Inhibition by levorphanol and related drugs of amino acid transport by isolated membrane vesicles from Escherichia coli.
Levorphanol inhibits the transport of the amino acids proline and lysine by cytoplasmic membrane vesicles derived from Escherichia coli. The degree of inhibition increases with increasing levorphanol concentration and ranges from 26% at 10(-6) M levorphanol to 92% at 10(-3) M levorphanol. The effect is independent of the energy source, since levorphanol inhibits proline uptake to the same extent in the presence of 20 mM d-lactate or 20 mM succinate and in the absence of an exogenous energy source. Levorphanol does not irreversibly alter the ability of membrane vesicles to transport proline, since incubation of membrane vesicles for 15 min in the presence of 0.25 mM levorphanol, a concentration which inhibits proline transport by more than 75%, has no effect on the rate of proline transport by these vesicles once the drug is removed. Both the maximum velocity and the K(m) of proline transport are modified by levorphanol, hence, the type of inhibition produced by levorphanol is mixed. The inhibitor constant (K(i)) for levorphanol inhibition of proline transport is approximately 3 x 10(-4) M. Membrane vesicles incubated in the presence of levorphanol accumulate much less proline at the steady state than do control vesicles. Furthermore, the addition of levorphanol to membrane vesicles preloaded to the steady state with proline produces a marked net efflux of proline. Levorphanol does not block either temperature-induced efflux or exchange of external proline with [(14)C]proline present in the intravesicular pool. Dextrorphan, the enantiomorph of levorphanol, and levallorphan, the N-allyl analogue of levorphanol, inhibit proline and lysine transport in a similar manner. Possible mechanisms of the effects of these drugs on cell membranes are discussed. (+info
Analgesic synergy between topical lidocaine and topical opioids.
Topical drugs avoid many of the problematic side effects of systemic agents. Immersion of the tail of a mouse into a solution of dimethyl sulfoxide (DMSO)-containing morphine produces a dose-dependent, naloxone-sensitive, analgesia (ED(50) 6.1 mM; CL 4.3, 8.4) limited to the portion of the tail exposed to the drug. DMSO alone in this paradigm had no analgesic activity. Like morphine, the opioids levorphanol (ED(50) 5.0 mM; CL 3.8, 7.8) and buprenorphine (ED(50) 1. 1 mM; CL 0.7, 1.5) were effective topical analgesics. Lidocaine also was active in the tail-flick assay (ED(50) 2.5 mM; CL 2.0, 3.4), with a potency greater than morphine. As expected, the free base of lidocaine was more potent than its salt. Combinations of a low dose of lidocaine with a low dose of an opioid yielded significantly greater than additive effects for all opioids tested. Isobolographic analysis confirmed the presence of synergy between lidocaine and morphine, levorphanol and buprenorphine. These studies demonstrate a potent interaction peripherally between opioids and a local anesthetic and offer potential advantages in the clinical management of pain. (+info
Differential regulation of the human kappa opioid receptor by agonists: etorphine and levorphanol reduced dynorphin A- and U50,488H-induced internalization and phosphorylation.
We previously observed that (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide (U50,488H) promoted internalization and phosphorylation of the FLAG-tagged human kappa opioid receptor (FLAG-hkor) stably expressed in Chinese hamster ovary (CHO) cells. In this study, we compared regulation of the FLAG-hkor expressed in CHO cells by U50,488H, dynorphin A, etorphine, and levorphanol, which were potent full agonists as determined by stimulation of guanosine 5'-O-(3-[(35)S]thio)triphosphate binding. Using fluorescence flow cytometry, we found that dynorphin A(1-17), like U50,488H, promoted internalization of the FLAG-hkor in a time- and dose-dependent manner. The antagonists naloxone and norbinaltorphimine, having no effect on FLAG-hkor internalization, effectively blocked dynorphin A(1-17)- and U50,488H-induced internalization. Interestingly, the full agonists etorphine and levorphanol did not cause internalization of the FLAG-hkor but significantly reduced dynorphin A(1-17)- and U50,488H-induced internalization in a dose-dependent manner. Immunofluorescence staining of FLAG-hkor yielded similar results. Dynorphin A(1-17) and U50,488H enhanced phosphorylation of FLAG-hkor to a greater extent than etorphine, but levorphanol did not increase FLAG-hkor phosphorylation. Etorphine or levorphanol decreased dynorphin- or U50,488H-induced phosphorylation. It is likely that conformations of the hkor required for phosphorylation and initiation of internalization are different from those for activation of G proteins. We also examined whether the four agonists had differential effects on superactivation of adenylate cyclase. Pretreatment with U50,488H, dynorphin A(1-17), or etorphine enhanced forskolin-stimulated adenylate cyclase activity to approximately 200 to 250% of the control, whereas levorphanol pretreatment did not result in significant adenylate cyclase superactivation. Thus, the degree of superactivation caused by an agonist is unrelated to its ability to promote internalization of the hkor. (+info
Oral opioid therapy for chronic peripheral and central neuropathic pain.
BACKGROUND: Although opioids are commonly used to treat chronic neuropathic pain, there are limited data to guide their use. Few controlled trials have been performed, and many types of neuropathic pain remain unstudied. METHODS: Adults with neuropathic pain that was refractory to treatment were randomly assigned to receive either high-strength (0.75-mg) or low-strength (0.15-mg) capsules of the potent mu-opioid agonist levorphanol for eight weeks under double-blind conditions. Intake was titrated by the patient to a maximum of 21 capsules of either strength per day. Outcome measures included the intensity of pain as recorded in a diary, the degree of pain relief, quality of life, psychological and cognitive function, the number of capsules taken daily, and blood levorphanol levels. RESULTS: Among the 81 patients exposed to the study drug, high-strength levorphanol capsules reduced pain by 36 percent, as compared with a 21 percent reduction in pain in the low-strength group (P=0.02). On average, patients in the high-strength group took 11.9 capsules per day (8.9 mg per day) and patients in the low-strength group took close to the 21 allowed (18.3 capsules per day; 2.7 mg per day). Affective distress and interference with functioning were reduced, and sleep was improved, but there were no differences between the high-strength group and the low-strength group in terms of these variables. Noncompletion of the study was primarily due to side effects of the opioid. Patients with central pain after stroke were the least likely to report benefit. CONCLUSIONS: The reduction in the intensity of neuropathic pain was significantly greater during treatment with higher doses of opioids than with lower doses. Higher doses produced more side effects without significant additional benefit in terms of other outcome measures. (+info
The competitive N-methyl-D-aspartate receptor antagonist (-)-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid (LY235959) potentiates the antinociceptive effects of opioids that vary in efficacy at the mu-opioid receptor.
(-)-6-Phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid (LY235959) is a competitive N-methyl-D-aspartate receptor antagonist shown to prevent the development of tolerance to the antinociceptive effects of morphine in rodents. Although administration of LY235959 alone generally does not produce antinociception, LY235959 potentiates the antinociceptive effects of morphine in squirrel monkeys. The present study was designed to determine whether LY235959 would potentiate the acute antinociceptive effects of morphine as well those of the opioid receptor agonists l-methadone, levorphanol, butorphanol, and buprenorphine. A squirrel monkey titration procedure was used in which shock (delivered to the tail) increased in intensity every 15 s (0.01-2.0 mA) in 30 increments. Five lever presses during any given 15-s shock period (fixed ratio 5) produced a 15-s shock-free period after which shock resumed at the next lower intensity. Morphine (0.3-3.0 mg/kg i.m.), l-methadone (0.1-0.56 mg/kg i.m.), levorphanol (0.1-1.0 mg/kg i.m.), butorphanol (1.0-10 mg/kg i.m.), and buprenorphine (0.01-0.03 mg/kg i.m.), but not LY235959 (0.1-1.0 mg/kg i.m.), dose and time dependently increased the intensity below which monkeys maintained shock 50% of the time (median shock level, MSL). LY235959 dose dependently potentiated the effect of each opioid agonist on MSL when concurrently administered to monkeys. Although LY235959 potentiated the antinociceptive effect of each opioid examined in a statistically significant manner, LY235959 seemed more potent and effective when combined with higher efficacy opioids. The present data suggest that the N-methyl-D-aspartate antagonist, LY235959, can potentiate the antinociceptive effects of a range of opioid receptor agonists independently of nonspecific motor effects. (+info
Anti-arrhythmic activities of opioid agonists and antagonists and their stereoisomers.
1. A series of opioid agonists, antagonists and their (+)-stereoisomers were tested for antiarrhythmic activity in the rat coronary artery occlusion model. 2. Naloxone (0.01-2 mg kg-1) significantly reduced the incidence and severity of cardiac arrhythmias, in accordance with previous published studies. 3. The non-opioid stereoisomer, (+)-naloxone, was equipotent with naloxone against occlusion-induced arrhythmia. 4. Similar non-stereospecific antiarrhythmic effects were induced by another opioid antagonist, Win 44,441-3 and its stereoisomer Win 44,441-2. 5. The opioid agonists, morphine and levorphanol, protected against occlusion-induced arrhythmia as did the opioid antagonists, and the (+)-stereoisomer, dextrorphan, was equipotent to levorphanol. 6. It is concluded that the antiarrhythmic effects of opioid drugs are not mediated by opioid receptors. A direct effect on ionic currents in cardiac muscle is suggested as the mechanism of opioid antiarrhythmic activity. (+info
QUANTITATIVE STUDIES OF THE ANTAGONISM BY NALORPHINE OF SOME OF THE ACTIONS OF MORPHINE-LIKE ANALGESIC DRUGS.
A quantitative investigation has been made of the antagonism by nalorphine of the analgesia and lenticular opacity produced in mice by a number of compounds. ED50 values have been obtained for each drug in the absence and in the presence of increasing doses of nalorphine, and from these, appropriate dose-ratios have been calculated. It has been possible to derive the equivalent of a pA(2) value for each drug with nalorphine and, since these are almost identical, it may be concluded that all the drugs combine with similar receptors. Nalorphine antagonizes both actions by competing for the receptors. It was not possible to antagonize quantitatively the analgesic action of pethidine with nalorphine, although the lenticular effect could be abolished. The effect of nalorphine on the change in skin temperature in mice induced by some of the analgesic drugs was also investigated. (+info
Differential effects of agonists on adenylyl cyclase superactivation mediated by the kappa opioid receptors: adenylyl cyclase superactivation is independent of agonist-induced phosphorylation, desensitization, internalization, and down-regulation.
Prolonged activation of opioid receptors followed by agonist removal leads to adenylyl cyclase (AC) superactivation. In this study, we examined in CHO cells stably expressing the human or rat kappa opioid receptor (hkor or rkor) whether agonists had differential abilities to induce AC superactivation and whether the hkor and rkor exhibited differential AC superactivation. Pretreatment of the hkor with (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide methanesulfonate (U50,488H) induced AC superactivation in a time- and dose-dependent manner, reaching a plateau at 4 h and 0.1 microM. The extents of AC superactivation after a 4-h pretreatment of the hkor with saturating concentrations of agonists were in the order of the full agonists U50,488H, dynorphin A(1-17), (+/-)-ethylketocyclazocine, etorphine, and U69,593 > the high-efficacy partial agonist nalorphine > the low-efficacy partial agonists nalbuphine, morphine, and pentazocine. Interestingly, the full agonist levorphanol caused much lower AC superactivation than other full agonists and reduced the AC superactivation induced by U50,488H and dynorphin A(1-17) in a dose-dependent manner. The order of relative efficacies of agonists in causing AC superactivation mediated by the rkor was similar to that mediated by the hkor and the extents of AC superactivation were slightly lower. Because the rkor does not undergo U50,488H (1 microM)-induced phosphorylation, desensitization, internalization, and down-regulation in these cells, the degree of AC superactivation is independent of these processes. This is among the first reports to demonstrate that relative efficacies of agonists in causing AC superactivation generally correlated with those in activating G proteins and a full agonist reduced AC superactivation induced by another full agonist. (+info