Delta Opiate Receptors Research Articles

Lymphflow stimulation in microvessels of lung peptides in acute lung edema

Introduction . The relevance of the problem of high mortality in acute lung edema (ALE) is associated with the insufficient effectiveness of treatment methods for extreme rapidly occurring lung pathology. The goal is a comprehensive study of the role of lymph flow stimulation using a lymph-stimulating peptide in the pathogenesis of ALE under conditions of lung biomicroscopy. Materials and methods . Biomicroscopy of the lungs using an implanted chamber and mesentery of the rat small intestine, laser Doppler lung flowmetry, morphological and histological examination of the lungs. Registration of contractile activity of the wall, valves of the lymphatic microvessels of the mesentery by photometry and the rate of lymph flow; determination of the diameter of microvessels, solids and pulmonary coefficient in the lungs. photo and video registration of the lungs. Results . The direct peptidic lymphostimulant caused activation of lymphatic flow in the lymphatic microvessels of the mesentery and lungs in patients with ALE, followed by restoration of microcirculation in the lungs. The reduction and elimination of edema of the interstitial space in the lungs was associated with the restoration of the diameter of the lymphatic and venous microvessels. Prophylactic use of the peptide was accompanied by an increase in animal survival by 3 times. The use of the peptide after the ALE did not affect survival, however, it increased the life expectancy of rapidly dying animals during the first 10 min up to a day from 16 to 46 %. Conclusions . Activation of motility of the lymphatic microvessels and lymph flow in ALE with the help of a peptidic lymphostimulator, an agonist of the delta opiate receptors, helps to eliminate edema as a result of removing excess interstitial fluid through the lymphatic vessels of the lungs to the main venous collectors and then to the right atrium, than reduces the load on the left half of the heart with cardiogenic ALE. The restoration of microlymph- and microhemocirculation in the lungs contributed to the restoration of the structure of the lung tissue and a 3-fold increase in the survival and longevity of animals. Activation of the lymphatic system is an effective, but unused reserve of the body playing an important role in the pathogenesis of ALE.

Trimebutine: a state-of-the-art review.

Trimebutine maleate has been used extensively, since the late 1960's, for the treatment of functional gastrointestinal disorders, including irritable bowel syndrome (IBS). It is usually linked to the antispasmodic class of agents, but its properties make trimebutine an unmatched and multi-tasking compound. The efficacy on relieving abdominal pain has been demonstrated in various clinical studies with different protocols of treatment. The main effect was first believed to be merely due to its antispastic activity, but further evidences expanded the acknowledgement of a broader impact on the gastrointestinal tract. The actions of trimebutine are mediated via an agonist effect on peripheral mu, kappa and delta opiate receptors and a modulation of gastrointestinal peptides release. The final motor effects on the gut are summarized in an acceleration of the gastric emptying, an induction of premature phase III of the migrating motor complex in the small intestine and a modulation of the contractile activity of the colon. Moreover, it has been shown to have a role in regulating the visceral sensitivity. It has been observed that this drug is also a multiple-ion channel modulator in the gut. Its function at various levels, from motility to pain control, makes this drug unique and its spectrum of action can be exploited for the treatment of both hypermotility and hypomotility disorders including irritable bowel syndrome and other functional gastrointestinal diseases. This article provides an overview of the current knowledge on the pharmacological mechanisms of trimebutine and its clinical applications in gastrointestinal disorders. Its biochemical properties and the complex mechanisms of action, along with a well-studied pharmacological safety, make this compound still actual and valuable.

Serotonin syndrome due to fluoxetine and tramadol in renal impaired patient

Serotonin syndrome causes confusion or altered mental status; other symptoms include myoclonus, shivering, tremors, diaphoresis, hyperreflexia, incoordination, fever and diarrhoea. Tramadol possesses dual pharmacological effects i.e., a weak opiate agonist at mu, kappa and delta opiate receptors along with reuptake inhibition of norepinephrine and serotonin. Risk associated with tramadol increases when co-administered with serotonergic antidepressants or MAOIs (monoamine oxidase inhibitors) and in renal impaired. The incidence of this syndrome is less than 1% as most of the cases remain unreported. The case highlights the fact that interaction between serotonergic agents like fluoxetine and tramadol especially in the presence of co-morbid medical illness can lead to serotonin syndrome.

Discovery and pharmacological characterization of a selective delta opiate receptor antagonist (CP-646,777)

CP-646,777 (compound 2a) is identified as a potent and selective delta opioid receptor antagonist. The synthesis, pharmacological evaluation, disposition characteristics and pharmacokinetic properties of this compound are reported herein. An approach for reducing clearance as measured by human liver microsomes is demonstrated. The significance of p-glycoprotein efflux on CNS disposition and on the pharmacological action of CP-646,777 is also discussed.

Neonatal injury alters adult pain sensitivity by increasing opioid tone in the periaqueductal gray

Studies in both rodents and humans have shown that acute inflammatory pain experienced during the perinatal period produces long-term decreases in pain sensitivity (hypoalgesia) (Grunau et al., 1994a, 2001; Ren et al., 2004; LaPrairie and Murphy, 2007). To date, the mechanisms underlying these long-term adaptations, however, have yet to be elucidated. The present studies tested the hypothesis that neonatal inflammatory pain induces an upregulation in endogenous opioid tone that is maintained into adulthood, and that this increase in opioid tone provides the underlying mechanism for the observed hypoalgesia. On the day of birth (P0), inflammatory pain was induced in male and female Sprague-Dawley rats by intraplantar administration of carrageenan (CGN; 1%). In adulthood (P60), these animals displayed significantly increased paw withdrawal latencies in response to a noxious thermal stimulus in comparison to controls. Systemic administration of the brain-penetrant opioid receptor antagonist naloxone HCl, but not the peripherally restricted naloxone methiodide, significantly attenuated the injury-induced hypoalgesia. Direct administration of naloxone HCl or antagonists directed at the mu or delta opioid receptors into the midbrain periaqueductal gray (PAG) also significantly reversed the injury-induced hypoalgesia in adult rats. Parallel anatomical studies revealed that inflammatory pain experienced on the day of birth significantly increased beta-endorphin and met/leu-enkephalin protein levels and decreased opioid receptor expression in the PAG of the adult rat. Thus, early noxious insult produces long-lasting alterations in endogenous opioid tone, thereby profoundly impacting nociceptive responsiveness in adulthood.

Evaluation of the mu and kappa opioid actions of butorphanol in humans through differential naltrexone blockade.

Butorphanol exerts activity at mu, kappa, and delta opiate receptors in rats and monkeys but produces predominant mu-like effects in humans. The aim of this study was to determine if the kappa receptor-mediated actions of butorphanol could be unmasked or enhanced by giving it in combination with naltrexone, an opioid antagonist with higher affinity for mu vs kappa receptors. Ten healthy adult inpatient volunteers (eight men, two women), with opioid abuse histories, completed this double-blind, randomized, placebo-controlled study. Naltrexone (0, 1, 3, 10, or 30 mg, p.o.) was administered 1 h before butorphanol (0, 6, or 12 mg/70 kg, i.m.) during 15 test sessions. An array of physiological (e.g., vital signs, urine output, and subject- and observer-rated) measures was collected before and for 4 h after drug administration. Naltrexone alone produced no direct effects. Butorphanol alone produced typical mu-, but not kappa-, related physiological effects (e.g., miosis, respiratory depression) and produced mood and drug effects considered typical of both mu (e.g., "liking," "good drug effects") and kappa agonists (e.g., increases in perceptual disturbances). Naltrexone pretreatment led to significant butorphanol-induced diuresis (i.e., increased urine output and decreased urine osmolality). Naltrexone generally produced a dose-dependent blockade of subjective responses. These data suggest that naltrexone antagonism unveiled the kappaergic activity of butorphanol as measured by diuresis, while subjective responses generally attributed to mu vs kappa receptors were not dissociable. Moreover, these data demonstrate that butorphanol exerts physiologically relevant kappa agonist activity at these supraanalgesic doses in humans.

Role of hepatic opioid receptors in the regulation of bile excretion

Experiments on isolated rat liver perfused with Ringer-Krebs bicarbonate buffer showed that stimulation of delta-opiate receptors in this organ increases bile flow rate and taurocholate secretion. Stimulation of micro-opiate receptors decelerated bile production and inhibited taurocholate secretion. Acceleration of bile production and stimulation of taurocholate secretion under the influence of dalargin is probably related to its interaction with delta-opiate receptors in the liver.

Regulation of pancreatic secretion in vitro by nociceptin/orphanin FQ and opioid receptors: A comparative study

The effects of nociceptin/orphanin FQ (N/OFQ) on gastrointestinal functions resemble those of classic analgesic opioid agonists. In this study, we compared changes in amylase release from guinea pig isolated pancreatic acini and lobules induced by the N/OFQ analogue [Arg 14,Lys 15]N/OFQ and by the delta-receptor opioid agonist deltorphin. Carbachol strongly stimulated amylase release from isolated acini. Both peptides left baseline and carbachol-stimulated amylase secretion from pancreatic acini unchanged. Co-incubation of KCl-stimulated lobules with [Arg 14,Lys 15]N/OFQ or deltorphin inhibited KCl-induced amylase release in a concentration-dependent manner. Although maximal inhibition of amylase release by [Arg 14,Lys 15]N/OFQ and deltorphin had similar amplitude, [Arg 14,Lys 15]N/OFQ was 100-fold more potent than deltorphin on a molar basis. The selective NOP-receptor antagonist [Nphe 1,Arg 14,Lys 15]N/OFQ-NH 2 (UFP-101) antagonized [Arg 14,Lys 15]N/OFQ-induced inhibition but left deltorphin-induced inhibition unchanged. The selective delta opiate receptor antagonist naltrindole had no effect on [Arg 14,Lys 15]N/OFQ inhibition but partly prevented the inhibition by deltorphin. [Arg 14,Lys 15]N/OFQ and deltorphin combined had no influence on each other. These findings show that [Arg 14,Lys 15]N/OFQ inhibits pancreatic enzyme secretion by suppressing cholinergic transmission in intralobular nerve fibers, as previously reported for opioid agents. They suggest that [Arg 14,Lys 15]N/OFQ inhibition of amylase release is mediated through the NOP receptor and not through the delta opioid receptor. The N/OFQ-NOP receptor system, like the delta opioid system, plays an inhibitory role in regulating exocrine pancreatic secretion.

Specific changes in levels of autoantibodies to glutamate and opiate receptors induced by morphine administration in rats

Several groups of brain receptors are involved in the mechanisms underlying the development of opiate addiction, but the interactions occurring between these neuroreceptors and the immune system, including potential autoimmune responses, remain poorly understood. We studied in rats the effects of repeated administration of different psychotropic drugs on serum levels of autoantibodies (aAbs) to the mu delta-opiate receptor (MDOR), as well as to the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) GluR1 and to the N-methyl- d-aspartate (NMDA) NR2 subunits of the glutamate receptor, as analyzed by ELISA. We found that repeated administration of morphine significantly elevated aAbs levels to MDOR and to the AMPA GluR1 subunit, but not to the NMDA NR2 subunit. In contrast, a similar regimen of a psychostimulant drug, such as d-amphetamine, or a commonly abused substance, such as nicotine, had no effect on these aAbs levels. A nonspecific elevating effect on aAbs to the brain structural protein S100B was observed for all drugs tested versus controls. These observations support the hypothesis that, following opiate administration, specific interactions between nervous and immune systems occur. Therefore, together with further investigations on their potential functional consequences, we propose a thorough exploration of aAbs to MDOR and to AMPA GluR1 subunit as early biomarkers signaling opiate addiction.

Cocaine and heroin (‘speedball’) self-administration: the involvement of nucleus accumbens dopamine and μ-opiate, but not δ-opiate receptors

The combined administration of heroin and cocaine ('speedball') is common among intravenous drug users. Dopamine receptors in the nucleus accumbens play a key role in cocaine self-administration; however, their role in speedball self-administration is unknown, as is the role of opiate receptors in this region. The effect of blocking dopamine D1, D2, mu-opiate or delta-opiate receptors in the nucleus accumbens on the intravenous self-administration of combined heroin and cocaine was examined in rats. Rats with bilateral cannulae implanted into the nucleus accumbens were trained to self-administer intravenous speedball (ratio of cocaine/heroin, 17:1) under a progressive ratio (PR) schedule. Prior to their self-administration session, rats were then microinjected with the dopamine D1 receptor antagonist SCH 23390 (1 and 6 nmol side(-1)), the D2 receptor antagonist raclopride (3 and 10 nmol side(-1)), the mu-opiate receptor antagonist CTOP (0.1, 0.3 and 1.0 nmol side(-1)), the delta-opiate receptor antagonist naltrindole (1.0, 3.0 and 10 nmol side(-1)) or a cocktail of SCH 23390 (1 nmol side(-1)) and CTOP (0.1 nmol side(-1)) into the nucleus accumbens. Microinjection of SCH 23390, raclopride or CTOP into the nucleus accumbens produced dose-dependent decreases in breakpoints under the PR schedule, while naltrindole was without effect. The highest dose of SCH 23390 also significantly reduced locomotor activity measured during speedball self-administration. The combination of SCH 23390 and CTOP significantly reduced breakpoints, while not affecting locomotor activity. These results indicate that dopamine and mu-opiate receptors, but not delta-opiate receptors, in the nucleus accumbens are involved in the reinforcing effects of speedball. Combined administration of D1 and mu-opiate receptor antagonists may be more selective at reducing the reinforcing effects of speedball self-administration than either drug alone.

INTERACTIONS BETWEEN δ OPIOID RECEPTORS AND α2A‐ADRENOCEPTORS

1. Several studies have reported functional interactions between different subtypes of opioid and alpha2A-adrenoceptors in the induction of spinal cord analgesia. The mechanisms underlying this phenomenon are not well characterized. We propose that direct receptor-receptor associations could account for some of the observed functional interactions. In the present study, we examined the presence of delta opioid receptors and alpha2A-adrenoceptors in interacting complexes and the functional implications of such interactions on receptor activity. 2. Using the proximity based bioluminescence resonance energy transfer (BRET) assay, we found that the delta opioid receptors and alpha2A-adrenoceptors are in close enough proximity (< 100 A) in live cells that can foster physical interactions. 3. Using coimmunoprecipitation of differentially epitope-tagged receptors, we found that delta opiate receptors exist in interacting complexes with alpha2A-adrenoceptors in heterologous cells. 4. Finally, using receptor activity mediated neurite outgrowth in Neuro 2A cells as a physiological readout, we found that interactions between delta opiate receptors and alpha2A-adrenoceptors have functional consequences. The expression of alpha2A-adrenoceptors is sufficient to promote delta opiate receptor-mediated neurite outgrowth, suggesting that the presence of inactive alpha2A-adrenoceptors can enhance delta opiate receptor-mediated signalling. 5. Taken together, these findings suggest that modulation of receptor function as a result of physical associations between delta opiate receptors and alpha2A-adrenoceptors may account for the observed synergy between opiate and adrenergic agonists in spinal analgesia.

The Effects of Rotation Stress on Measures of Immunity. The Role of Opiate Receptors

Experiments were performed on mongrel male rats to study the effects of blockade of delta, mu, and kappa opiate receptors on antibody formation, delayed-type hypersensitivity (DTH), and changes in the numbers of antibody-forming cells (AFC) and nucleated cells in the lymph nodes and spleen in a local form of immune response in a model of rotation stress. These studies showed that rotation stress led to mild suppression of immune inflammation in DTH, significant increases in the numbers of AFC and nucleated cells in regional lymph nodes, but no change in the peripheral blood antibody titer. Blockade of delta, mu, and kappa opiate receptors with naloxone altered these stress-induced effects. It is suggested that abolition of the stimulating effect of rotation stress on the number of AFC and depression of DTH may be associated with blockade of the effects of beta-endorphin and met-enkephalin, which act predominantly via stimulation of delta receptors.

Possible role of the phosphoinositide pathway for signal transduction in changes in the sensitivity of delta-opiate receptors during diabetes mellitus.

We studied the effects of selective delta-opiate receptor agonists and antagonists on the phosphoinositide pathway in lymphocytes from healthy donors and patients with diabetes mellitus. The test compounds probably play a role in changes in the sensitivity to pharmacological substances binding to delta-opiate receptors during diabetes mellitus.

Effect of opiate peptide dalargin and des-Tyr-dalargin on cardiac pump function during ischemia-reperfusion.

Experiments on isolated perfused rat heart showed that nonselective micro- and delta-opiate receptor agonist dalargin decreased contractility of the intact heart, but had no effect on pump function of the ischemic myocardium. Dalargin analogue des-Tyr-dalargin not binding to opiate receptors decreased contractility of intact myocardium and isolated heart exposed to 45-min total ischemia. We hypothesize that the influence of dalargin is related to activation of cardiac delta-opiate receptors, while the inotropic effect of des-Tyr-dalargin is mediated by other receptors.

Down-regulation of 3H-lofentanil binding to opiate receptors in different cultured neuronal cells

There was stereospecific binding of 3H-lofentanil (KD value = 1.53 nM) to membranes of neuroblastoma-glioma NG 108-15 cells which are known to bear high affinity binding sites for enkephalin derivatives (delta-opiate receptor subtype). There was no high affinity specific binding of the mu-opiate specific ligand 3H-sufentanil. The specific binding of 3H-lofentanil to delta-opiate receptor subtype was down-regulated (decrease in Bmax value without change in the KD value) after prolonged incubation of the cells in the presence of leu- and met- enkephalin (0.1 microM). There was no down-regulation of the opiate receptors (3H-lofentanil and 3H-D-ala-D-leu-enkephalin specific binding) after incubation of NG 108-15 cells with drugs from the fentanyl series (alfentanil or sufentanil). In cultured neurones from rat forebrain (15 day old embryos), the 3H-lofentanil binding was specific with high affinity (KD: 0.048 nM) and a slow dissociation rate similar to that in adult rat cortex. Drugs of the fentanyl series (4-anilino-piperidines) were potent displacers whereas agonists of the delta- (enkephalin derivatives), sigma- (phencyclidine, haloperidol, 3-hydroxyphenyl-propylpiperidine) or K- (U 50488) opiate sites had a low affinity (Ki greater than 0.5 microM) for 3H-lofentanil specific binding sites. Since there was also specific binding of 3H-sufentanil, the opiate receptors in cultured neurones seem to be mainly of the mu-subtype and this is consistent with the ontogeny of opiate receptors subtypes. These receptors were down-regulated after incubation in the presence of etorphine, sufentanil and alfentanil but not enkephalin derivatives.(ABSTRACT TRUNCATED AT 250 WORDS)

Endomorphins exit the brain by a saturable efflux system at the basolateral surface of cerebral endothelial cells

Endomorphin-1 (EM-1) and endomorphin-2 (EM-2) are two highly selective mu-opiate receptor agonists. We recently demonstrated that EM-1 and EM-2 have a saturable transport system from brain-to-blood in vivo. Since the endothelial cells are the main component of the non-fenestrated microvessels of the blood-brain barrier (BBB), we examined whether these endogenous tetrapeptides have a saturable transport system in cultured cerebral endothelial cells. EM-1 and EM-2 binding and transport were studied in a transwell system in which primary mouse endothelial cells were co-cultured with rat glioma cells. We found that binding of both endomorphins was greater on the basolateral than the apical cell surface. Flux of EM-1 and EM-2 occurred predominantly in the basolateral to apical direction, each showing self-inhibition with an excess of the respective endomorphin. Transport was not influenced by the addition of the P-glycoprotein inhibitor, cyclosporin A. Neither the mu-opiate receptor agonist DAMGO nor the delta-opiate receptor agonist DPDPE had any effect on the transport. Thus, the results show that a saturable transport system for EM-1 and EM-2 occurs at the level of endothelial cells of the BBB, and unlike beta-endorphin and morphine, P-glycoprotein is not needed for the brain-to-blood transport. Cross-inhibition of the transport of each endomorphin by the other suggests a shared transport system that is different from mu- or delta-opiate receptors. As endormorphins are mainly produced in the CNS, the presence of the efflux system at the BBB could play an important role in pain modulation and neuroendocrine control.

Heparan sulfate proteoglycans are involved in opiate receptor-mediated cell migration.

Opioid receptors are expressed in cells of the immune system, and potent immunomodulatory effects of their natural and synthetic ligands have been reported. In some studies, the opiate receptor antagonist naloxone itself displayed immunomodulatory actions. We investigated effects of naloxone on leukocyte chemotaxis. Cell migration was tested in micropore filter assays using modified Boyden chambers, and receptor expression was investigated using radiolabel binding assays. Naloxone induced peripheral blood nonadherent mononuclear cell and neutrophil chemotaxis at nanomolar concentrations and deactivated their migration toward beta-endorphin, angiotensin II, somatostatin, or interleukin-8 but not toward RANTES, vasoactive intestinal peptide, or substance P. Ligand binding studies showed no alteration in the binding of interleukin-8 to neutrophils by naloxone. Cleavage of heparan sulfate from proteoglycans on the cells' surface completely inhibited chemotactic and deactivating properties of naloxone but not other attractants. Chemotactic properties were abolished by pretreating cells with heparinase, chondroitinase, sodium chlorate, and anti-syndecan-4 antibodies, indicating the involvement of syndecan-4. The extent of migration toward naloxone was diminished by pretreatment with dimethylsphingosine, a specific sphingosine kinase inhibitor. As syndecan-4 signaling in leukocyte chemotaxis involves activation of sphingosine kinase, results indicate that naloxone interacts with syndecan-4 function in cell migration and suggest a role for heparan sulfate proteoglycans as coreceptors to members of the delta-opiate receptor family.

Role of Opiate Receptors and ATP-Dependent Potassium Channels of Mitochondria in the Formation of Myocardial Adaptive Resistance to the Arrhythmogenic Effect of Ischemia and Reperfusion

Preliminary stimulation of opiate receptors (ORs) by intravenous administration of mu agonist DALDA (0.5 mg/kg), delta 1 agonist DPDPE (0.5 mg/kg), and kappa agonist (-)-U-50.488 (1 mg/kg) increases rat myocardial resistance to arrhythmogenic effect of coronary occlusion (10 min) and reperfusion (10 min). Activation of delta 2 ORs (DSLET, 0.5 mg/kg) has no effect on the incidence rate of ischemic and reperfusion arrhythmias. Preliminary administration of glibenclamide (0.3 mg/kg), an inhibitor of KATP channels, blocks the antiarrhythmic effect of DALDA and DPDPE. Repeated short-term exposures of rats to immobilization within two weeks increases the heart tolerance to the arrhythmogenic effect of coronary occlusion and reperfusion. This effect disappears after administration of CTAP (0.5 mg/kg), a mu antagonist, or injection of 5-hydroxydecanoate (5 mg/kg), an inhibitor of mitochondrial KATP channels. The selective antagonists of delta and kappa ORs have no effect on cardiac adaptation-induced resistance to the arrhythmogenic effect of ischemia and reperfusion. We believe that stimulation of mu, delta, and kappa ORs increases myocardial tolerance to the arrhythmogenic effect of ischemia and reperfusion through activation of KATP channels. The antiarrhythmic effect of the adaptation is mediated by stimulation of mu ORs and mitochondrial KATP channels.

Stimulation of mu and delta-Opiate Receptors and Tolerance of Isolated Heart to Oxidative Stress: the Role of NO-Synthase.

Preliminary intravenous injection of delta-opiate receptor (OR) agonists DSLET (0.1 mg/kg) or DTLET (0.1 mg/kg) increased tolerance of isolated perfused myocardium to damage by oxidative stress simulated in vivo with FeSO4 + ascorbic acid. This manifested itself by a decreased level of creatine phosphokinase (CPK) in the perfusate flowing out of the heart during the oxidative exposure. The preliminary systemic injection of mu-agonists DAMGO (0.1 mg/kg) or DALDA (0.1 mg/kg) failed to affect the release of CPK from the myocardium. The cardioprotective effect of the delta-agonist DSLET was completely abolished by preliminary intravenous injection of the delta-OR antagonist ICI 174,864 (2.5 mg/kg). The intravenous injection of the NO-synthase inhibitor L-NAME (50 mg/kg) also completely abolished the cardioprotective effect of delta-OR stimulation. The preliminary injection of DSLET but not of DAMGO prevented an increase in the level of diene conjugates and a decrease in the activity of superoxide dismutase (SOD) in the isolated myocardium tissue. Thus, the in vivo stimulation of delta-OR increased the tolerance of the heart to oxidative stress through activation of NO-synthase and SOD.

Acute ethanol treatment modulates delta opioid receptors in N18TG2 cells.

The in vitro adaptive responses of delta opiate receptors (DOR) to chronic ethanol treatment have been well documented. The acute effects of ethanol on these receptors are not well characterized beyond its effect on ligand binding. The aim of this study was to evaluate the acute effects of clinically relevant concentrations of ethanol (50-200 mm) on the saturation binding kinetics, receptor/ligand internalization, and agonist stimulation of G-protein coupling in N18TG2 cells expressing the Flag epitope-tagged mouse DOR. Confocal microscopy was used to localize Flag epitope-tagged DOR in N18TG2 cells. Saturation binding assays at 4 degrees C and 37 degrees C were conducted in the absence or presence of ethanol on cells not pretreated or pretreated with ethanol for 30 min at 37 degrees C. Highly specific delta agonist, DPDPE ([D-Pen2,D-Pen5]enkephalin), was used in these studies. The effect of ethanol on agonist stimulation of G-protein coupling was examined using [35S]GTPgammaS (guanosine-5'-O-(3-thio)triphosphate) binding to membranes. Agonist-mediated receptor internalization was examined using flow cytometry of cells labeled with the antiserum directed against the Flag epitope, and the ligand internalization was examined using [3H]DPDPE. Ethanol decreased the binding of the agonist [3H]DPDPE, and not the antagonist [3H]diprenorphine, in a dose-dependent manner. These effects were temperature-dependent. Ethanol reversibly inhibited agonist stimulation of [35S]GTPgammaS binding. In non-pretreated cells, ethanol decreased the rate of receptor/ligand internalization, but this effect was not seen in ethanol pretreated cells. Taken together, these results suggest that pretreatment of N18TG2 cells with ethanol induces compensatory mechanisms that allow the receptor to function efficiently in its presence. Acute ethanol decreased the binding, agonist-mediated functional coupling and receptor/ligand internalization in N18TG2 cells expressing epitope-tagged DOR. In these cells, 30-min pretreatment with ethanol was sufficient to reverse these effects.