AIMTo compare the antagonistic effects of 6 beta-naltrexol and naltrexone against morphine analgesia.

METHODSThe effects of 6 beta-naltrexol and naltrexone against morphine analgesia were observed in mouse heat radiant tail-flick assay and in mouse (55 +/- 1) degrees C hot plate test. The displacement of 6 beta-naltrexol and naltrexone on binding to CHO-mu receptor was observed by radioligand binding study.

RESULTS6 beta-naltrexol antagonized morphine analgesia but the potency was (6.1 +/- 1.7)% that of naltrexone. The effective duration of 6 beta-naltrexol was 3-4 times that of naltrexone and the peak time of the response was about 0.5-1 h after s.c. equivalent efficacy dose (ED95) in two models. Like naltrexone, 6 beta-naltrexol was effective by oral administration and the potency ratio of p.o./s.c. was 1/3. As an antagonist to opioid receptor, the displacement of 6 beta-naltrexol was about 12.5% that of naltrexone, which was almost in agreement with the efficacies against morphine analgesia in mouse.

CONCLUSIONCompared with naltrexone, 6 beta-naltrexol was less potent but duration was longer.

Analgesia ; Analgesics, Opioid ; antagonists & inhibitors ; Animals ; Female ; Male ; Mice ; Morphine ; antagonists & inhibitors ; Naltrexone ; analogs & derivatives ; pharmacology ; Narcotic Antagonists ; pharmacology ; Pain Threshold ; drug effects ; Receptors, Opioid, mu ; metabolism

PURPOSE: Nociceptin/orphanin FQ (N/OFQ) as an endogeneous hexadecapeptide is known to exert antinociceptive effects spinally. The aims of this study were to demonstrate the antinociceptive effects of i.t. N/OFQ and to investigate the possible interaction between N/OFQ and endogenous opioid systems using selective opioid receptor antagonists in rat formalin tests. MATERIALS AND METHODS: I.t. N/OFQ was injected in different doses (1-10 nmol) via a lumbar catheter prior to a 50 microL injection of 5% formalin into the right hindpaw of rats. Flinching responses were measured from 0-10 min (phase I, an initial acute state) and 11-60 min (phase II, a prolonged tonic state). To observe which opioid receptors are involved in the anti-nociceptive effect of i.t. N/OFQ in the rat-formalin tests, naltrindole (5-20 nmol), beta-funaltrexamine (1-10 nmol), and norbinaltorphimine (10 nmol), selective delta-, micro- and kappa-opioid receptor antagonists, respectively, were administered intrathecally 5 min after i.t. N/OFQ. RESULTS: I.t. N/OFQ attenuated the formalin-induced flinching responses in a dose-dependent manner in both phases I and II. I.t. administration of naltrindole and beta-funaltrexamine dose-dependently reversed the N/OFQ-induced attenuation of flinching responses in both phases; however, norbinaltorphimine did not. CONCLUSION: I.t. N/OFQ exerted an antinociceptive effect in both phases of the rat-formalin test through the nociceptin opioid peptide receptor. In addition, the results suggested that delta- and micro-opioid receptors, but not kappa-opioid receptors, are involved in the antinociceptive effects of N/OFQ in the spinal cord of rats.
Analgesics/administration & dosage/*pharmacology ; Animals ; Formaldehyde/toxicity ; Injections, Spinal ; Male ; Naltrexone/administration & dosage/analogs & derivatives/pharmacology ; Narcotic Antagonists/administration & dosage/*pharmacology ; Opioid Peptides/administration & dosage/*pharmacology ; Pain Measurement ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid/*agonists/drug effects

In the present study, whole-cell patch-clamp technique was used to observe the effects of SNC162, a selective agonist of δ-opioid receptors, on L-type Ca(2+) current (I(Ca-L)) and transient outward K(+) current (I(to)) in rat ventricular myocytes. The results showed that SNC162 significantly inhibited I(Ca-L) and I(to) in rat ventricular myocytes. The maximal inhibition rate of I(Ca-L) and I(to) reached (46.13±4.12)% and (36.53±10.57)%, respectively. SNC162 at 1×10(-4) mol/L inhibited the current density of I(Ca-L) from (8.98±0.40) pA/pF to (4.84±0.44) pA/pF (P<0.01, n=5) and inhibited that of I(to) from (18.69±2.42) pA/pF to (11.73±1.67) pA/pF (P<0.01, n=5). Furthermore, the effects of naltrindole, a highly selective antagonist of δ-opioid receptors, on I(Ca-L) and I(to) were also observed. The results showed that naltrindole alone had no effects on I(Ca-L) and I(to), while it abolished the inhibitory effects of SNC162 on I(Ca-L) and I(to). In conclusion, SNC162 concentration-dependently inhibited I(Ca-L) and I(to) in rat ventricular myocytes via activation of the δ-opioid receptors, which may be a fundamental mechanism underlying the antiarrhythmic effect of activating δ-opioid receptors.
Animals ; Anti-Arrhythmia Agents ; Benzamides ; pharmacology ; Calcium Channels, L-Type ; metabolism ; Cells, Cultured ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; drug effects ; metabolism ; Naltrexone ; analogs & derivatives ; pharmacology ; Patch-Clamp Techniques ; Piperazines ; pharmacology ; Potassium Channels ; metabolism ; Rats ; Receptors, Opioid, delta ; agonists

There is evidence that 5-7 d after acute seizure episodes induced by kainic acid (KA) the rats develop a long-lasting increase in the susceptibility to seizures followed by spontaneous recurrent seizures (SRS). The present study was focused on the role of hippocampal mu opioid receptors (MORs) in the susceptibility of rats to seizures with the KA model of epilepsy. The rats received a convulsant dose of KA (10 mg/kg, i.p.) were continuously infused with a selective MOR agonist PL017 (2.09, 2.59, 3.29 microg/microl), or a selective MOR antagonist beta-funaltrexamine hydrochloride (beta-FNA, 0.88, 1.10, and 1.35 microg/microl) into ventral hippocampus by means of mini-osmotic pumps. Seven days later, the susceptibility of rats to seizures was checked by a subconvulsant dose of KA (5 mg/kg, i.p.). PL017 infusion shortened the latency and increased the stage of seizures induced by subconvulsant dose of KA in a dose-dependent manner. In contrast, infusion of beta-FNA exhibited a dose-dependent effect against seizures challenged by subconvulsant dose of KA. These results indicate that hippocampal MOR may exert a promoting effect on the susceptibility of rats to KA-induced seizures.
Animals ; Disease Susceptibility ; Dynorphins ; pharmacology ; Epilepsy ; chemically induced ; physiopathology ; Hippocampus ; physiopathology ; Kainic Acid ; Male ; Naltrexone ; analogs & derivatives ; pharmacology ; Peptide Fragments ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, mu ; agonists ; antagonists & inhibitors ; physiology

The purpose of this study was to investigate the differences in subjective acute effects of alcohol and naltrexone among those who prefer spicy food to varying degrees. Acute biphasic alcohol effects scale (BAES), visual analogue scale for craving (VAS-C), blood alcohol concentration (BAC) and food preference scale were measured in 26 men. Repeated measures ANOVA (2 preference groupsx4 time blocks) on the stimulative subscale of BAES revealed a significant group by block interaction in naltrexone condition (N+) (P<0.001), but not in non-naltrexone condition (N-). Furthermore, repeated measures ANOVA (2 drug groupsx4 time blocks) on the stimulative subscale of BAES revealed a significant group by block interaction in strong preference for spicy food (SP) (P<0.001), but not in lesser preference for spicy food (LP). The paired t-test revealed that significant suppression of the stimulative subscale of BAES was observed at 15 min (P<0.001) and 30 min (P<0.001) after drinking when N+ compared with N- in SP. For those who prefer spicy food, the stimulative effect of acute alcohol administration was suppressed by naltrexone. This result suggests that the effect of naltrexone may vary according to spicy food preference.
Adult ; Alcohol Drinking/*adverse effects ; Alcoholism/*drug therapy ; Capsaicin/pharmacology ; Food Preferences/*drug effects ; Humans ; Male ; Naltrexone/adverse effects/*therapeutic use ; Narcotic Antagonists/adverse effects/*therapeutic use ; Questionnaires ; Sensory System Agents/pharmacology ; Young Adult

This work was performed to determine the role of delta-opioid receptor (DOR) in protection against acute ischemia/reperfusion injury. Transient (1 h) focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). DOR agonist TAN-67 (30 nmol, 60 nmol, 200 nmol), DOR antagonist naltrindole (20 nmol, 50 nmol, 100 nmol) or artificial cerebral spinal fluid (aCSF) was injected respectively into the lateral cerebroventricle of the rat 30 min before the induction of brain ischemia. Neurological deficits were assessed by the five-grade system (Longa's methods). The brain infarct was measured by cresyl violet (CV) staining and infarct volume was analyzed by an image processing and analysis system. The expression of DOR was detected by Western blot. The results showed that 60 nmol TAN-67 significantly reduced the infarct volume (P<0.05), attenuated neurological deficits (P<0.05) and tended to increase the expression of about 60 kDa DOR protein (P>0.05), while 100 nmol naltrindole aggravated ischemic damage and decreased about 60 kDa DOR protein expression (P<0.05). These results suggest that DOR activation protects the brain against acute ischemia/reperfusion injury in rat.
Animals ; Brain ; pathology ; Brain Ischemia ; drug therapy ; Infarction, Middle Cerebral Artery ; Injections, Intraventricular ; Naltrexone ; analogs & derivatives ; pharmacology ; Quinolines ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; agonists ; Reperfusion Injury

BACKGROUNDPreconditioning with repeated electroacupuncture (EA) could mimic ischemic preconditioning to induce cerebral ischemic tolerance in rats. The present study was designed to investigate whether mu (micro)-, delta (delta)- or kappa (kappa)-opioid receptors are involved in the neuroprotection induced by repeated EA preconditioning.

METHODSThe rats were pretreated with naltrindole (NTI), nor-binaltorphimine (nor-BNI) or D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), which is a highly selective delta-, kappa- or micro-opioid receptor antagonist respectively, before each EA preconditioning (30 minutes per day, 5 days). Twenty-four hours after the last EA treatment, the middle cerebral artery occlusion (MCAO) was induced for 120 minutes. The brain infarct volume was determined with 2, 3, 5-triphenyltetrazolium chloride staining at 24 hours after MCAO and compared with that in rats which only received EA preconditioning. In another experiment, the met-enkephalin-like immunoreactivity in rat brain was investigated by immunohistochemistry in both EA preconditioning and control rats.

RESULTSThe EA preconditioning reduced brain infarct volume compared with the control rats (P = 0.000). Administration of both NTI and CTOP attenuated the brain infarct volume reduction induced by EA preconditioning, presenting with larger infarct volume than that in the EA preconditioning rats (P < 0.001). But nor-BNI administration did not block the infarct volume reduction induced by EA preconditioning, presenting with smaller infarct volume than the control group rats (P = 0.000). The number of met-enkephalin-like immunoreactivity positive neurons in the EA preconditioning rats was more than that of the control rats (P = 0.000).

CONCLUSIONRepeated EA preconditioning stimulates the release of enkephalins, which may bind delta- and micro-opioid receptors to induce the tolerance against focal cerebral ischemia.

Animals ; Brain Ischemia ; prevention & control ; Electroacupuncture ; Enkephalin, Methionine ; analysis ; Immunohistochemistry ; Ischemic Preconditioning ; Male ; Naltrexone ; analogs & derivatives ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; physiology ; Receptors, Opioid, mu ; physiology ; Somatostatin ; analogs & derivatives ; pharmacology

The purpose of this study is to determine 1) whether morphine postconditiong (MPostC) can attenuate the intercellular adhesion molecules-1 (ICAM-1) expression after reoxygenation injury and 2) the subtype(s) of the opioid receptors (ORs) that are involved with MPostC. Human umbilical vein endothelial cells (HUVECs) were subjected to 6 hr anoxia followed by 12 hr reoxygenation. Three morphine concentrations (0.3, 3, 30 microM) were used to evaluate the protective effect of MPostC. We also investigated blockading the OR subtypes' effects on MPostC by using three antagonists (a micro-OR antagonist naloxone, a kappa-OR antagonist nor-binaltorphimine, and a delta-OR antagonist naltrindole) and the inhibitor of protein kinase C (PKC) chelerythrine. As results, the ICAM-1 expression was significantly reduced in the MPostC (3, 30 microM) groups compared to the control group at 1, 6, 9, and 12 hours reoxygenation time. As a consequence, neutrophil adhesion was also decreased after MPostC. These effects were abolished by coadministering chelerythrine, nor-binaltorphimine or naltrindole, but not with naloxone. In conclusion, it is assumed that MPostC could attenuate the expression of ICAM-1 on endothelial cells during reoxygenation via the kappa and delta-OR (opioid receptor)-specific pathway, and this also involves a PKC-dependent pathway.
Animals ; Benzophenanthridines/pharmacology ; Endothelial Cells/cytology/*drug effects/*metabolism ; Endothelium, Vascular/cytology ; Humans ; Intercellular Adhesion Molecule-1/genetics/*metabolism ; Morphine/*pharmacology ; Naloxone/pharmacology ; Naltrexone/analogs & derivatives/pharmacology ; Narcotic Antagonists/pharmacology ; Narcotics/*pharmacology ; Protein Isoforms/metabolism ; Protein Kinase C/antagonists & inhibitors/metabolism ; Receptors, Opioid/metabolism ; Reperfusion Injury/*metabolism ; Signal Transduction/physiology ; Umbilical Veins/cytology

OBJECTIVETo investigate the effect of DADLE, a δ-opioid receptor agonist, on the proliferation of human liver cancer HepG2 cells and explore the mechanism involving PKC pathway.

METHODSHepG2 cells were treated with DADLE at different doses (0.01, 0.1, 1.0 and 10 µmol/L). Cell viability was determined using methyl thiazolyl terazolium (MTT) assay. The expression of PKC mRNA and p-PKC protein were examined by RT-PCR and Western blot assay. After treated separately with DADLE plusing NAL or PMA, the cell cycle of HepG2 cells was analyzed by flow cytometer. MTT was used to detect their proliferation capacity and Western blot was used to examine the p-PKC expression. The growth inhibitory rate of HepG2 cells treated with DADLE and cis-diammine dichloridoplatinum (CDDP) was analyzed.

RESULTSDADLE at different concentrations showed an inhibitory effect on the proliferation of HepG2 cells though inhibiting the expression of PKC mRNA and p-PKC protein. The results of flow cytometry showed that compared with the control group, the percentage of S + G(2)/M cells in DADLE-treated group was lowered by 3.94% (P < 0.01). Meanwhile, after treated with NAL and PMA, the percentage was elevated by 3.22% and 3.63%, respectively (P < 0.01). The MTT and Western blot assays showed that compared with the control group, the values of A570 and p-PKC protein levels in the HepG2 cells of DADLE-treated group were significantly decreased (P < 0.01). After treatment with NAL and PMA, the values of A570 and p-PKC protein levels were elevated significantly (P < 0.01). The growth inhibitory rate of DADLE + CDDP group was 79.9%, significantly lower than 25.2% and 43.2% of the DADLE and CDDP groups, respectively.

CONCLUSIONSActivation of δ-opioid receptor by DADLE inhibits the apoptosis of human liver cancer HepG2 cells. The underlying mechanism may be correlated with PKC pathway. DADLE can enhance the chemosensitivity of HepG2 cells to CDDP.

Antineoplastic Agents ; pharmacology ; Cell Cycle ; drug effects ; Cell Proliferation ; drug effects ; Cisplatin ; pharmacology ; Dose-Response Relationship, Drug ; Drug Resistance, Neoplasm ; Enkephalin, Leucine-2-Alanine ; administration & dosage ; pharmacology ; Hep G2 Cells ; Humans ; Naltrexone ; analogs & derivatives ; pharmacology ; Phosphorylation ; Protein Kinase C ; genetics ; metabolism ; RNA, Messenger ; metabolism ; Receptors, Opioid, delta ; agonists ; Signal Transduction ; Tetradecanoylphorbol Acetate ; analogs & derivatives ; pharmacology

OBJECTIVETo investigate the dual effects by the delta opioid receptor agonists DPDPE on the delayed rectified potassium channels in NG108-15 cells.

METHODSA series of outward currents were evoked in NG108-15 cells by depolarizing voltage from -50 mV to +80 mV at holding potential of -90 mV. These currents were delayed rectified potassium currents. Relatively selected delta opioid receptor agonists DPDPE of higher and lower concentrations were used to modulate the delayed rectified K+ current in NG108-15 cells. Opioid receptor antagonist Naloxone (NAL) and relatively selected delta opioid receptor antagonist Naltrindole (NTI) were used in the present experiments for the characterization of the actions of opioid receptors.

RESULTSThe relatively higher concentrations of delta opioid receptor agonist DPDPE (> or = 10(-6) mol/L) significantly increased the amplitude of the delayed rectified K+ current. On the contrary, the relatively lower concentrations of DPDPE (< or = 10(-12) mol/L) decreased the amplitude of the delayed rectified K+ current (P < 0.05). Furthermore both the increase and decrease were time-dependent.

CONCLUSIONSdelta opioid receptor agonist has dual regulatory effects on the delayed rectified potassium channels in NG108-15 cells.

Animals ; Cell Membrane ; metabolism ; Enkephalin, D-Penicillamine (2,5)- ; pharmacology ; Glioma ; metabolism ; pathology ; Hybrid Cells ; metabolism ; Mice ; Naloxone ; pharmacology ; Naltrexone ; analogs & derivatives ; pharmacology ; Neuroblastoma ; metabolism ; pathology ; Patch-Clamp Techniques ; Potassium Channels, Inwardly Rectifying ; drug effects ; metabolism ; Rats ; Receptors, Opioid, delta ; agonists ; Tumor Cells, Cultured