A spirohydantoin derivative of oxymorphone: an agonist with delayed antagonist activity

We have synthesized a novel derivative of oxymorphone, oxymorphone-6 alpha-spirohydantoin. The derivative was less toxic in mice than the parent compound and it showed a significant anticonvulsive activity. It exerted agonist effects in doses lower than those of morphine and its agonist effects were longer lasting. Furthermore, both oxymorphone and the 6-spirohydantoin showed definite antagonist properties 48 hr later: they prevented analgesic effects of morphine. The antagonist effects of the derivative persisted for a week.

A comparison of morphine, meperidine, and oxymorphone as utilized in patient-controlled analgesia following cesarean delivery

Seventy-five patients (n = 75) undergoing elective cesarean delivery during epidural anesthesia were randomly assigned to receive one of three opioid analgesics via patient-controlled analgesia (PCA) when they first complained of pain in the recovery room. Following administration of an analgesic loading dose, patients were allowed to self-administer morphine 1.8 mg, meperidine 18 mg, or oxymorphone 0.3 mg iv every 8 min as required. Data collected during the 24-h observation period included visual analog scale (VAS) pain scores at rest and during movement, VAS patient satisfaction scores, total drug administered, the ratio of attempts/injections, and the incidence of nausea/vomiting, sedation, and pruritus. After adjusting for narcotic potency, no differences in 24-h dose requirements were noted between treatment groups (NS). All patients achieved an excellent level of analgesia at rest (NS); however, onset was most rapid with oxymorphone (P less than 0.05). The percentage of patients reporting severe pain during movement was highest in the meperidine group (P less than 0.05). Oxymorphone was associated with the highest incidence of nausea and vomiting (P less than 0.05), whereas increased sedation and pruritus were noted with morphine. Patient satisfaction with drug effect demonstrated significant negative correlations with resting pain scores and degree of sedation. Whereas morphine is a more commonly utilized PCA analgesic, the excellent analgesia, low incidence of sedation, and high patient satisfaction provided by meperidine and oxymorphone suggested useful alternatives.

Evaluation of pentamorphone in humans: a new potent opiate

We evaluated the analgesic properties of 14-beta-n-pentylaminomorphinone (pentamorphone), a new morphinan derivative, in 23 male volunteers divided into 6 groups who were given either placebo (1 per group) or 0.015, 0.03, 0.06, 0.12, 0.24, 0.48 microgram.kg-1 pentamorphone intravenously. Analgesia was evaluated by the maximal tolerance to a spring-loaded rod on the tibia and manubrium. Analgesic assessments and arterial blood samples were taken prior to and at set time intervals following drug administration. Pentamorphone produced a linear increase in pain tolerance with increasing dose as well as a dose-dependent depression of ventilation. Pentamorphone had no effect on blood pressure or heart rate in the doses used. Plasma histamine levels at 5 minutes were not elevated with any of the dosages. Pentamorphone appears to be an analgesic with clinically tolerable side effects in the range 0.12 to 0.24 microgram.kg-1 that merits further evaluation under clinical conditions.

Effects of oxymorphazone in frogs: long lasting antinociception in vivo, and apparently irreversible binding in vitro

Oxymorphazone (at doses of 50-200 mg/kg) was found to be a relatively weak antinociceptive drug in intact frog (Rana esculenta) when acetic acid was used as pain stimulus. Frogs remained analgesic for at least 48 hrs following oxymorphazone (200 mg/kg) administration. The ligand increased the latency of wiping reflex in spinal frogs too. These effects were blocked by naloxone. In equilibrium binding studies (3H)oxymorphazone had high affinity to the opioid receptors of frog brain and spinal cord as well (apparent Kd values were 8.9 and 10.6 nM, respectively). Kinetic experiments show that only 25% of the bound (3H)oxymorphazone is readily dissociable. Preincubation of the membranes with labeled oxymorphazone results in a washing resistant inhibition of the opioid binding sites. At least 70% of the (3H)oxymorphazone specific binding is apparently irreversible after reaction at 5 nM ligand concentration, and this can be enhanced by a higher concentration of tritiated ligand.

(8S)-(glutathion-S-yl)dihydromorphinone, a novel metabolite of morphine from guinea pig bile

A novel glutathione-conjugated metabolite of morphine has been isolated from the bile of guinea pigs given morphine. The metabolite was separated by preparative HPLC on a reverse phase column (YMC-GEL C18) using methanol/water (1:4, v/v) as eluate and purified by HPLC on another reverse phase column (mu-Bondapak phenyl) using water/acetonitrile/trimethylamine/acetic acid (150:3:2:1, v/v) as a mobile phase. The unambiguous structure assignment of the metabolite was performed by fast atom bombardment mass spectrometry and 400 MHz fourier transform NMR spectrometric analysis, and it was identified as (8S)-glutathion-S-yl)dihydromorphinone, in comparison with the synthetic morphinone-glutathione adduct.

A comparison of oxymorphone and fentanyl as narcotic supplements in general anesthesia

The safety and efficacy of two potent opiate analgesics, fentanyl and oxymorphone, used as adjuncts in general anesthesia, were studied in 39 patients undergoing elective gynecologic surgery of at least 2 hours duration. Based on a potency ratio of 10:1, patients received either fentanyl 6.5 micrograms/kg or oxymorphone 65 micrograms/kg prior to a thiopental 2 to 3 mg/kg succinylcholine induction and endotracheal intubation. Additional maintenance narcotic and isoflurane were administered as required by the "blinded" anesthesiologist in response to hemodynamic alterations 15% above a presurgical baseline. Overall analysis included hemodynamic response at preset intraoperative intervals, total anesthetic requirements, and stability of vital signs in the recovery room. Blood pressure and heart rate were reliably controlled with either agent; however, less narcotic (ml) and recovery room analgesics were required in the oxymorphone-treated group (p less than 0.05). Decreased naloxone requirements (p less than 0.05) and a more rapid emergence suggested that fentanyl was a safer agent when administered in relatively unrestricted fashion.

Aversive properties of opiate receptor blockade: evidence for exclusively central mediation in naive and morphine-dependent rats

The motivational effects of exclusively peripheral or central opiate receptor blockade were studied using place conditioning. Place aversions were observed with intraventricular (i.c.v.) methylnaloxone (MN) in both naive (200-1000 ng) and morphine-dependent rats (50-500 ng). Subcutaneous MN (0.03-10 mg/kg) was ineffective in naive rats; in dependent rats a small aversion was seen at the highest dose. Place aversions were not necessarily associated with behavioral signs of withdrawal. The data suggest that the aversive properties of opioid receptor antagonism are centrally mediated in both naive and dependent rats, and that their enhancement in morphine-dependent subjects results from a sensitized central mechanism rather than from the recruitment of a peripheral component.

Comparison of histamine release induced by morphine and oxymorphone administration in dogs

Cardiovascular effects (vasodilatation, hypotension) of morphine administration have been attributed to central actions and peripheral histamine release. In the study reported here, we compared plasma histamine (Hm) concentrations after morphine sulfate and oxymorphone HCl administration in conscious dogs. Five healthy adult dogs (mean body weight, 10.1 kg) were randomly administered morphine (2 mg/kg of body weight, IV) or oxymorphone (0.2 mg/kg, IV) by a 5-second bolus injection at weekly intervals. Venous blood samples (5 ml) were collected from jugular veins before and at 1, 2, 5, 15, 30, and 60 minutes after drug administration. Behavioral changes were recorded. Plasma was analyzed by a radioenzymatic technique, using purified histamine N-methyltransferase as an enzyme catalyst (sensitivity of assay, 40 pg Hm/ml). Mean base-line Hm value for all dogs was 0.55 ng/ml. The mean Hm value was significantly higher (P less than 0.05) than the base-line value at 1, 2, 5, 15, and 60 minutes after morphine administration (531.4, 251.0, 113.0, 31.5, and 1.0 ng of Hm/ml, respectively), but there were no significant increases in histamine values from base-line values at any time after oxymorphone administration. All dogs given morphine and 1 dog given oxymorphone showed excitatory behavior; 2 dogs given morphine and 3 dogs given oxymorphone salivated profusely.

Irreversible opiate agonists and antagonists. IV. Analgesic actions of 14-hydroxydihydromorphinone hydrazones

Several phenylhydrazone derivatives of oxymorphone [phenylhydrazone and p-nitrophenylhydrazone (OxyPNPH)] as well as oxymorphonazine produce a wash-resistant inhibition of radiolabeled opioid binding, suggesting nonequilibrium binding to opiate receptors. All are agonists and, in an effort to correlate their prolonged inhibition of binding with their pharmacology, we examined their analgesic actions in vivo. Dose-response curves at 1 hr revealed similar potencies of oxymorphone and the derivatives, with the exception of OxyPNPH which was significantly less potent. After 10 hr, oxymorphone at doses up to 50 mg/kg did not demonstrate any effect. In contrast, OxyPNPH at 25 mg/kg elevated tail-flick latencies from 2 to over 8 sec after 10 hr. The 50-mg/kg dose elevated latencies to approximately 5 sec after 24 hr. Oxymorphonazine and oxymorphone phenylhydrazone also produced a prolonged analgesia, although not as effectively as OxyPNPH. The prolonged analgesic actions of OxyPNPH were highly dependent upon a critical period of 2 to 3 h immediately after injection. Blockade of receptors during this period with naloxone prevented analgesia at all time points examined. If the long duration of action of OxyPNPH resulted simply from a long half-life and persistent-free compound within the brain, analgesia should have returned by 8 hr, at which time naloxone has been eliminated. The absence of analgesia 8 hr after both OxyPNPH and naloxone argues against simple pharmacokinetic mechanisms for the prolonged analgesia and is consistent with persistent receptor occupation. OxyPNPH (25 mg/kg) administered in vivo lowered radiolabeled opioid binding effectively in brain membranes despite extensive washing. OxyPNPH lowered mu1 binding by approximately 60% and mu2 binding by 35% whereas delta binding was not lowered significantly.

Oxymorphone: cardiovascular, pulmonary, and behavioral effects in dogs

Cardiovascular, pulmonary, and behavioral effects of multiple doses of oxymorphone in 10 nonanesthetized, spontaneously breathing, healthy dogs were studied. Oxymorphone (0.4 mg/kg of body weight) was administered IV, and at 20, 40, and 60 minutes after the first injection was given, 0.2 mg of oxymorphone/kg was administered. Cardiovascular and pulmonary variables were measured before (base line) and at 5, 15, 35, 55, 75, 100, 120, 150, 180, 210, 240, 270, and 300 minutes after the first oxymorphone injection. Degree of sedation and behavioral effects also were recorded. Naloxone (0.04 mg/kg, IV) was administered 4.5 hours after the 4th oxymorphone injection, and behavioral changes were recorded. Oxymorphone induced mild respiratory depression. After transient apnea developed, respiratory rate increased to a pant, tidal volume decreased, and minute ventilation increased, but these values were not significantly (P = 0.05) different from base line. The PaCO2, physiologic dead space, and base deficit increased; alveolar tidal volume decreased; and alveolar minute ventilation did not change. The PaO2 decreased, hemoglobin and arterial O2 content increased, and O2 transport did not change. Venous admixture transiently increased. Oxymorphone induced minimal cardiovascular depression. Mean arterial blood pressure, stroke volume, central venous pressure, pulmonary artery pressure, and pulmonary wedge pressure increased. Heart rate decreased, systemic vascular resistance transiently increased, and cardiac output transiently decreased. Because the dogs moved spontaneously, responded to sound with sudden, vigorous movements, and breathed with excessive effort, oxymorphone alone was considered inadequate as a general anesthetic.

Hybrid bivalent ligands with opiate and enkephalin pharmacophores

Bivalent ligands consisting of oxymorphamine and [D-Glu2]enkephalin pharmacophores linked through a spacer attached to the 6-amino group of the former and D-Glu of the latter were synthesized in an effort to investigate the possible coexistence of mu and delta recognition sites in the same opioid receptor complex. Of the two bivalent ligands (1,2) synthesized, only 1 had substantially greater antinociceptive potency in mice than its monovalent analogues (1a, 1b). Testing of 1, 1a, and 1b in the guinea pig ileum preparation (GPI) revealed a potency profile similar to that found in vivo, whereas no correlation was observed in the mouse vas deferens (MVD). Binding data indicated the same rank-order affinities at delta receptors as the opioid activities in the GPI and in mice. However, mu binding exhibited no relationship with activity. These results are consistent with the simultaneous occupation of mu and delta by a single bivalent ligand 1, but they are also in harmony with the interaction of 1 with an opioid receptor and an accessory binding site.

Differential effects of mu and kappa opioid analgesics on cerebral glucose utilization in the rat

The autoradiographic 2-deoxy-D-[1-(-14)C]glucose ([14C]2-DG) method was used to map the effects of subcutaneous (s.c.) morphine (8.0 mg/kg), oxymorphone (0.4 mg/kg) and nalbuphine (16.0 mg/kg) on local cerebral glucose utilization (LCGU), an index of local brain function. At the dosages administered, effects of the opioid agonists on LCGU were very restricted. The mu agonists, injected 15 min before [14C]2-DG, decreased LCGU in thalamic nuclei, including some of those which have been implicated in somatosensory processing, and in the dorsal tegmental nucleus. Nalbuphine did not produce these effects, but stimulated LCGU in nuclei of the spinal tract of the trigeminal nerve and in the globus pallidus. All of the effects on LCGU were blocked by prior administration of naloxone (1.0 or 10.0 mg/kg, s.c., 5 min before morphine or nalbuphine, respectively). Our findings suggest that different supraspinal mechanisms are involved in the actions of mu vs kappa opioids, and indicate that the [14C]2-DG procedure might be helpful in elucidating the anatomical areas involved.

Oxymorphone-naltrexonazine, a mixed opiate agonist-antagonist

Previous studies from our laboratories have reported the synthesis and pharmacological characteristics of a series of symmetrical opiate azines: naloxonazine, oxymorphonazine and naltrexonazine. We have now synthesized and characterized in binding assays and in vivo two asymmetrical azines: oxymorphone-naltrexonazine and oxymorphone-3-methoxynaltrexonazine. Oxymorphone-naltrexonazine, which theoretically could interact with the receptor as either an agonist or antagonist, displayed antagonist properties in vitro and in vivo. Oxymorphone-3-methoxynaltrexonazine, which theoretically could bind only as an agonist, possessed agonist properties in binding studies and was a potent analgesic in vivo.

Synthesis and binding of 3H-oxymorphazone to rat brain membranes

Oxymorphazone is a 14-hydroxydihydromorphinone derivative which contains a C-6 hydrazone group and hence could serve as an irreversible label for opioid receptors. 3H-oxymorphazone was synthesized by the reaction of 3H-oxymorphone with excess hydrazine. A specific radioactivity of 640 GBq/mmol (17,3 Ci/mmol) was achieved. Both the unlabelled compound and the tritiated ligand show high affinity to mu and kappa opiate receptor subtypes in rat brain membranes. Two binding sites were detected by equilibrium binding studies, with apparent Kd values of 0.62 nM and 28 nM. About 20% of the H-oxymorphazone specific binding is irreversible after reaction at 1 nM ligand concentration, and this can be enhanced by a higher concentration of tritiated ligand. No azine formation was detected. Preincubation of the membranes with unlabelled oxymorphazone resulted in an irreversible blockade of the high affinity 3H-naloxone binding sites.

Morphine metabolism in isolated rat hepatocytes and its implications for hepatotoxicity

Isolated rat hepatocytes metabolized morphine to its glucuronide conjugate, morphinone-glutathione conjugate, normorphine and morphinone. Addition of morphine to the isolated hepatocytes induced a marked decrease in the level of glutathione in the cells and resulted in cell death. The formation of glutathione conjugate was correlated well with the loss of intracellular glutathione. The cytotoxicity of morphinone was higher than that of morphine. Naloxone and normorphine showed no cytotoxic effect on the cells. Naloxone inhibited the formation of morphinone-glutathione conjugate and prevented the morphine-induced cytotoxicity. Naloxone also blocked morphine-induced liver damage in vivo. In contrast, the morphinone-induced hepatotoxicity was not prevented by naloxone. It is concluded that morphine has a hepatotoxic effect, that the morphine-induced hepatotoxicity is due to its metabolic activation, and that naloxone acts as an inhibitor of an enzyme converting morphine to morphinone.

Antagonism of stress-induced analgesia by quaternary naloxone

Both naloxone hydrochloride and the quaternary compound, naloxone methylbromide, significantly reduced antinociception elicited by 90 s of continuous footshock. Peripheral specificity of quaternary naloxone was demonstrated by its lack of antagonism of morphine analgesia. These results suggest that a significant portion of the antinociception elicited by these parameters of footshock and assessed by tail-flick procedures in rats is due to the activation of peripheral endorphins.

Purification and characterization of guinea pig liver morphine 6-dehydrogenase

Morphine 6-dehydrogenase, which catalyzes the dehydrogenation of morphine to morphinone, has been purified about 440-fold from the soluble fraction of guinea pig liver with a yield of 38%. The purified enzyme was a homogeneous protein on polyacrylamide gel disc electrophoresis and isoelectric focusing. The molecular weight and isoelectric point of the enzyme were 29,000 and 7.6, respectively. The enzyme utilizes both NAD and NADP as a cofactor, and the Km values were 0.12 mM for NAD and 0.42 mM for NADP. The Vmax values for morphine were 588 milliunits/mg of protein (with NAD) and 1600 milliunits/mg of protein (with NADP). The Km values for morphine were 0.12 mM (with NAD) and 0.49 mM (with NADP). The enzyme also exhibited activity for morphine-related compounds: nalorphine, normorphine, codeine, and ethylmorphine; however, 7,8-saturated congeners such as dihydromorphine and dihydrocodeine were poor substrates. The enzyme was inactivated by removal of 2-mercaptoethanol from the enzyme solution. The inactivated enzyme was rapidly recovered by the addition of 2-mercaptoethanol. Phenylarsine oxide and CdCl2 (dithiol modifiers) inhibited competitively toward cofactor binding and noncompetitively toward morphine binding. These results suggest that the enzyme possesses the essential thiol groups, probably vicinal dithiol, at or near the cofactor-binding site. Using the partially purified enzyme, 8-(2-hydroxyethylthio)dihydromorphinone was isolated as the product and identified by UV, mass, and NMR spectra. It was confirmed that morphinone proposed as the dehydrogenation product was nonenzymatically and covalently bound to 2-mercaptoethanol. Accordingly, the isolated morphinone-2-mercaptoethanol conjugate must be formed by two steps: enzymatic production of morphinone from morphine and then nonenzymatic binding of 2-mercaptoethanol to morphinone.

A quantitative study of [3H]D-Ala2-D-Leu5-enkephalin binding to rat brain membranes. Evidence that oxymorphone is a noncompetitive inhibitor of the lower affinity delta-binding site

The mechanism by which mu ligands inhibit the binding of prototypic delta agonists to preparations of brain membranes is controversial. Most investigators assume competitive inhibition. In this study, we examine the interaction of the mu agonist oxymorphone and delta agonist DSTLE (D-Ser2-Thr6-Leu-enkephalin) with [3H]D-Ala2-D-Leu5-enkephalin (DADL) binding to membranes of rat brain. According to the two-site competitive model, mu ligands are competitive inhibitors at both sites. The two-site allosteric model supposes that mu ligands are competitive inhibitors at one binding site, and noncompetitive inhibitors at the other binding site. Quantitative analysis of DSTLE and oxymorphone binding demonstrated that the two-site allosteric model fit the data significantly better than did the two-site competitive model, and that oxymorphone is a noncompetitive inhibitor of the lower affinity [3H]DADL-binding site. Autoradiographic studies demonstrated that the lower affinity [3H]DADL-binding site (mu-noncompetitive binding site) had an anatomical distribution apparently indistinguishable from that obtained with [3H]oxymorphone (type I pattern), supporting the hypothesis that the lower affinity delta-binding site is the delta-binding site of an opiate receptor complex consisting of interacting mu- and delta-binding sites.

Chloroacryloyl amides and alpha-methylenelactones from naltrexone, oxymorphone and fentanyl

A series of chloroacryloyl amides and alpha-methylenelactones were prepared from naltrexone and oxymorphone and some chloroacryloyl amides from fentanyl were prepared as potential Michael acceptors and irreversible ligands. The relative rates of Michael additions of p-methoxybenzenethiol to the double bonds were measured in an NMR spectrometer. The IC50's in rat brain homogenates and the irreversible binding to rat brain membranes were determined. In the methylene-lactone series, it was found that both the alpha and beta isomers derived from naltrexone and oxymorphone were excellent Michael acceptors, but only the beta isomers were more active in the opioid binding assays. The beta isomer derived from naltrexone was an irreversible ligand whereas the oxymorphone analogue was active only in the presence of 100 mM NaCl. In the chloroacryloyl series, only the alpha-chloroacryloyl amide derived from beta naltrexamine proved to be an irreversible binding ligand in the absence of NaCl. It was an excellent Michael acceptor. Under the conditions of our experiments, beta-FNA was a poor Michael acceptor and did not behave as an irreversible ligand in rat membranes.

Comparison of histamine release in human skin mast cells induced by morphine, fentanyl, and oxymorphone

Human leukocyte and skin mast cell preparations were incubated with morphine sulfate in concentrations ranging from 1.5 X 10(-5) M to 4.5 X 10(-3) M. Skin mast cells also were incubated with oxymorphone and fentanyl in the same concentrations. Human leukocytes did not release histamine in response to any concentration of morphine. In skin mast cells, histamine release by morphine first was detected at 1.5 X 10(-4) M. Histamine release further increased at 5.0 X 10(-4) M with no incremental increase at higher concentrations. Oxymorphone and fentanyl failed to release histamine at any concentration. Histamine release by morphine required calcium but was not influenced by changes in the 1-4 mM range. Skin mast cell preparations were pretreated for 30 min in naloxone 5 X 10(-4) M and then morphine 5 X 10(-4) M was added for 30 min without removing naloxone. Naloxone neither released histamine nor inhibited morphine-induced histamine release. The release of histamine by morphine but not equimolar concentrations of fentanyl and oxymorphone indicates that histamine release by narcotics is not a nonspecific effect of high drug concentration. The failure of naloxone to inhibit morphine-induced histamine release suggests that histamine release by morphine is not dependent on opiate receptor binding or activation. These results indicate that this human mast cell preparation will be useful in further understanding the mechanism of histamine release induced by morphine and other agents.

Diastereomeric 6-desoxy-6-spiro-alpha-methylene-gamma-butyrolactone derivatives of naltrexone and oxymorphone. Selective irreversible inhibition of naltrexone binding in an opioid receptor preparation by a conformationally restricted michael acceptor ligand

The diastereomeric 6-desoxy-6-spiro-alpha-methylene-gamma-butyrolactone derivatives of naltrexone (4a and 5a) and of oxymorphone (4b and 5b) were prepared from their parent ketones. Diastereomers 4a and 4b were obtained from the 3,14-diacetate derivatives of naltrexone (6a) and oxymorphone (6b) by reaction with the Reformatsky reagent prepared from methyl alpha-(bromomethyl)acrylate. Deacetylation with methanol completed the synthesis. Diastereomers 5a and 5b were obtained from oxiranes 8a and 8b, respectively. The oxiranes were allowed to react with the sodium salt of ethyl acetoacetate, followed by methenation and deprotection to complete the synthesis of 5a and 5b, respectively. Compound 5a was the most potent agent tested in competition against [3H]naltrexone in the opioid radioreceptor assay. At a concentration of 5 nM this compound produced a 50% inhibition of binding. The majority of this inhibition (30%) was irreversible, i.e., it remained even after extensive washing of the membrane preparation in the presence and absence of Na+. Naloxone protected against this irreversible effect. The data suggest a receptor nucleophile, perhaps a sulfhydryl group, is located where it can add to the alpha, beta-unsaturated carbonyl system of 5a.