Addition Of Naloxone Research Articles

Laxative Use in Inpatients on Oxycodone/Naloxone Prolonged Release and Oxycodone Prolonged Release for Cancer and Non-cancer Pain

Objective: To examine the laxative prescriptions in hospital inpatients with cancer and non-cancer pain on oxycodone compared to oxycodone plus naloxone combination.Design: Retrospective case note review.Setting: A palliative care inpatient unit and a general medical ward in a large tertiary referral hospital.Participants: Eighty-four patients receiving oxycodone or combination oxycodone/naloxone on general medical (45 patients) and palliative care wards (39 patients).Main outcome measures: The primary recorded outcomes were regular opioid dose (milligrams per day) and number of prescribed laxatives (type, doses, and frequency per day).Results: Sixty-three (75%) patients in the study were on at least one laxative. In the general medicine inpatients, those on combined oxycodone/naloxone received on average 3.7 laxative doses per day compared to the oxycodone patients receiving 1.6 doses a day. In the palliative medicine population, both groups received a similar number of laxatives, despite the oxycodone/naloxone patients being on lower opioid doses.Conclusion: This retrospective study of hospital inpatients with cancer and non-cancer pain found that laxative use was not reduced in those on combined oxycodone/naloxone compared to oxycodone alone, suggesting that despite the interpretations of the clinical trials in the phase IV setting, the addition of naloxone had no effect on reducing laxative use.

Epicatechin's cardiovascular protective effects are mediated via opioid receptors and nitric oxide.

Cardiovascular disease is the leading cause of mortality globally. Epicatechin has previously been shown to improve vascular responses and possess cardioprotective properties. However, the mechanisms underpinning these cardiotropic outcomes remain unknown. The aim of this study was to further identify epicatechin's mechanism of action in the cardiovasculature. The effects of epicatechin on isolated rat conduit arteries, resistance vessels and cardiac electrophysiology were investigated on resting tension and precontracted vessels and cardiac action potential parameters, both in the presence and in the absence of various antagonists. At resting tension, epicatechin alone did not affect the vasoreactivity of either conduit or resistance vessels. In noradrenaline pre-contracted thoracic aortic arteries and potassium chloride pre-contracted mesenteric vessels, epicatechin (10-9-10-4M) induced significant vasorelaxation. The addition of naloxone (10-5M), NG-nitro-L-arginine methyl ester (10-5M), 4-aminopyridine (5mM) and verapamil (10-5M) attenuated epicatechin-mediated vasorelaxation. No change in epicatechin-mediated vasorelaxation was observed with the addition of atropine (10-5M). Epicatechin significantly improved cardiac electrophysiology by reducing the resting membrane potential, action potential amplitude and force of contraction that was mitigated following the addition of naloxone (10-5M). Epicatechin significantly decreased the action potential duration at 20, 50 and 90% duration and time to 90% relaxation of force that was unchanged following the addition of naloxone (10-5M). These findings suggest epicatechin's vascular responses and cardioprotective effects are mediated through opioid receptors, nitric oxide, potassium channel and calcium channel activation and highlight the importance of the endothelium/nitric oxide in epicatechin mediated vasorelaxation.

Buprenorphine alone or with naloxone: Which is safer?

To address concerns regarding the intravenous diversion of buprenorphine, a combined buprenorphine-naloxone (BUP-NLX) preparation was developed. The aim of this study is to compare health outcomes in opioid dependent patients treated with BUP and BUP-NLX. All patients treated with BUP and/or BUP-NLX in Western Australia between 2001 and 2010 were included in the study ( N = 3455). Patients were identified via State prescribing records and matched against the State mortality, hospital, and emergency department records. Rates of health events were examined and compared using Cox Proportional Hazard Models and Generalized Estimating Equations. While on treatment there was no significant difference between mortality rates in the two groups, mortality rates following the cessation of treatment were significantly higher in patients treated with BUP-NLX (adjusted hazard ratio: 1.59). Rates of hospitalization were significantly elevated in BUP-NLX patients (adjusted odds ratio: 1.17) compared with BUP treated patients; however, rates of hospitalization with a skin/subcutaneous diagnosis were significantly lower in BUP-NLX treated patients (adjusted odds ratio: 0.65). Off-treatment rates of both all-cause hospital admissions (adjusted odds ratio: 1.53) and hospital admissions with an opioid poisoning diagnosis (adjusted odds ratio: 1.59) were significantly elevated in BUP-NLX treated patients compared with BUP treated patients. The addition of naloxone does not appear to improve the safety profile of buprenorphine.

Morphine Inhibited the Rat Neural Stem Cell Proliferation Rate by Increasing Neuro Steroid Genesis.

Up to present, a large number of reports unveiled exacerbating effects of both long- and short-term administration of morphine, as a potent analgesic agent, on opium-addicted individuals and a plethora of cell kinetics, although contradictory effect of morphine on different cells have been introduced until yet. To address the potent modulatory effect of morphine on neural multipotent precursors with emphasis on endogenous sex-related neurosteroids biosynthesis, we primed the rat neural stem cells isolated from embryonic rat telencephalon to various concentrations of morphine including 10, 20, 50 and 100µM alone or in combination with naloxone (100µM) over period of 72h. Flow cytometric Ki-67 expression and Annexin-V/PI based necrosis and apoptosis of exposed cells were evaluated. The total content of dihydrotestosterone and estradiol in cell supernatant was measured by ELISA. According on obtained data, both concentration- and time-dependent decrement of cell viability were orchestrated thorough down-regulation of ki-67 and simultaneous up-regulation of Annexin-V. On the other hand, the addition of naloxone (100µM), as Mu opiate receptor antagonist, could blunt the morphine-induced adverse effects. It also well established that time-course exposure of rat neural stem cells with morphine potently could accelerate the endogenous dihydrotestosterone and estradiol biosynthesis. Interestingly, naloxone could consequently attenuate the enhanced neurosteroidogenesis time-dependently. It seems that our results discover a biochemical linkage between an accelerated synthesis of sex-related steroids and rat neural stem cells viability.

Simultaneous analysis of codeine and its active metabolites in human plasma using liquid chromatography–tandem mass spectrometry: Application to a pharmacokinetic study after oral administration of codeine

A rapid and sensitive bioassay based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) has been developed and validated for the simultaneous determination of codeine and its active metabolites, including morphine, morphine 3β-glucuronide (M3G) and morphine 6β-glucuronide (M6G), in human plasma. Sample preparation of plasma after the addition of naloxone as internal standard (IS) involved solid-phase extraction (SPE) on C18 cartridges. Reversed-phase chromatography using a gradient elution with methanol and 0.04% formic acid solution (pH 3.5) was used for separation in a run time of 5min. The analytes were detected in the positive ion mode using multiple reaction monitoring (MRM) of the transitions at m/z 300.4→215.2 for codeine, 286.2→152.0 for morphine, and 462.2→286.2 for M3G and M6G. The method has the following performance characteristics: a reliable response range of 0.05–80ng/ml for codeine, M3G and M6G and a response range of 0.05–5.0ng/ml for morphine with correlation coefficients (r) of >0.997 for all analytes. The lower limit of quantitation (LLOQ) for all four analytes was 0.05ng/ml. The intra- and inter-day precision and accuracy of the quality control samples at low, medium and high concentration levels showed <12% relative standard deviation (RSD) and −6.9 to 8.1% relative error (RE) for all the analytes. The method was successfully applied to a pharmacokinetic study of codeine in healthy Mongolian Chinese volunteers after a 30mg oral dose.

Locomotor activity and contracture of isolated ileum precipitated by naloxone following treatment of guinea-pigs with a single dose of morphine

Guinea-pigs treated with a single dose of morphine, 15 mg kg-1 s.c., exhibited an increase in locomotor activity 2 h later on injection of naloxone, 4 mg kg-1 i.p. At the same time, contracture of ileal preparations isolated from morphine-treated guinea-pigs occurred on addition of naloxone 1 microM. Contracture of the ileum was inhibited by the tachykinin antagonist, spantide, and was therefore presumably mediated by a substance P-like agent. This study has established a useful model for the parallel investigation of central and enteric nervous system mechanisms of opiate dependence.

25-HYDROXYVITAMIN D, DEMENTIA, AND CEREBROVASCULAR PATHOLOGY IN ELDERS RECEIVING HOME SERVICES

Data concerning the effects of morphine on human pancreatic secretion are fragmentary and inconclusive. In the present study, we evaluated the effects of morphine on pure pancreatic secretion in nine subjects with external transduodenal drainage of the main pancreatic duct performed after biliary tract surgery. Intravenous infusion of a small dose of morphine, 40 microgram/kg/h, during pancreatic stimulation with secretin and cholecystokinin, caused a significant increase in volume, bicarbonate, and calcium secretion, and a significant decrease in protein secretion. The stimulatory effect on water and electrolyte secretion was rapid and much more pronounced, reaching about 45-50% of the control levels, whereas the inhibition of protein output was slightly delayed and of lesser magnitude, reaching about 20-25% of the control values. Both effects were long-lasting. The addition of naloxone, potent opiate antagonist, prevented in part the effects of morphine on pancreatic secretion, suggesting that specific opiate receptors might be involved in these effects.

The clinical efficacy and abuse potential of combination buprenorphine–naloxone in the treatment of opioid dependence

Background: Opioid dependence is a chronic relapsing condition for which long-term opioid substitution treatment (OST) is effective. However, safety and community acceptance of OST is compromised by diversion of prescribed medication. The development of a formulation combining buprenorphine and naloxone is designed to reduce the likelihood of intravenous misuse, and the therefore the value of the medication if diverted to the black market. Objective: To evaluate the evidence for 4:1 buprenorphine–naloxone as an efficacious OST, and as a deterrent to diversion and intravenous misuse. Methods: The literature on buprenorphine–naloxone in a 4:1 ratio is reviewed. Results/conclusion: The addition of naloxone does not appear to affect the efficacy of buprenorphine as a maintenance drug. While offering some deterrence of injection through precipitated withdrawal, there are many circumstances where injecting of buprenorphine–naloxone is reinforcing rather than aversive. The combination will reduce, but not eliminate, intravenous misuse; clinicians therefore need to monitor patients in OST, and be selective in providing patients with medication to be taken without observation.

Functional Interaction Between Purinergic System and Opioid Withdrawal: In Vitro Evidence

The effects exerted by P1 and P2 as well as by A1 and A2 agonists and antagonists purinoceptor on the acute opiate withdrawal induced by morphine were investigated in vitro. Following a 4 min in vitro exposure to morphine, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. The P1 purinoceptor agonist, adenosine, was able dose-dependently to reduce morphine withdrawal whereas alpha,beta-methylene ATP (APCPP), a P2 purinoceptor agonist, increased morphine withdrawal. Caffeine, a P1 purinoceptor antagonist, was able significantly and in a concentration dependent manner to increase morphine withdrawal whereas quinidine, a P2 receptor antagonist, reduced it. Also, the adenosine A1 receptor agonist, N6-Cyclopentyladenosine (CPA) was able to reduce dose-dependently naloxone-precipitated withdrawal whereas the selective adenosine A(2A) receptor agonist CGS 21680 increased the naloxone-precipitated withdrawal phenomenon. Dipyridamole, a blocker of adenosine reuptake, induced a significant reduction of morphine dependence. Caffeine, an adenosine receptor antagonist, significantly increased the naloxone-precipitated withdrawal effect in a concentration dependent manner. The same effect was observed with 8-phenyltheophylline (8PT), an A1 adenosine receptor antagonist, whereas 3,7-dimethyl-1-propargylxanthine (DMPX), an A2 adenosine receptor antagonist, reduced the naloxone-precipitated withdrawal phenomenon. The results of our experiments indicate that P1 and P2 as well as A1 and A2 purinoceptor agonists and antagonists are able to influence opiate withdrawal in vitro, suggesting an important functional interaction between the purinergic system and opioid withdrawal.

&amp;#945; 2-Adrenoceptor Antagonist SL84.0418 Involvement in the Development of Opioid Withdrawal

The effects exerted by a novel α2-adrenoceptor antagonist SL84.0418 on the acute opiate withdrawal induced by morphine (μ and κ opioid receptor agonist), DAMGO (highly selective μ opioid receptor agonist) and U-50488H (highly selective k opioid receptor agonist) was investigated in vitro. Furthermore, a comparative study was performed with yohimbine, a well known α2-adrenoceptor antagonist. Following a 4 min in vitro exposure to the opioid agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone (80% of contraction vs acetylcholine control) whereas per se the addition of SL84.0418 and yohimbine before naloxone did not induce contracture. The addition of SL84.0418 (1x10-6-5x10-6-1x10-5 M) 10 min before each opioid agonist produced a concentrationdependent increase of the opioid withdrawal and its efficacy was comparable to yohimbine (1x10-6-5x10-6-1x10-5 M). The results of our experiments indicate that SL84.0418 is able to influence opiate withdrawal in vitro thus confirming an important functional interaction between the noradrenergic system and opioid withdrawal.

&amp;#946;-Endorphin Fragments DT&amp;#947;E and DE&amp;#947;E Reduced Morphine Inhibition of Electrically-Induced Contractions and Opiate Withdrawal

The effect exerted by two gamma-endorphin derivatives (DTgammaE and DEgammaE) was investigated on morphine-induced inhibition on the electrically induced contractions of guinea pig ileum in vitro. Morphine (1x10(-8)-5x10 (-8)-1x10 (-7) M) dose dependently and significantly reduced the E.C. of guinea pig ileum, IC50=6.5x10(-8) M (Confidence limits: 3.7x10 (-8)-9.1x10 (-8)). DTgammaE and DEgammaE per se (1x10 (-6)-5x10 (-6)-1x10 (-5) M) did not modify significantly the E.C. of guinea pig ileum. Furthermore, DTgammaE or DEgammaE injection 10-30-60 min before morphine, did not affect the inhibitory effect of morphine on the E.C. of guinea pig ileum. By contrast, ilea from guinea-pigs treated for 4 days with DTgammaE or DEgammaE (1 mg/Kg/i.p.) were less sensitive to the inhibitory effect of morphine, IC50=8.3x10 (-7) M (Confidence limits: 1.4x10(-6)-3.5x10(-7)) for DTgammaE and IC50=7.7x10(-7) M (Confidence limits: 2.7x10(-6)-8.7x10(-7 )) for DEgammaE . The effect exerted by two beta-endorphin fragments (DTgammaE and DEgammaE) was investigated on the acute opiate withdrawal induced by micro, kappa and delta receptor agonists in vitro. After a exposure in vitro for 4 min to morphine (less selective micro agonist), DAGO (highly selective micro agonist), U50-488H (highly selective kappa agonist) and beta-endorphin (selective micro- delta agonist), a strong contracture of isolated guinea pig ileum was observed after the addition of naloxone. This effect was also observed when isolated rabbit jejunum was pretreated with deltorphin (highly selective delta agonist). DTgammaE or DEgammaE injection before or after treatment with morphine, DAGO, U50-488H, beta-endorphin or deltorphin was able of both preventing and reversing the naloxone-induced contracture after exposure to the opioid agonists in a concentration-dependent fashion. Our results indicate that both DTgammaE or DEgammaE are able to reduce significantly opiate withdrawal in vitro, suggesting an important functional interaction beween beta-endorphin fragments and opioid withdrawal at both micro, kappa and delta receptor level. Our results indicate that chronic treatment of guinea pigs with DTgammaE or DEgammaE induces a significant reduction of the inhibitory effect of morphine on the E.C. of guinea-pig ileum thus confirming an important functional interaction between gamma-endorphin derivatives and opioid system.

Comparison with Naloxone of Two Dynorphin a Analogues with K- and &amp;#948;-Opioid Antagonist Activity

Recently, we have demonstrated that substitution of 1,2,3,4 tetrahyidroisoquinoline-3- carboxylic acid (Tic) in place of Gly2 in dynorphin A-(1-13)-NH2 (DYN) analogue (A) decreased the affinity to the kappa, delta, and micro receptors, and kappa selectivity. The doubly substituted analogue [2',6'-dimethyl-L-tyrosine (Dmt1)-Tic2]DYN (B) exhibited high delta-affinity (Ki=0.39 nM) while micro- and kappa-affinities were only an order of magnitude less (4-5 nM). Bioactivity of [Tic2]DYN peptide (A) on guinea-pig ileum and rabbit jejunum revealed potent delta- and kappa-antagonism thus indicating that the conversion from a kappa-agonist to antagonist occurred with the inclusion of Tic into DYN analogues, similar to the appearance of antagonist properties with delta-opioid agonists containing a Tic2 residue. The present study was undertaken to compare the k- and delta-opioid antagonistic activity of two [Tic2] DYN peptides (A and B) with naloxone a well known non selective opioid receptor antagonist. This comparison was performed by using the model of opioid withdrawal in vitro. Following a 4 min in vitro exposure to U50-488 H (10(-8) M), a selective k opioid receptor agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone (10(-5) M). Also, following a 4 min in vitro exposure to deltorphin II (10(-8) M), a selective delta opioid receptor agonist, the rabbit jejunum exhibited a strong contracture after the addition of naloxone (10(-5) M). Results are expressed as percent of Ach contractions. In our study, we showed that in guinea pig ileum the peptide A (k opioid receptor antagonist) was able to induce a strong contracture at a concentration of 10(-9) M when injected 4 min after U50-488H (10(-8) M). Also, in rabbit jejunum the peptide B (delta-opioid receptor antagonist) was able to induce a strong contracture at a concentration of 10(-10) M when injected 4 min after deltorphin II (10(-8) M). The results of our experiments indicate that both peptide A (k receptor opiod antagonist) and peptide B (alpha receptor opioid antagonist) showed an antagonistic activity higher than naloxone.

Involvement of Serotonin in the Acute Dependence Produced by &amp;#956;, and K Opioid Agonists

Dependence can be induced and measured in vitro by using guinea-pig ileum. Tissues from untreated animals, after a brief exposure to opioids, show a strong naloxone-induced contracture indicating that the cellular mechanisms of dependence may occur very rapidly following occupation of receptors and that these mechanisms operate within the myenteric plexus. The characteristics of dependence development and the precipitation of withdrawal by naloxone in the guinea-pig ileum are very similar to those of acute dependence in experimental animals and man. Several observations indicate that brain serotoninergic system has been widely implicated in many of the pharmacological effects of opioids. Although the role of serotonin in the development of dependence has been previously reported the effects exerted by chronic treatment of p-Chlorophenylalanine (p-CPA), an inhibitor of tryptophan 5-hydroxylation which is the rate limiting step in the synthesis of serotonin, on the acute opiate withdrawal was investigated in vitro and whether p-CPA interferences on opiate withdrawal take place through μ and/or κ opioid receptors. Following a 4 min in vitro exposure to the opioid agonist (Morphine, DAGO or U50-488H), the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone (80% of contraction vs. acetylcholine control). By contrast, ilea from guinea-pigs treated for 6 days with p-CPA (10 mg/Kg/i.p.), following a 4 min in vitro exposure to the opioid agonist, did not show any contracture after the addition of naloxone (0% of contraction vs. acetylcholine control). The results of the present study confirm an important functional interaction between the serotoninergic system and opioid system.

Methisergide Selective Inhibition of Opioid Acute Physical Dependence in Isolated Tissues

Dependence can be induced and measured in vitro by using guinea-pig ileum. Tissues from untreated animals, after a brief exposure to opioids, show a strong naloxone-induced contracture indicating that the cellular mechanisms of dependence may occur very rapidly following occupation of receptors and that these mechanisms operate within the myenteric plexus. The characteristics of dependence development and the precipitation of withdrawal by naloxone in the guinea-pig ileum are very similar to those of acute dependence in experimental animals and man. Several observations support the hypothesis that brain serotoninergic system has been widely implicated in many of the pharmacological effects of opioids. Manipulations that alter the activity of serotonin in the central nervous system (CNS) modify the effects of morphine. Furthermore, chronic administration of morphine to mice has been reported to increase turnover of 5-HT turnover in the brain thus confirming a strong link between serotoninergic and opioid system. Therefore, the effects exerted by methisergide, a blocker of serotonin receptor, on the acute opiate withdrawal was investigated in vitro. Following a 4 min in vitro exposure to the opioid agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone (80% of contraction vs acetylcholine control). Methisergide (10(-7)-5 x 10(-7)-10(-6) M) treatment before or after the opioid agonists was able to respectively prevent or reverse the naloxone-induced contraction in isolated guinea pig ileum exposed to micro (morphine and DAMGO) opiate agonists in a concentration-dependent fascion whereas the k (U50-488H) opiate agonist significantly increased opiate withdrawal. The results of the present study confirm an important functional interaction between the serotoninergic and opioid system.

Induction of ovarian growth in the red claw crayfish, Cherax quadricarinatus, by the enkephalinergic antagonist naloxone: in vivo and in vitro studies

Summary The effects of spiperone and domperidone (dopaminergic antagonists), as well as naloxone (enkephalinergic antagonist) on ovarian growth of the crayfish Cherax quadricarinatus, were evaluated during the non-reproductive period. In vivo assays were carried out by administering these compounds by adding them to the crayfish food, and subsequently measuring the oocyte diameter (oocytes in secondary vitellogenesis). Only naloxone produced a significantly (p <0.05) higher oocyte diameter than that of the controls, suggesting that this antagonist was blocking the effects of endogenous enkcephalins on the secretion of one or more neurohormones involved in crustacean reproduction. To test this hypothesis, an in vitro incubation of ovarian pieces with thoracic ganglion (TG), a source of the gonad stimulating hormone (GSH), or eyestalk tissue (ET), the source of the gonad inhibiting hormone (GIH), with or without naloxone added to the incubation medium, was done. A significant increase of ovarian growth was observed when TG was present. Moreover, the addition of naloxone to this preparation was able to further increase the ovarian growth, presumably by preventing enkephalinergic inhibition of GSH secretion.

The Role of Muscarinic Receptors in the Control of Acute Opioid Withdrawal

Dependence can be induced and measured in vitro by using guinea-pig ileum. After a brief exposure to opioids, tissues from untreated animals, show a strong naloxone-induced contracture indicating that the cellular mechanisms of dependence may occur very rapidly following occupation of receptors and that these mechanisms operate within the myenteric plexus. Several observations indicate that acethilcoline (Ach) is involved in pharmacological effects of morphine and it is one of neurotransmitters widely involved in the expression of opioid withdrawal. This is confirmed by data showing that atropine, a well known muscarinic receptor, is able to block the symptoms of opiate withdrawal. Five subtypes muscarinic receptors, M1-M5, have been identified by pharmacological studies. The availability of agonists and antagonists for M1-M5, provides powerful tools that can be used to determine the roles of these receptor types in mediating some of physiological and pharmacological effects of muscarinic receptors in the central nervous system (CNS). The experiments described here were undertaken to provide insight into the role of M1-M5 muscarinic receptors subtypes in mediating opioid withdrawal. Therefore, the effects exerted by M1-M5 muscarinic receptors antagonists on the acute opiate withdrawal induced by opioids were investigated in vitro. Following a 4 min in vitro exposure to morphine or DAGO or U50-488H the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. The addition of pirenzepine, the M1 muscarinic receptor antagonist (1x10-8-5x10-8-1x10-7 M) 10 min before each opioid agonist produced a concentration-dependent reduction of the opioid withdrawal. Very similar results were obtained with metoctramine (M2 muscarinic receptor antagonist) with 4-DAMP (M3 muscarinic receptor antagonist) with himbacine (M4 muscarinic receptor antagonist) and PD 102807 (M5 muscarinic receptor antagonist). The results of our experiments indicate that M1-M5 muscarinic receptors antagonists are able to reduce opioid withdrawal in vitro thus confirming an important functional interaction between the muscarinic system and opioid withdrawal. Keywords: M1-M5 muscarinic receptors, Opioid, Withdrawal, Guinea-pig ileum

Effect of chronic treatment of ohmefentanyl stereoisomers on cyclic AMP formation in Sf9 insect cells expressing human μ-opioid receptors

The binding affinity of ohmefentanyl stereoisomers for μ-opioid receptors and the effect of chronic ohmefentanyl stereoisomers pretreatments on intracellular cAMP formation were investigated in Sf9 insect cells expressing human μ-opioid receptors (Sf9-μ cells). Competitive assay of [ 3H]ohmefentanyl binding revealed that these isomers had high affinity for μ-opioid receptors in Sf9-μ cells. Isomer F9204 had the highest affinity for μ-opioid receptors with the K i value of 1.66 ± 0.28 nM. After pretreated Sf9-μ cells with increasing concentrations of these isomers for 6 h, addition of naloxone (1 μM) precipitated an overshoot of foskolin-stimulated cAMP accumulation. The ability of these isomers to induce cAMP overshoot differed greatly with the order of F9202 > F9205 > F9208 > F9206 > F9204 > F9207. Of these isomers, F9202 was 2.7-fold less potent than F9204 in receptor binding affinity, but 71.5-fold more potent in ability to induce cAMP overshoot. These results suggested that there was a significant stereo-structural difference among ohmefentanyl stereoisomers in ability to induce naloxone-precipitated cAMP overshoot in Sf9-μ cells.

Opioid dependence in myenteric neurons innervating the circular muscle of guinea-pig ileum.

Guinea-pigs were treated with morphine for 6-8 days by subcutaneous implantation of pellets, each containing a mixture of morphine base (120 mg) and morphine hydrochloride (35 mg). Each guinea-pig received a single pellet. Mechanical activity of the circular muscle was recorded in vitro in preparations comprising the circular muscle and myenteric plexus. Exposure to morphine was maintained by addition of 1 microM morphine to the organ baths. After 90 min, morphine was withdrawn, either by repeatedly washing tissues in morphine-free Krebs' solution, or by addition of naloxone to reduce the occupancy of the opioid receptors by morphine. Withdrawal of morphine resulted in markedly enhanced contractile activity compared with that in circular muscle-myenteric plexus preparations from untreated control guinea-pigs. The withdrawal contractions were abolished by tetrodotoxin (600 nM) and greatly reduced by hyoscine (1 microM), indicating that they resulted from action potential discharge in myenteric neurons that release acetylcholine onto the circular muscle. Activation of the cholinergic excitatory motor neurons was not secondary to synaptic activation by cholinergic interneurons, because hexamethonium (100 microM) did not affect withdrawal contractions. The withdrawal response may therefore arise in the cholinergic excitatory motor neurons themselves, or in neurons that activate them via noncholinergic mechanisms.

Dose ratio is important in maximizing naloxone enhancement of nalbuphine analgesia in humans

The analgesic effect of kappa partial agonist opioids (i.e. nalbuphine, pentazocine and butorphanol) is significantly greater in women. Recent evidence suggests that this sexual dimorphism may result from a naloxone-sensitive anti-analgesic effect that is activated along with, and summates with, the analgesic effect of these agents, resulting in decreased analgesia or increased pain. For example, nalbuphine (5 mg) produces profound anti-analgesia (i.e. enhanced pain) in men, but addition of a low dose of the opioid receptor antagonist naloxone (0.4 mg, opioid antagonist) induces significant analgesia in men and enhances nalbuphine analgesia in women. To further delineate the dose-dependent relationship of nalbuphine and naloxone, we recently evaluated the effect of a lower dose of nalbuphine (2.5 mg) with and without naloxone (0.4 mg) on dental postoperative pain. In women, nalbuphine alone induced modest short duration analgesia, which was antagonized by the addition of naloxone. In men, this dose of nalbuphine alone did not produce analgesia or anti-analgesia, and naloxone did not alter the response to nalbuphine. Thus, it appeared that the 2.5 mg dose of nalbuphine was not sufficient to induce anti-analgesia while the 0.4 mg dose of naloxone was able to antagonize the analgesic effect of nalbuphine, at least in women. In the current study, we tested the hypothesis that an important determinant of naloxone enhancement of nalbuphine analgesia is the dose ratio of nalbuphine to naloxone. Since a dose ratio of 12.5:1 (i.e. 5 mg nalbuphine:0.4 mg naloxone) resulted in analgesic enhancement, but a dose ratio of 6.25:1 (2.5 mg:0.4 mg) did not, we tested the same, lower, dose of nalbuphine (2.5 mg) in combination with a lower dose of naloxone (0.2 mg) to maintain the 12.5:1 dose ratio. This lower dose of naloxone significantly prolonged the analgesic effect of nalbuphine in both men and women, suggesting that the anti-analgesic effect of nalbuphine is present in both sexes at the 2.5 mg dose and that the dose ratio of nalbuphine to naloxone is an important determinant of the analgesic efficacy of this combination.

The effect of papaverine on acute opiate withdrawal in guinea pig ileum.

In the present work the effect of papaverine, a non specific smooth muscle relaxant, was investigated on the naloxone-precipitated withdrawal contracture of the acute morphine-dependent guinea-pig ileum in vitro. Furthermore, the effect of papaverine was also considered on DAGO (highly selective mu -agonist) and U50-488H (highly selective k-agonist) withdrawal to test whether the possible interaction of papaverine on opioid withdrawal involves mu - and/or k-opioid receptors. Following a 4 min in vitro exposure to opioid agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. Papaverine treatment (1 x 10(-7) - 5 x 10(-7) - 1 x 10(-6) M) before or after the opioid agonists was able of both preventing and reversing the naloxone-induced contracture after exposure to mu (morphine and DAGO) or k (U50-488H) opiate agonists in a concentration-dependent fascion. Both acetylcholine response and electrical stimulation were not affected by papaverine treatment whereas the final opiate withdrawal was still reduced. The results of the present study indicate that papaverine was able to produce significative influence on the opiate withdrawal in vitro and papaverine was able to exert its effect both at mu and k opioid agonists.