCRT and NPFF were coinjected, we observed a dose-dependent weakening of these cardiovascular effects by MCRT. Because naloxone completely abolished the cardiovascular effects of MCRT, we conclude that opioid receptors are involved in regulating the MAP of MCRT regardless of modes of injection. The effect of MCRT on heart rate is completely dependent on opioid receptors when MCRT was administered by i.c.v. instead of i.v. The central nitric oxide (NO) pathway is involved in regulating blood pressure by MCRT under both modes of injection, but the peripheral NO pathway had no effect on lowering blood pressure mediated by MCRT when it was administered by i.c.v. Based on the results from different modes of injection, the regulation of heart rate by MCRT mainly involves in the central NO pathway. Lastly, we observed that the cardiovascular effects of MCRT such as bradycardia and decrease of blood pressure, were stronger than that of its parent peptides. Opioid receptors and the NO pathway are involved in the cardiovascular regulation by MCRT, and their degree of involvement differs between intravenous and intracerebroventricular injection.

Topics: Analgesics, Opioid; Animals; Blood Pressure; Bradycardia; Endorphins; Heart Rate; Hypotension; Injections, Intravenous; Injections, Intraventricular; Male; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Rats; Rats, Wistar

Rhodiola rosea (Rhodiola) is grown at high altitudes and northern latitudes. It is mainly used clinically as an adaptogen, but antihypertensive effects have been reported for the extract. These have not been well investigated, so in the present study, we evaluated the effect of Rhodiola-water extract on blood pressure in spontaneously hypertensive rats (SHRs) and investigated the potential mechanism(s) for this action. In conscious male SHRs, systolic blood pressure (SBP) and heart rate were recorded using the tail-cuff method. Plasma β-endorphin was measured by enzyme-linked immunosorbent assay. Rhodiola-water extract decreased SBP in SHRs in a dose-dependent manner, and this action was more significant than that in normal group named Wistar-Kyoto (WKY) rats. This reduction of SBP in SHRs was inhibited by pretreatment with the selective opioid μ-receptor antagonist, cyprodime, but not by naloxonazine, an antagonist specific to opioid μ1-receptor. Also, the SBP-lowering action of Rhodiola-water extract was attenuated in adrenalectomized SHRs. Moreover, Rhodiola-water extract dose-dependently increased β-endorphin release in SHRs, and the elevation of β-endorphin in SHRs was higher than that in WKY. Thus, we suggest that Rhodiola-water extract can induce release of β-endorphin to lower SBP in SHRs.

Topics: Animals; Antihypertensive Agents; beta-Endorphin; Blood Pressure; Heart Rate; Male; Morphinans; Plant Extracts; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rhodiola

To investigate the role of opioid μ-receptor subtype in opiate-induced constipation (OIC).. The effect of loperamide on intestinal transit was investigated in mice. Ileum strips were isolated from 12-wk-old male BALB/c mice for identification of isometric tension. The ileum strips were precontracted with 1 μmol/L acetylcholine (ACh). Then, decrease in muscle tone (relaxation) was characterized after cumulative administration of 0.1-10 μmol/L loperamide into the organ bath, for a concentration-dependent study. Specific blockers or antagonists were used for pretreatment to compare the changes in loperamide-induced relaxation.. In addition to the delay in intestinal transit, loperamide produced a marked relaxation in isolated ileum precontracted with ACh, in a dose-dependent manner. This relaxation was abolished by cyprodime, a selective opioid μ-receptor antagonist, but not modified by naloxonazine at a dose sufficient to block opioid μ-1 receptors. Also, treatment with opioid μ-1 receptor agonist failed to modify the muscle tone. Moreover, the relaxation by loperamide was attenuated by glibenclamide at a dose sufficient to block ATP-sensitive K+ (K(ATP)) channels, and by protein kinase A (PKA) inhibitor, but was enhanced by an inhibitor of phosphodiesterase for cyclic adenosine monophosphate (cAMP).. Loperamide induces intestinal relaxation by activation of opioid μ-2 receptors via the cAMP-PKA pathway to open K(ATP) channels, relates to OIC.

Topics: Acetylcholine; Analgesics, Opioid; Animals; Antidiarrheals; Constipation; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Gastrointestinal Transit; Glyburide; Humans; Intestine, Small; Loperamide; Male; Mice; Mice, Inbred BALB C; Morphinans; Muscle Relaxation; Naloxone; Receptors, Opioid, mu

A chimeric opioid peptide (MCRT, YPFPFRTic-NH(2)) was here designed and synthesized. This peptide was based on morphiceptin (YPFP-NH(2)) and a neuropeptide FF (NPFF) derivative (PFRTic-NH(2)) sharing one proline. This peptide is intended to produce potent analgesia. MCRT was found to induce analgesic activity in a dose- and time-dependent manner, as indicated by a tail flick latency test in mice to which it had been intracerebroventricularly administered (5-60 min, 0.025-2.5 nmol/kg (0.5-50 pmol per mouse), ED(50)=1.49 nmol/kg). At 2.5nmol/kg, MCRT showed significantly higher levels of analgesic activity than morphiceptin or PFR(Tic)amide at 2500 nmol/kg. Naltrindole and cyprodime were found to partially but significantly inhibit this analgesic activity, but naloxone blocked it completely. The kappa opioid receptor antagonist nor-BNI was found to slightly inhibit MCRT and morphiceptin. Pre-injection of BIBP3226 and co-administration of NPFF and MCRT showed that NPFF receptors were involved in the analgesia of MCRT. BIBP3226 was found to weaken the analgesic effects of MCRT, but BIBP3226 could not block the analgesic effects of PFR(Tic)amide. Overall, MCRT was found to have stronger analgesic activity than morphiceptin or PFR(Tic)amide when interacting with mixed μ/δ opioid receptor interactions. MCRT also showed partial interaction with NPFF receptors.

Topics: Analgesia; Analgesics, Opioid; Animals; Arginine; Dose-Response Relationship, Drug; Endorphins; Guinea Pigs; Male; Mice; Morphinans; Naloxone; Naltrexone; Neuropeptides; Opioid Peptides; Proline; Receptors, Neuropeptide; Tetrahydroisoquinolines; Time Factors

The role of opioid receptors in the regulation of vascular function remains unclear. In the current study, we evaluated the ability of loperamide, a peripheral opioid receptor agonist, to regulate blood pressure in spontaneously hypertensive rats (SHRs) and examined the mechanism(s) by which loperamide exerts its effects.. In male SHRs, mean arterial pressure (MAP) was measured and hemodynamic analysis was recorded. Additionally, the isometric tension of aortic rings isolated from SHRs was determined.. Loperamide dose-dependently decreased MAP in SHRs but not in the normal group of Wistar-Kyoto rats. This reduction of MAP in conscious SHRs was abolished by the selective opioid μ-receptor antagonist cyprodime, but not by naloxonazine, the μ(1)-opioid receptor antagonist. However, cardiac output was not altered by loperamide in anesthetized SHRs. Moreover, loperamide-induced relaxation in isolated aortic rings precontracted with phenylephrine or vasopressin. This relaxation was abolished by cyprodime, but not by naloxonazine. Loperamide-induced relaxation was also attenuated by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. Additionally, vasodilatation by loperamide was reduced by an inhibitor of protein kinase A (PKA) and enhanced by an inhibitor of phosphodiesterases.. We suggest that loperamide can lower MAP in SHRs via μ(2)-opioid receptor-dependent cAMP-PKA pathway that induces vascular relaxation by opening K(ATP) channels.

Topics: Animals; Arteries; Blood Pressure; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Endothelium; Glyburide; Hemodynamics; Intracellular Signaling Peptides and Proteins; KATP Channels; Loperamide; Male; Morphinans; Naloxone; Phenylephrine; Phosphodiesterase Inhibitors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Opioid, mu; Vasodilation

7-Hydroxymitragynine is a potent opioid analgesic alkaloid isolated from the Thai medicinal herb Mitragyna speciosa. In the present study, we investigated the opioid receptor subtype responsible for the analgesic effect of this compound. In addition, we tested whether development of tolerance, cross-tolerance to morphine and naloxone-induced withdrawal signs were observed in chronically 7-hydroxymitragynine-treated mice. Subcutaneous (s.c.) administration of 7-hydroxymitragynine produced a potent antinociceptive effect mainly through activation of mu-opioid receptors. Tolerance to the antinociceptive effect of 7-hydroxymitragynine developed as occurs to morphine. Cross-tolerance to morphine was evident in mice rendered tolerant to 7-hydroxymitragynine and vice versa. Naloxone-induced withdrawal signs were elicited equally in mice chronically treated with 7-hydroxymitragynine or morphine. 7-Hydroxymitragynine exhibited a potent antinociceptive effect based on activation of mu-opioid receptors and its morphine-like pharmacological character, but 7-hydroxymitragynine is structurally different from morphine. These interesting characters of 7-hydroxymitragynine promote further investigation of it as a novel lead compound for opioid studies.

Topics: Analgesics; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Drug Tolerance; Injections, Subcutaneous; Male; Mice; Mitragyna; Models, Molecular; Morphinans; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Pain Measurement; Reaction Time; Secologanin Tryptamine Alkaloids; Substance Withdrawal Syndrome; Thailand

The stimulation of peripheral opioid receptors yields analgesic responses in a model of bone cancer-induced pain in mice. In order to know the type(s) of peripheral opiate receptors involved, the paw thermal withdrawal latencies were measured in C3H/HeJ mice bearing a tibial osteosarcoma, after administering selective agonists of mu-,delta-and kappa-opiate receptors. The peritumoral administration of DAGO (0.6-6 microg) inhibited the osteosarcoma-induced hyperalgesia at doses ineffective in healthy animals, the highest one even increasing the withdrawal latencies over the control values. Naloxone-methiodide (2 mg/kg) and cyprodime (1 mg/kg), but not naltrindole (0.1 mg/kg) nor nor-binaltorphimine (10 mg/kg), antagonized DAGO-induced analgesic effects, these therefore probably being mediated through peripheral mu-opioid receptors. The peritumoral injection of DPDPE (100 microg) induced analgesia which was inhibited by naloxone-methiodide and naltrindole but not by nor-binaltorphimine. Cyprodime partially antagonized the analgesia induced by 100 microg of DPDPE, but did not modify the effect induced by 30 microg of this agonist-a dose that restores the hyperalgesic latencies up to the control values. The antihyperalgesic effect induced by the peritumoral administration of U-50,488H (1 microg) was antagonized by naloxone-methiodide and nor-binaltorphimine, but not by cyprodime nor naltrindole, thus suggesting the involvement of peripheral kappa-opioid receptors. In conclusion, the stimulation of peripheral mu-, delta- and kappa-opioid receptors is a pharmacological strategy useful for relieving this experimental type of bone cancer-induced pain, the greatest analgesic effect being achieved by stimulating peripheral mu-opioid receptors.

Topics: Analgesics, Opioid; Animals; Bone Neoplasms; Drug Interactions; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Hyperalgesia; Mice; Morphinans; Naltrexone; Narcotic Antagonists; Osteosarcoma; Receptors, Opioid

The synthesis, biological, and pharmacological evaluation of novel derivatives of cyprodime are described. Their binding affinities at mu, delta, and kappa opioid receptors were evaluated using receptor binding assay. It was observed that the affinity of these compounds was sensitive to the character and length of the substituent in position 4. Further prolongation of the 4-alkoxy group of cyprodime (1) and its 4-butoxy analogue 2 is detrimental for the mu opioid receptor affinity. Introduction of an arylalkoxy group at C-4 does not increase mu affinity in the case of benzyloxy, while a phenylpropoxy group reduces mu affinity. The delta and kappa affinities were also reduced compared to the reference compounds. A significant increase in the affinity at the mu opioid receptors was achieved by introducing a 14-phenylpropoxy group. Increases in the affinity at delta and kappa receptors were also observed. These findings provide further evidence that the nature of the substituent at position 14 has a major impact on the abilities of morphinans to interact with opioid receptors. In the [(35)S]GTPgammaS binding assay, all tested compounds were partial agonists at mu and delta receptors. Compounds 8 and 17 showed antagonism at kappa receptors, while compound 7 exhibited some partial agonist activity at this receptor. The novel derivatives of cyprodime containing a 14-phenylpropoxy group acted as potent antinociceptives. When tested in vivo, compounds 7, 8, and 17 were considerably more potent than morphine, with phenol 7 showing the highest antinociceptive potency (21-fold in the hot plate test, 38-fold in the tail flick test, and 300-fold in the paraphenylquinone writhing test) in mice. Introduction of a 14-phenylpropoxy substituent leads to a profound alteration in the pharmacological profile of this class of compounds.

Topics: Analgesics, Opioid; Animals; Binding, Competitive; CHO Cells; Cricetinae; In Vitro Techniques; Mice; Morphinans; Radioligand Assay; Rats; Receptors, Opioid, mu; Structure-Activity Relationship

Co-localization of opioid and melanocortin receptor expression, especially at the spinal cord level in the dorsal horn and in the gray matter surrounding the central canal led to the suggestion that melanocortins might play a role in nociceptive processes. In the present studies, we aimed to determine the effects of melanocortins, administered intrathecally, on allodynia, and to ascertain whether there is an interaction between opioid and melanocortin systems at the spinal cord level. Neuropathic pain was induced by chronic constriction injury (CCI) of the right sciatic nerve in rats. Tactile allodynia was assessed using von Frey filaments, while thermal hyperlagesia was evaluated in cold water allodynia test. In the present experiments, melanocortin receptor antagonist, SHU9119 was much more potent than mu-opioid receptor agonist, morphine after their intrathecal (i.th.) administration in neuropathic rats. SHU9119 alleviated allodynia in a comparable manner to DAMGO, a selective and potent mu-opioid receptor agonist. Administration of melanocortin receptor agonist, melanotan-II (MTII) increased the sensitivity to tactile and cold stimulation. Moreover, we demonstrated that the selective blockade of mu-opioid receptor by cyprodime (CP) enhanced antiallodynic effect of SHU9119 as well as pronociceptive action of MTII, whereas the combined administration of mu receptor agonist (DAMGO) and SHU9119 significantly reduced the analgesic effect of those ligands. DAMGO also reversed the proallodynic effect of melanocortin receptor agonist, MTII. In conclusion, it seems that the endogenous opioidergic system acts as a functional antagonist of melanocortinergic system, and mu-opioid receptor activity appears to be involved in the modulation of melanocortin system function.

Topics: alpha-MSH; Analgesics, Opioid; Animals; Chronic Disease; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Injections, Spinal; Male; Melanocyte-Stimulating Hormones; Morphinans; Morphine; Nociceptors; Oligopeptides; Rats; Rats, Wistar; Receptor, Melanocortin, Type 4; Receptors, Corticotropin; Receptors, Opioid, mu; Sciatica; Spinal Cord

The R and S enantiomers of [(11)C]GR89696, [(11)C]-methyl 4-[(3,4-dichlorophenyl)acetyl]-3-[(1-pyrrolidinyl)methyl]-1-piperazinecarboxylate, were synthesized from their appropriate chiral precursors and [(11)C]methyl chloroformate. The [(11)C]-labeled R enantiomer of GR89696, also known as GR103545, demonstrated high affinity in mouse brain with region to cerebellar ratios at 90 minutes of 11.4 and 8.7 for the hypothalamus and olfactory tubercle, respectively. The [(11)C]-labeled S enantiomer showed low affinity and region to cerebellar ratios of 1 for all brain regions. The [(11)C]-labeled GR103545 exhibited a selective and saturable binding for the kappa opioid receptor.

Topics: Adrenergic alpha-Agonists; Animals; Brain; Mice; Morphinans; Naltrexone; Narcotic Antagonists; Piperazines; Pyrrolidines; Receptors, Opioid, kappa; Stereoisomerism; Tissue Distribution

Long-term treatment of Parkinson's disease with levodopa is complicated by the emergence of involuntary movements, known as levodopa-induced dyskinesia. It has been hypothesized that increased opioid transmission in striatal output pathways may be responsible for the generation of dyskinesia. In this study, we have investigated the effect of blockade of opioid peptide transmission on levodopa-induced dyskinesia in a primate model of Parkinson's disease-the MPTP-lesioned marmoset. Coadministration of nonselective and mu- or delta-subtype-selective opioid receptor antagonists with levodopa resulted in a significant decrease in dyskinesia. There was no attenuation of the anti-parkinsonian actions of levodopa. These data suggest that specific mu- or delta-opioid receptor antagonists might be applicable clinically in the treatment of levodopa-induced dyskinesia in Parkinson's disease.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Callithrix; Disease Models, Animal; Drug Therapy, Combination; Dyskinesias; Female; Hypokinesia; Levodopa; Male; Morphinans; Motor Activity; Naltrexone; Narcotic Antagonists; Parkinsonian Disorders; Posture; Receptors, Opioid, delta; Receptors, Opioid, mu

1. Although cholecystokinin octapeptide sulphate (CCK-8) activates the opioid system of isolated guinea-pig ileum (GPI) whether it activates the mu- or kappa-system, or both, remains unclear. Neither is it known whether CCK-8 influences the withdrawal responses in GPI preparations briefly exposed to opioid agonists. This study was designed to clarify whether CCK-8 activates mu- or kappa-opioid systems or both; and to investigate its effect on the withdrawal contractures in GPI exposed to mu- or kappa-agonists and on the development of tolerance to the withdrawal response. 2. In GPI exposed to CCK-8, the selective kappa-antagonist nor-binaltorphimine elicited contractile responses that were concentration-related to CCK-8 whereas the selective mu-antagonist cyprodime did not. 3. In GPI preparations briefly exposed to the selective mu-agonist, dermorphin, or the selective kappa-agonist, U-50, 488H, and then challenged with naloxone, CCK-8 strongly enhanced the withdrawal contractures. 4. During repeated opioid agonist/CCK-8/opioid antagonist tests tolerance to opioid-induced withdrawal responses did not develop. 5. These results show that CCK-8 preferentially activates the GPI kappa-opioid system and antagonizes the mechanism(s) that control the expression of acute dependence in the GPI.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphinans; Muscle Contraction; Naloxone; Naltrexone; Oligopeptides; Opioid Peptides; Receptor, Cholecystokinin A; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Receptors, Opioid; Sincalide; Substance Withdrawal Syndrome

Evidence suggests that the antinociceptive effects of selective delta-opioid receptor agonists may involve an activation of the mu-receptor in some experimental conditions. The aim of this study was to clarify the receptors involved in the antinociceptive responses of the selective and systemically active delta-opioid receptor agonist Tyr-D-Ser-(O-tert-butyl)-Gly-Phe-Leu-Thr-(O-tert-butyl) (BUBU). The antinociception induced by systemic (i.v.) or central (i.c.v.) administration of BUBU was measured in the hot plate (jumping and paw lick latencies) and tail immersion tests in mice. In both tests, the responses were more intense when BUBU was administered by central route. The pre-treatment with the mu-opioid receptor antagonist cyprodime blocked the effects induced by central BUBU in the hot plate and tail immersion tests. The delta-opioid receptor antagonist naltrindole had no effect on BUBU-induced antinociception in the hot plate but decreased BUBU responses in the tail immersion test. Further evidence for this dual receptor action of BUBU was demonstrated by using antisense oligodeoxynucleotides. Thus, a reduction in central BUBU-induced antinociception was observed in the tail immersion test after the administration of antisense probes that selectively blocked the expression of mu- or delta-opioid receptors. These findings clearly indicate using a dual pharmacological and molecular approach that BUBU mediates its antinociceptive effects via activation of both mu- and delta-opioid receptors.

Topics: Analgesics; Animals; Male; Mice; Morphinans; Naltrexone; Narcotic Antagonists; Oligonucleotides, Antisense; Oligopeptides; Pain Measurement; Receptors, Opioid, delta; Receptors, Opioid, mu

The use of compounds with high selectivity for each opioid receptor (mu, delta and kappa) is crucial for understanding the mechanisms of opioid actions. Until recently non-peptide mu-opioid receptor selective antagonists were not available. However, N-cyclopropylmethyl-4,14-dimethoxy-morphinan-6-one (cyprodime) has shown a very high selectivity for mu-opioid receptor in in vivo bioassays. This compound also exhibited a higher affinity for mu-opioid receptor than for delta- and kappa-opioid receptors in binding assays in brain membranes, although the degree of selectivity was lower than in in vitro bioassays. Cyprodime has recently been radiolabelled with tritium resulting in high specific radioactivity (36.1 Ci/mmol). We found in in vitro binding experiments that this radioligand bound with high affinity (K(d) 3. 8+/-0.18 nM) to membranes of rat brain affording a B(max) of 87. 1+/-4.83 fmol/mg. Competition studies using mu, delta and kappa tritiated specific ligands confirmed the selective labelling of cyprodime to a mu-opioid receptor population. The mu-opioid receptor selective agonist [D-Ala(2),N-MePhe(4),Gly(5)-ol]enkephalin (DAMGO) was readily displaced by cyprodime (K(i) values in the low nanomolar range) while the competition for delta- ([D-Pen(2), D-Pen(5)]enkephalin (DPDPE)) and kappa- (5alpha,7alpha, 8beta-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4, 5)dec-8-yl]-benzene-acetamide (U69,593)) opioid receptor selective compounds was several orders of magnitude less. We also found that cyprodime inhibits morphine-stimulated [35S]GTPgammaS binding. The EC(50) value of morphine increased about 500-fold in the presence of 10 microM cyprodime. These findings clearly indicate that cyprodime is a useful selective antagonist for mu-opioid receptor characterization.

Topics: Animals; Binding, Competitive; Brain Chemistry; Guanosine 5'-O-(3-Thiotriphosphate); Guinea Pigs; In Vitro Techniques; Ligands; Membranes; Morphinans; Morphine; Narcotic Antagonists; Narcotics; Radioligand Assay; Radiopharmaceuticals; Rats; Rats, Wistar; Receptors, Opioid, mu; Sulfur Radioisotopes

Relationship between activation of opioid receptors and muscarinic autoinhibition in acetylcholine (ACh) release from the myenteric plexus was studied in longitudinal muscle myenteric plexus (LMMP) preparations of guinea pig ileum. A mu-receptor agonist, [D-Ala2, N-Me-Phe4, Gly5-ol] enkephalin (DAMGO), at a concentration of 1 microM inhibited the ACh release evoked by electrical field stimulation (EFS) at 1 Hz but not at 10 Hz. After the muscarinic autoreceptors were blocked with atropine (1 microM), DAMGO inhibited EFS-evoked ACh release also at 10 Hz. After the autoreceptors were potently activated with muscarine (200 microM), the inhibitory effect of DAMGO at 1 Hz was abolished. A kappa-receptor agonist, U-50,488, at 1 microM inhibited the EFS-evoked ACh release both at 1 and 10 Hz. U-50,488 inhibited ACh release regardless of the presence of atropine or muscarine. A delta-agonist, enkephalin [D-PEN2.5] (PDPDE), did not show any significant effect. On the other hand, a selective mu-receptor antagonist, cyprodime, increased ACh release evoked by EFS at 1 Hz, but not at 10 Hz. After the autoreceptors were blocked, cyprodime increased EFS-evoked ACh release also at 10 Hz. The selective kappa-receptor antagonist, nor-binaltorphimine, did not affect ACh release in the absence or presence of atropine. The results suggest that endogenous opioid(s) inhibits ACh release by activating mu-, but not kappa- and delta-receptors in the LMMP of guinea pig ileum and that the inhibitory effect of endogenous opioid(s) in the ACh release is important when muscarinic autoinhibition mechanism does not fully work.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Acetylcholine; Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Atropine; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphinans; Muscarine; Muscarinic Agonists; Muscarinic Antagonists; Muscle, Smooth; Myenteric Plexus; Naltrexone; Narcotic Antagonists; Opioid Peptides; Receptors, Muscarinic; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

Endomorphin-1 and -2, putative endogenous ligands for the mu-opioid receptor, inhibited acetylcholine (ACh) release evoked by electrical field stimulation (EFS) at 1 Hz, which partially activates muscarinic autoreceptors, but not at 10 Hz, which fully activates muscarinic autoreceptors, in longitudinal muscle with the myenteric plexus (LMMP) preparations of guinea pig ileum. After blockade of autoinhibition by atropine, the peptides also inhibited EFS-evoked ACh release at 10 Hz. The inhibitory effects on ACh release were abolished by the mu-opioid antagonist cyprodime. These results suggest that endomorphin-1 and -2 inhibit ACh release from LMMP preparations of guinea pig ileum and that the mechanism of the inhibition must have a component in common with muscarinic autoinhibition.

Topics: Acetylcholine; Amino Acid Sequence; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Electric Stimulation; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphinans; Myenteric Plexus; Narcotic Antagonists; Oligopeptides; Receptors, Opioid, mu

The PNS was anticipated to be involved in the modulation of immune responses. To study aspects of this neuronal-immune communication, a recently developed tissue slice method was used to study the effects of adrenergic and opioidergic transmitters on interleukin 6 (IL-6) secretion in the spleen. The alpha 2-adrenergic agonist p-aminoclonidine (10(-7) M) inhibited IL-6 secretion (control vs. p-aminoclonidine, 100.0 +/- 4.76 vs. 59.3 +/- 6.6% of control values; p < 0.001). The alpha 1-adrenergic agonist methoxamine (10(-8) M) also inhibited IL-6 secretion (100.0 +/- 4.8 vs. 71.5 +/- 3.8%; p < 0.001). The endogenous opioids beta-endorphin (10(-10) M), methionine-enkephalin (10(-9) M), and leucine-enkephalin (10(-9) M) inhibited IL-6 secretion as well (p = 0.0051, p = 0.0337, and p = 0.0226, respectively). Electrical stimulation of spleen slices inhibited IL-6 secretion (100.0 +/- 4.3 vs. 56.7 +/- 4.6% of control values; p < 0.001). The involvement of alpha-adrenergic and opioidergic molecules in this electrically induced inhibition was shown by the use of antagonists. Electrical inhibition of IL-6 secretion was attenuated by phentolamine (10(-7) M; p = 0.0345), by naloxone (10(-6) M; p = 0.0046), by cyprodime (10(-8) M; p = 0.0014), and by the combination of cyprodime (10(-7) M) plus phentolamine (10(-8) M; p < 0.0001). We conclude from the complementary studies that the inhibition of IL-6 secretion induced by electrical pulses was mostly mediated by alpha-adrenergic and mu-opioidergic endogenous transmitters.

Topics: Adrenergic alpha-Agonists; Adrenergic beta-Agonists; Analgesics; Animals; beta-Endorphin; Clonidine; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Methionine; Enkephalins; Female; Interleukin-6; Isoproterenol; Mice; Mice, Inbred Strains; Morphinans; Naloxone; Narcotic Antagonists; Neurons; Phentolamine; Propranolol; Receptors, Adrenergic, alpha; Receptors, Adrenergic, beta; Receptors, Opioid; Spleen

The head kidney is the main lymphopoietic organ of teleost fish. It is the source of leukocytes inhabiting the peritoneal cavity during an experimental peritoneal inflammation (Gruca et al., Folia Biol.-Kraków, 1997, 44, 137-142). The number of elicited peritoneal leukocytes is significantly lower in the goldfish with concomitant morphine injection than in their counterparts injected with the irritant only. Morphine may act directly on the head kidney leukocytes, as they are equipped with the selective naloxone-binding sites (Chadzińska et al., Arch. Immunol. Ther. Exp., 1997, in press). Further characterization of these opioid receptors (by radioligand binding techniques) indicates that the goldfish head kidney leukocytes possess at least two different opiate-binding sites: the [3H]naloxone binding site with a KD = 87 +/- 2.1 nM and Bmax = 298 +/- 15 fmol/mg protein; and the second, the [3H]naltrindole binding site with a KD = 37 +/- 5.5 nM and Bmax = 1,172 +/- 220 fmol/mg protein. The competition experiments with delta- (naltrindole), kappa- (nor-binaltorphimine) and mu- (cyprodime, naltrexone) selective ligands suggest that the naloxone-binding site is similar to mu 3 receptors described by Stefano et al. (Proc. Nat. Acad. Sci. USA, 1993, 90 11099-11103). Low affinity binding of selective ligands excludes the presence of neuronal-type mu- and delta-opioid receptors on goldfish leukocytes.

Topics: Animals; Binding Sites; Goldfish; Leukocytes; Morphinans; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Receptors, Opioid, delta; Receptors, Opioid, mu

The aim of the present study was to investigate the role of different endogenous opioid systems in the expression of ethanol's discriminative stimulus effects in a two-lever operant drug discrimination paradigm. Wistar rats trained to make differential responses following the administration of ethanol (1 g/kg, i.p.) or saline. The correct response (fixed-ratio schedule; FR10) resulted in the presentation of food. Once rats had acquired the discrimination an ethanol dose-response test was conducted. The effects of opioid antagonists on the discrimination were assessed by administering the mu-opioid receptor antagonists naloxone (0.5-20 mg/kg s.c.) and cyprodime (5-100 mg/kg s.c.) and the delta-opioid receptor antagonist naltrindole (0.1-25 mg/kg s.c.) 15-30 min before the discrimination test. Furthermore, the selective kappa-opioid antagonist nor-binaltorphimine (5 mg/kg s.c.) given 24 h before the test session was examined. Results of generalization testing demonstrate that ethanol discrimination was dose dependent. Pretreatment with naloxone produced only at the highest dose a partial, but significant, antagonism, whereas cyprodime failed to alter the ethanol cue. This suggested the involvement of other opioid receptor subtypes. However, neither naltrindole nor nor-binaltorphimine had any effect on the ethanol-saline discrimination. These results demonstrate that the expression of the ethanol cue is only partly dependent on the function of endogenous opioid systems.

Topics: Animals; Discrimination, Psychological; Dose-Response Relationship, Drug; Ethanol; Male; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Wistar

The type of opioid receptors involved in the conditioned enhancement of natural killer (NK) cell activity is identified in the present study. In our previous observations, we have demonstrated that the conditioned enhancement of NK cell activity was dependent on beta-endorphin and methionine-enkephalin, but not dynorphin. Based on the interaction of opioids with their homologous receptors, we concluded that mu- and delta-opioid receptors might be involved. To further classify the type(s) of opioid receptors involved in eliciting the conditioned NK cell activity, three opioid receptor antagonists, cyprodime hydrobromide, ICI-174864, and nor-binaltorphimine dihydrochloride, were used to block the conditioned NK cell activity in BALB/c mice. Blocking was conducted by intracisternal injection of the drugs. The results showed that the activation of mu-opioid receptors was required in the conditioned enhancement of NK cell activity, but not the delta- or kappa-type of receptors.

Topics: Animals; beta-Endorphin; Enkephalin, Leucine; Enkephalin, Methionine; Injections, Spinal; Killer Cells, Natural; Mice; Mice, Inbred BALB C; Morphinans; Naltrexone; Narcotic Antagonists; Receptors, Opioid, mu

We have studied the effects of mu- and kappa-opioid receptor blockade on endogenous acetylcholine and noradrenaline overflow from the myenteric plexus of the guinea-pig isolated colon. Cyprodime (putative mu-selective antagonist) and nor-binaltorphimine (kappa-selective antagonist) had a concentration-dependent facilitatory effect on both acetylcholine and noradrenaline overflow. Moreover, in colonic specimens obtained from sympathetically denervated animals, the effect of opioid antagonists on acetylcholine overflow was significantly higher with respect to normal preparations. Evidence is thus given in favour of an involvement of mu- and kappa-opioid receptor pathways in the tonic modulation of neurotransmitter release at the colonic level. Enhanced sensitivity to the effect of mu and kappa antagonists after chronic sympathetic denervation is strongly suggestive for the existence of a functional link between opioid and adrenergic pathways in this model.

Topics: Acetylcholine; Animals; Colon; Dose-Response Relationship, Drug; Guinea Pigs; Morphinans; Myenteric Plexus; Naltrexone; Narcotic Antagonists; Neurotransmitter Agents; Norepinephrine; Receptors, Opioid, kappa; Receptors, Opioid, mu; Sympathetic Nervous System

A series of 3-hydroxy-substituted analogues (3-7) of the mu selective opioid antagonist cyprodime has been synthesized in order to evaluate the role of a hydroxy group at C-3 concerning mu opioid antagonist selectivity. Compounds 3-7 were tested in bioassays (electrical stimulated mouse vas deferens preparation and myenteric-plexus longitudinal muscle preparation of the guinea pig ileum) and opioid receptor binding assays. Antagonism of mu receptor-mediated responses induced by the mu selective agonist DAMGO afforded equilibrium dissociation constants in the mouse vas deferens preparation (Ke values) for compounds 3-7 which agreed closely with their affinities as determined by opioid receptor binding assays (Ki values). At kappa and delta receptors differences were apparent. Although the compounds had high affinity for both kappa and delta receptors in opioid receptor binding, they were very poor at antagonizing agonist responses mediated by kappa and particularly delta agonists in the mouse vas deferens preparation. None of the compounds tested showed agonist potency in the mouse vas deferens preparation or the myenteric-plexus longitudinal muscle preparation of the guinea pig ileum.

Topics: Animals; Brain; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphinans; Muscles; Myenteric Plexus; Narcotic Antagonists; Structure-Activity Relationship; Vas Deferens

This study investigates the possible involvement of opioid receptors in the action of a variety of anticonvulsant agents. The opioid antagonist naloxone (0.3, 1 mg/kg IP) and the selective mu-opioid antagonist cyprodime (3 mg/kg IP) significantly inhibited the increase in electroshock seizure threshold induced by phenytoin (3 mg/kg IP) in mice. The anticonvulsant effects of ethanol (1 g/kg IP) were also significantly antagonised by naloxone (1 mg/kg IP) but not by a 0.3 mg/kg IP dose or by cyprodime (3 mg/kg IP). The results with naloxone were confirmed using higher doses of phenytoin (10 mg/kg IP) and ethanol (1.5 g/kg IP). In contrast to the above findings, naloxone (0.3, 1 mg/kg IP) had no effect on the increase in seizure threshold induced by sodium valproate (200 mg/kg IP) or dizocilpine (MK801, 0.5 mg/kg IP) and paradoxically potentiated the increase in seizure threshold produced by phenobarbitone (15 mg/kg IP); carbamazepine (10 mg/kg IP) and the benzodiazepine agonist loprazolam (1 mg/kg IP), clearly differentiating these compounds from phenytoin and ethanol. These findings suggest that the anticonvulsant effects of phenytoin and ethanol (as assessed by their ability to prevent tonic hindlimb extension in the mouse electroshock model) may be mediated, at least in part, by the release of endogenous opioids and subsequent activation of opioid receptors (mu, in the case of phenytoin, but non-mu, in the case of ethanol) although direct activity at opioid receptors cannot be precluded.

Topics: Animals; Anticonvulsants; Dose-Response Relationship, Drug; Electroshock; Male; Mice; Mice, Inbred Strains; Morphinans; Naloxone; Narcotic Antagonists; Phenytoin; Receptors, Opioid; Receptors, Opioid, mu; Seizures

The effects of the selective opioid antagonists cyprodime (mu; 1, 3, 10, 30 mg/kg IP), norbinaltorphimine (kappa; 3, 10, 30 mg/kg IP) and naltrindole (delta; 0.3, 1, 3, 10 mg/kg IP) on electroshock seizure threshold in mice were compared with those of the universal opioid antagonist naloxone (0.3, 1, 10 mg/kg IP). Seizure threshold was increased by mu-receptor blocking doses of both cyprodime and naloxone, unaltered by norbinaltorphimine and decreased (in a dose-related manner) by all doses of naltrindole. The effects of naltrindole were similar to those of the established pro-convulsant agent bicuculline (1 mg/kg IP); however, naloxone and cyprodime produced relatively small increases in seizure threshold when compared with phenytoin (doses up to 30 mg/kg IP). The differential effects of mu-, kappa- and delta-receptor antagonists obtained in this study suggest that electroshock seizure threshold in mice may be controlled, at least in part, by a balance between endogenous opioids acting either pro-convulsantly through mu-receptors or anti-convulsantly via delta-receptors.

Topics: Animals; Anticonvulsants; Bicuculline; Dose-Response Relationship, Drug; Electroshock; gamma-Aminobutyric Acid; Indoles; Male; Mice; Mice, Inbred Strains; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Phenytoin; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

N-Cyclopropylmethyl-4,14-dimethoxymorphinan (4) and N-cyclopropylmethyl-4-hydroxy-14-methoxymorphinan (5) have been prepared from cyprodime (1) by Wolff-Kishner reduction. Pharmacological studies (mouse vas deferens and guinea pig ileum preparations) revealed that there was no significant decrease of 4 in antagonist activity but in mu selectivity when compared with 1. The phenol 5 showed partial agonism at mu, kappa and delta receptors.

Topics: Animals; Guinea Pigs; Ileum; In Vitro Techniques; Male; Mice; Morphinans; Narcotic Antagonists; Receptors, Opioid; Receptors, Opioid, mu; Vas Deferens

Topics: Animals; In Vitro Techniques; Male; Mice; Morphinans; Narcotic Antagonists; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Structure-Activity Relationship; Vas Deferens

A series of cyprodime-related compounds (2, 4-12, and 26) has been synthesized and evaluated for opioid agonist and antagonist activity with the mouse vas deferens and guinea pig ileum preparations. None of the changes to cyprodime, including the introduction of a 3-OMe group, increasing and decreasing the size of or completely removing the substituent in position 4, replacing the N-cyclopropylmethyl group with an N-allyl group, or replacing the 14-OMe with an 14-OEt substituent, resulted in an improved mu antagonist profile and most were detrimental either in terms of mu selectivity and potency or increased agonist activity. Increasing the length of the substituent in position 4 resulted in a compound (6a) with a very similar profile to that of cyprodime.

Topics: Animals; Chemical Phenomena; Chemistry; Guinea Pigs; Ileum; Male; Mice; Morphinans; Narcotic Antagonists; Receptors, Opioid; Structure-Activity Relationship; Vas Deferens

(-)-N-(Cyclopropylmethyl)-4,14-dimethoxymorphinan-6-one (2) was synthesized with 4,14-dimethoxy-N-methylmorphinan-6-one (1) as starting material. In vivo and in vitro experiments show 2 (cyprodime) to be a pure opioid receptor antagonist. Some of these tests (opioid receptor binding assays, guinea pig ileal longitudinal muscle preparation, rat and mouse vas deferens preparation, acetic acid writhing antagonism test) indicate that 2 is a selective mu opioid receptor antagonist.

Topics: Animals; Guinea Pigs; In Vitro Techniques; Male; Mice; Morphinans; Narcotic Antagonists; Rats; Receptors, Opioid; Receptors, Opioid, mu