Nephrolithiasis among male patients with newly diagnosed gout.

INTRODUCTION: An elevated serum urate level is recognised as a cause of gouty arthritis and uric acid stone. The level of serum uric acid that accelerates kidney stone formation, however, has not yet been clarified. This study aimed to find out if a high serum urate level is associated with nephrolithiasis. METHODS: Patients were recruited from the rheumatology clinic of Taipei City Hospital (Renai and Zhongxing branches) in Taiwan from March 2015 to February 2016. A total of 120 Chinese male patients with newly diagnosed gout and serum urate concentration of >7 mg/dL and no history of kidney stones were divided into two groups according to their serum urate level: <10 mg/dL (group 1, n=80) and ≥10 mg/dL (group 2, n=40). The mean body mass index, blood urea nitrogen level, creatinine level, urinary pH, and kidney ultrasonography were compared between the two groups. RESULTS: There were no significant differences in blood urea nitrogen or creatinine level between the two groups. The urine pH in both groups was similar and not statistically significant. Kidney stone formation was detected via ultrasonography in 6.3% (5/80) and 82.5% (33/40) of patients in groups 1 and 2, respectively (P<0.05). CONCLUSION: A serum urate level of ≥10 mg/dL may precipitate nephrolithiasis. Further studies are warranted to substantiate the relationship between serum urate level and kidney stone formation.

Spinal antinociceptive effects of the novel NOP receptor agonist PWT2-nociceptin/orphanin FQ in mice and monkeys.

BACKGROUND AND PURPOSE: Using an innovative chemical approach, peptide welding technology (PWT), a tetrabranched derivative of nociceptin/orphanin FQ (N/OFQ) has been generated and pharmacologically characterized. Both in vitro and in vivo PWT2-N/OFQ displayed the same pharmacological profile to the natural ligand. It was more potent and produced longer-lasting effects. The aim of the present study was to investigate the spinal effects of PWT2-N/OFQ in nociceptive and neuropathic pain models in mice and non-human primates. EXPERIMENTAL APPROACH: Tail withdrawal assay in mice and monkeys was used as a nociceptive pain model and mechanical threshold in mice subjected to chronic constriction injury was used as a neuropathic pain model. The antinociceptive effects of spinally administered N/OFQ and PWT2-N/OFQ were assessed in these models. KEY RESULTS: PWT2-N/OFQ mimicked the spinal antinociceptive effects of N/OFQ both in nociceptive and neuropathic pain models in mice as well as in non-human primates displaying 40-fold higher potency and a markedly prolonged duration of action. The effects of N/OFQ and PWT2-N/OFQ were sensitive to the N/OFQ receptor (NOP) antagonist SB-612111, but not to opioid receptor antagonists. CONCLUSIONS AND IMPLICATIONS: The present study has demonstrated that PWT2-N/OFQ mimicked the antinociceptive effects of the natural peptide in rodents and non-human primates acting as a potent and longer-lasting NOP-selective agonist. More generally, PWT derivatives of biologically active peptides can be viewed as innovative pharmacological tools for investigating those conditions and states in which selective and prolonged receptor stimulation promotes beneficial effects.

Supraspinal actions of nociceptin/orphanin FQ, morphine and substance P in regulating pain and itch in non-human primates.

BACKGROUND AND PURPOSE: Nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor agonists display a promising analgesic profile in preclinical studies. However, supraspinal N/OFQ produced hyperalgesia in rodents and such effects have not been addressed in primates. Thus, the aim of this study was to investigate the effects of centrally administered ligands on regulating pain and itch in non-human primates. In particular, nociceptive thresholds affected by intracisternal N/OFQ were compared with those of morphine and substance P, known to provide analgesia and mediate hyperalgesia, respectively, in humans. EXPERIMENTAL APPROACH: Intrathecal catheters were installed to allow intracisternal and lumbar intrathecal administration in awake and unanaesthetized rhesus monkeys. Nociceptive responses were measured using the warm water tail-withdrawal assay. Itch scratching responses were scored from videotapes recording behavioural activities of monkeys in their home cages. Antagonist studies were conducted to validate the receptor mechanisms underlying intracisternally elicited behavioural responses. KEY RESULTS: Intracisternal morphine (100 nmol) elicited more head scratches than those after intrathecal morphine. Distinct dermatomal scratching locations between the two routes suggest a corresponding activation of supraspinal and spinal µ receptors. Unlike intracisternal substance P, which induced hyperalgesia, intracisternal N/OFQ (100 nmol) produced antinociceptive effects mediated by NOP receptors. Neither peptide increased scratching responses. CONCLUSIONS AND IMPLICATIONS: Taken together, these results demonstrated differential actions of ligands in the primate supraspinal region in regulating pain and itch. This study not only improves scientific understanding of the N/OFQ-NOP receptor system in pain processing but also supports the therapeutic potential of NOP-related ligands as analgesics.

Functional plasticity of the N/OFQ-NOP receptor system determines analgesic properties of NOP receptor agonists.

Despite high sequence similarity between NOP (nociceptin/orphanin FQ opioid peptide) and opioid receptors, marked differences in endogenous ligand selectivity, signal transduction, phosphorylation, desensitization, internalization and trafficking have been identified; underscoring the evolutionary difference between NOP and opioid receptors. Activation of NOP receptors affects nociceptive transmission in a site-specific manner, with antinociceptive effects prevailing after peripheral and spinal activation, and pronociceptive effects after supraspinal activation in rodents. The net effect of systemically administered NOP receptor agonists on nociception is proposed to depend on the relative contribution of peripheral, spinal and supraspinal activation, and this may depend on experimental conditions. Functional expression and regulation of NOP receptors at peripheral and central sites of the nociceptive pathway exhibits a high degree of plasticity under conditions of neuropathic and inflammatory pain. In rodents, systemically administered NOP receptor agonists exerted antihypersensitive effects in models of neuropathic and inflammatory pain. However, they were largely ineffective in acute pain while concomitantly evoking severe motor side effects. In contrast, systemic administration of NOP receptor agonists to non-human primates (NHPs) exerted potent and efficacious antinociception in the absence of motor and sedative side effects. The reason for this species difference with respect to antinociceptive efficacy and tolerability is not clear. Moreover, co-activation of NOP and µ-opioid peptide (MOP) receptors synergistically produced antinociception in NHPs. Hence, both selective NOP receptor as well as NOP/MOP receptor agonists may hold potential for clinical use as analgesics effective in conditions of acute and chronic pain.

Risk of adolescent offspring's completed suicide increases with prior history of their same-sex parents' death by suicide.

BACKGROUND: To investigate the risk of completed suicide in offspring during adolescence in relation to prior history of the same-sex parent's death by suicide and other causes. METHOD: A total of 500 adolescents who died by suicide at age 15-19 years between 1997 and 2007 were identified from the Taiwan Mortality Registration (TMR). For each case, 30 age- and time-matched controls were selected randomly from all adolescents registered in the Taiwan Birth Registry (TBR). A multivariate conditional logistic regression model was used to assess the risk of adolescent completed suicide in relation to their same-sex parent. RESULTS: Adolescent suicide risk was positively associated with both paternal [odds ratio (OR) 5.38, 95% confidence interval (CI) 2.17-13.33] and maternal suicide (OR 6.59, 95% CI 1.82-23.91). The corresponding risk estimates associated with paternal and maternal deaths from non-suicidal causes were much lower, at 1.88 and 1.94 respectively. The risk of suicide in male adolescents was significantly associated with prior history of paternal death by suicide (OR 8.23, 95% CI 2.96-22.90) but not of maternal death by suicide (OR 3.50, 95% CI 0.41-30.13). On the other contrary, the risk of suicidal death in female adolescents was significantly associated with prior history of maternal suicide (OR 9.71, 95% CI 1.89-49.94) but not of paternal suicide (OR 2.42, 95% CI 0.30-19.57). However, these differences did not reach statistical significance. CONCLUSIONS: Although limited by sample size, our study indicates that adolescent offspring suicidal death is associated with prior history of their same-sex parent's death by suicide.

[Dmt1]N/OFQ(1-13)-NH2: a potent nociceptin/orphanin FQ and opioid receptor universal agonist.

BACKGROUND AND PURPOSE: Intrathecally (i.t.) administered nociceptin/orphanin FQ (N/OFQ) evokes antinociceptive effects in rodents. Recent studies in monkeys demonstrated that i.t. co-application of N/OFQ and morphine elicits synergistic antinociceptive actions suggesting mixed N/OFQ peptide (NOP) and µ opioid receptor agonists as innovative spinal analgesics. Thus, novel N/OFQ related peptides were synthesized in order to identify and pharmacologically characterize a mixed NOP/ µ opioid receptor agonist. EXPERIMENTAL APPROACH: The following in vitro assays were used: calcium mobilization in cells expressing the human NOP or classical opioid receptors and chimeric G proteins, receptor and [(35)S]-GTPγS binding, [(35)S]-GTPγS binding in rat spinal cord membranes, guinea pig ileum bioassay. In vivo experiments were performed in monkeys using the tail withdrawal assay. KEY RESULTS: From calcium mobilization studies [Dmt(1)]N/OFQ(1-13)-NH(2) was selected as the most potent and least selective compound. The mixed NOP/opioid full agonist activity and high affinity of [Dmt(1)]N/OFQ(1-13)-NH(2) was confirmed at human recombinant receptors in receptor binding, calcium mobilization and/or [(35)S]-GTPγS binding studies, at rat spinal cord receptors in [(35)S]-GTPγS binding experiments, and at guinea pig receptors inhibiting neurogenic contractions in the ileum. In vivo in the tail withdrawal assay in monkeys i.t. [Dmt(1) ]N/OFQ(1-13)-NH(2) was able to elicit robust and long-lasting antinociceptive effects. CONCLUSIONS AND IMPLICATIONS: Collectively, these results demonstrate that [Dmt(1)]N/OFQ(1-13)-NH(2) behaves as NOP/opioid receptor universal agonist and substantiate the suggestion that such mixed ligands are worthy of development as innovative spinal analgesics.

Urbanization and prevalence of depression in diabetes.

OBJECTIVES: To depict recent secular trend (2001-2005) in prevalence of depression among diabetic population in Taiwan, and to explore the influences of urbanization on the prevalence of depression. STUDY DESIGN: A descriptive correlation study design relating urbanization and prevalence of depression. METHODS: Annual prevalence of depression was calculated as the ratio of number of individuals with depression (ICD-9-CM: 296, 309, or 311) to the size of diabetic population (ICD-9-CM: 250), which were ascertained from ambulatory care claim data of Taiwan's National Health Insurance between 2001 and 2005. Multivariate Poisson regression analysis was used to assess the secular trend in the prevalence of comorbid depression, and to appraise the influence of urbanization on prevalence of depression in diabetic patients. RESULTS: The prevalence of depression among diabetic population increased annually from 22.6/10(3) in 2001 to 27.0/10(3) in 2005 with a significantly and linearly rising trend (ß = 0.0461, p < 0.0001). Diabetic population living in urban areas showed the largest increase in prevalence (6.3/10(3)), followed by those from rural areas (5.6/10(3)). Compared to the diabetic patients residing in rural areas, those living in urban areas (RR = 1.28, 95% CI = 1.25-1.31) and those from satellite towns (RR = 1.22, 95% CI = 1.19-1.25) both had significantly increased adjusted RR. CONCLUSIONS: There is a significant increasing trend in prevalence of depression among diabetic population in recent years in Taiwan. Diabetic patients from urban areas not only had the greatest prevalence of depression but also showed the largest increase in prevalence during the study period, which highlights a need for managing depression in urban diabetes.

Incidence of renal and perinephric abscess in diabetic patients: a population-based national study.

This population-based cohort study aimed to investigate the incidence and relative hazard of renal and perinephric abscess (RA) in the diabetic population in Taiwan. More than a half million diabetic patients and sex- and age-matched controls were identified from the 1997 Taiwan National Health Insurance data and were linked to in-patient claims from 1997 to 2007. Person-year approach with Poisson assumption was used to estimate the incidence density (ID) of RA. The hazard ratios (HRs) of hospitalization due to RA in relation to diabetes were analysed using a Cox proportional hazard model. The ID for the diabetic and control subjects was 4·6 and 1·1/10,000 person-years, respectively, in 11 years of follow-up, representing an adjusted HR of 3·81 (95% confidence interval 3·44-4·23). This study confirmed the association of diabetes with RA, and argued that more aggressive urological care should be administered to diabetic patients.

Seizure activity involved in the up-regulation of BDNF mRNA expression by activation of central mu opioid receptors.

Chemical-induced seizures up-regulated brain-derived neurotrophic factor (BDNF) mRNA expression. Intracerebroventricular (i.c.v.) administration of endogenous opioids preferentially activating mu opioid receptor (MOR) could also increase BDNF mRNA expression. The aim of this study was to determine to what extent i.c.v. administration of synthetic MOR-selective agonists in rats can modulate both seizure activity and up-regulation of BDNF mRNA expression. Effects and potencies of i.c.v. administration of morphine and [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO), were directly investigated by scoring behavioral seizures and measuring BDNF mRNA expression. In addition, effects of the opioid receptor antagonist naloxone and antiepileptic drugs, diazepam, phenobarbital, and valproate, on i.c.v. MOR agonist-induced behavioral seizures and up-regulation of BDNF mRNA expression were determined. A single i.c.v. administration of morphine (10-100 microg) or DAMGO (0.15-1.5 microg) dose-dependently elicited behavioral seizures and increased BDNF mRNA expression in the widespread brain regions. However, s.c. administration of MOR agonists neither produced behavioral seizures nor increased BDNF mRNA expression. Pretreatment with naloxone 1 mg/kg significantly reduced behavioral seizure scores and the up-regulation of BDNF mRNA expression elicited by i.c.v. morphine or DAMGO. Similarly, diazepam 10 mg/kg and phenobarbital 40 mg/kg significantly blocked i.c.v. MOR agonist-induced actions. Pretreatment with valproate 300 mg/kg only attenuated behavioral seizures, but it did not affect morphine-induced increase of BDNF mRNA expression. This study provides supporting evidence that seizure activity plays an important role in the up-regulation of BDNF mRNA expression elicited by central MOR activation and that decreased inhibitory action of GABAergic system through the modulation on GABA receptor synaptic function by central MOR activation is involved in its regulation of BDNF mRNA expression.

Comparison of the opioid receptor antagonist properties of naltrexone and 6 beta-naltrexol in morphine-naïve and morphine-dependent mice.

It has been proposed that on chronic morphine treatment the micro-opioid receptor becomes constitutively active, and as a consequence, the opioid withdrawal response arises from a reduction in the level of this constitutively active receptor. In support of this, the putative micro-opioid receptor inverse agonist naltrexone has been shown to precipitate more severe withdrawal behavior in mice than the putative neutral receptor antagonist 6 beta-naltrexol. In the present study naltrexone and 6 beta-naltrexol were compared in NIH Swiss mice to test the hypothesis that their differential ability to precipitate withdrawal is due to differences in their in vivo opioid receptor antagonist potencies caused by differential access to micro-opioid receptors in the central nervous system and not necessarily by intrinsic differences in their opioid receptor activity. In naïve mice both compounds had similar potencies to antagonize morphine-induced antinociception in the hot plate and warm-water tail-withdrawal assays when measured under equilibrium conditions and afforded similar calculated apparent in vivo micro-opioid receptor affinities. In morphine-dependent mice both compounds precipitated withdrawal jumping but naltrexone was between 10- and 100-fold more potent than 6 beta-naltrexol. A similar potency difference was seen for other withdrawal behaviors. Both naltrexone and 6 beta-naltrexol at 1 mg/kg reversed antinociception induced by the long-lasting micro-opioid receptor agonist BU72 in the warm-water tail-withdrawal assay, but antagonism by naltrexone was 6-fold more rapid in onset at equal doses. Since the compounds have similar affinity for the micro-opioid receptor in vivo, the results suggest that the differences observed between the ability of naltrexone and 6 beta-naltrexol to precipitate withdrawal in the mouse may be explained by differential onset of receptor antagonist action.

Effects of intrathecally administered nociceptin/orphanin FQ in monkeys: behavioral and mass spectrometric studies.

Nociceptin/orphanin FQ (N/OFQ) is a heptadecapeptide that is an endogenous ligand for the N/OFQ peptide (NOP) receptor. The aim of this study was to investigate the behavioral responses of N/OFQ and its major fragment N/OFQ(2-17) in monkeys following i.t. administration. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to quantify the amounts of N/OFQ and N/OFQ(2-17) in the cerebrospinal fluid at specific time points when effects of i.t. N/OFQ were sustained and disappeared. Intrathecal administration of N/OFQ dose dependently (10-100 nmol) produced long-lasting antinociception against a noxious stimulus, 50 degrees C water, and did not elicit itch/scratching responses in monkeys. Subcutaneous pretreatment with a selective NOP receptor antagonist, (+)J-113397 [(1-[3R,4R)-1-cyclooctymethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3,-dihydro-2H-benzimidazol-2-one] (0.1 mg/kg), completely blocked i.t. N/OFQ (100 nmol)-induced antinociception. In contrast, a classic opioid receptor antagonist, naltrexone (0.01 and 1 mg/kg), failed to reverse i.t. N/OFQ-induced antinociception. MALDI-TOF-MS showed that the amount of N/OFQ(2-17) was 4-fold higher than that of N/OFQ at 1.5 h after i.t. administration of 100 nmol N/OFQ. Intrathecal N/OFQ-induced antinociception disappeared at 4.5 h, which corresponded to nearly undetectable cerebrospinal fluid levels of N/OFQ. No other metabolite of N/OFQ was detected at appreciable levels at either the 1.5- or 4.5-h time points. Although significant amounts of N/OFQ(2-17) were detected at the 1.5- and 4.5-h time points, 100 nmol N/OFQ(2-17) i.t. was inactive in changing the monkeys' nociceptive threshold. These results provide the first functional evidence of spinal N/OFQ-induced antinociception in primates and indicate that activation of spinal NOP receptors may be a potential target for spinal analgesics.

Endogenous opioids upregulate brain-derived neurotrophic factor mRNA through delta- and micro-opioid receptors independent of antidepressant-like effects.

Systemic administration of delta-opioid receptor (DOR) agonists decreases immobility in the forced swim test (FST) and increases brain-derived neurotrophic factor (BDNF) mRNA expression in rats, indicating that DOR agonists may have antidepressant-like effects. The aim of this study was to investigate the effects of central administration of endogenous opioid peptides on behavior in the FST and on brain BDNF mRNA expression in rats. Effects of endogenous opioids were compared with those produced by intracerebroventricular administration of a selective non-peptidic DOR agonist (+)BW373U86. Antidepressant-like effects were measured by decreased immobility in the FST. BDNF mRNA expression was determined by in situ hybridization. Centrally administered (+)BW373U86 decreased immobility and increased BDNF mRNA expression in the frontal cortex through a DOR-mediated mechanism, because these effects were blocked by the DOR antagonist naltrindole, but not by the micro-opioid receptor (MOR) antagonist naltrexone (NTX) or the kappa-opioid receptor antagonist nor-binaltorphimine. Of all the endogenous opioids tested, only leu- and met-enkephalin produced behavioral effects like those of (+)BW373U86 in the FST. Unlike (+)BW373U86, the enkephalins upregulated BDNF mRNA expression in the hippocampus through DOR- and MOR-mediated mechanisms. beta-Endorphin, endomorphin-1 and endomorphin-2 significantly increased BDNF mRNA levels in the frontal cortex, hippocampus and amygdala without reducing immobility; and most of these effects were reversed by NTX. This study is the first to provide evidence that endogenous opioids can upregulate BDNF mRNA expression through the DOR and MOR, and that leu- and met-enkephalin have similar pharmacological profiles to synthetic DOR agonists in producing antidepressant-like effects.

Differential in vivo potencies of naltrexone and 6beta-naltrexol in the monkey.

6beta-Naltrexol is the major metabolite of the opioid receptor antagonist, naltrexone, in humans. However, there are no functional studies of 6beta-naltrexol in primates. The aim of this study was to compare the in vitro and in vivo potencies of naltrexone and 6beta-naltrexol in rhesus monkeys. Affinity and potency were determined using radioligand displacement and stimulation of 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding in monkey brain membranes. In vivo apparent pA(2) analysis was applied to compare the mu-opioid receptor (MOR) antagonist potency of both compounds in nondependent monkeys. In addition, the potencies of both compounds were determined in precipitating withdrawal manifested by increased respiratory parameters in acute morphine-dependent monkeys. In vitro assays revealed that naltrexone displayed 2-fold higher affinity and potency than 6beta-naltrexol for the MOR binding site and for MOR agonist-stimulated [(35)S]GTPgammaS binding, respectively. 6beta-Naltrexol (0.32-3.2 mg/kg) dose-dependently produced parallel rightward shifts of the dose-response curve of alfentanil-induced antinociception. Nevertheless, the apparent pA(2) value of 6beta-naltrexol (6.5) was 100-fold less potent than that of naltrexone (8.5) determined previously. 6beta-Naltrexol was also less potent than naltrexone in antagonizing other MOR-mediated effects including respiratory depression and itch/scratching. Naltrexone (0.0032-0.032 mg/kg) and 6beta-naltrexol (0.32-3.2 mg/kg) retained the same potency difference in precipitating withdrawal to a similar degree. Furthermore, 6beta-naltrexol failed to block naltrexone-precipitated withdrawal in morphine-dependent monkeys. These results indicate that naltrexone and 6beta-naltrexol display similar pharmacological actions with a large in vivo potency difference in monkeys such that 6beta-naltrexol may play a minimal role in the therapeutic or antagonist effects of naltrexone in primates.

How best to fight that nasty itch - from new insights into the neuroimmunological, neuroendocrine, and neurophysiological bases of pruritus to novel therapeutic approaches.

While the enormous clinical and psychosocial importance of pruritus in many areas of medicine and the detrimental effects of chronic 'itch' on the quality of life of an affected individual are widely appreciated, the complexity of this sensation is still often grossly underestimated. The current Controversies feature highlights this complexity by portraying pruritus as a truly interdisciplinary problem at the crossroads of neurophysiology, neuroimmunology, neuropharmacology, protease research, internal medicine, and dermatology, which is combated most successfully if one keeps the multilayered nature of 'itch' in mind and adopts a holistic treatment approach - beyond the customary, frequently frustrane monotherapy with histamine receptor antagonists. In view of the often unsatisfactory, unidimensional, and altogether rather crude standard instruments for pruritus management that we still tend to use in clinical practice today, an interdisciplinary team of pruritus experts here critically examines recent progress in pruritus research that future itch management must take into consideration. Focusing on new insights into the neuroimmunological, neuroendocrine, and neurophysiological bases of pruritus, and discussing available neuropharmacological tools, specific research avenues are highlighted, whose pursuit promises to lead to novel, and hopefully more effective, forms of pruritus management.

Antinociceptive, hypothermic, hypotensive, and reinforcing effects of a novel neurotensin receptor agonist, NT69L, in rhesus monkeys.

Neurotensin (NT) is a tridecapeptide found in the nervous system, as well as elsewhere in the body. It has anatomic and functional relationships to dopaminergic neurons in brain. NT has been implicated in the actions of antipsychotic drugs and psychostimulants, and animal studies suggest that neurotensin directly injected into brain has reinforcing effects. Previously, we showed that one of our brain-penetrating analogs of neurotensin, NT69L (N-methyl-L-Arg, L-Lys, L-Pro, L-neo-Trp, L-tert-Leu, L-Leu), has many pharmacological effects in rats including antinociception, hypothermia, and blockade of the hyperactivity caused by psychostimulants (cocaine, D-amphetamine, and nicotine). Since these studies in rats suggest that this compound may have clinical use in humans, we were interested to know what effects NT69L had in primates. NT69L caused a potent antinociceptive effect against capsaicin (0.1 mg)-induced allodynia in 46 degrees C water in rhesus monkeys, inducing 40% of the maximal possible effect at an intravenous dosage of 0.03 mg/kg; its hypotensive effects precluded evaluation of higher dosages. Core temperature measured by rectal probe was modestly reduced at 0.01 and 0.03 mg/kg. In an intravenous self-administration procedure, NT69L was without reinforcing effects at any dose, including those that caused other pharmacological effects, and did not alter cocaine-maintained behavior when administered as a pretreatment.

Characterization of the complex morphinan derivative BU72 as a high efficacy, long-lasting mu-opioid receptor agonist.

The development of buprenorphine as a treatment for opiate abuse and dependence has drawn attention to opioid ligands that have agonist actions followed by long-lasting antagonist actions. In a search for alternatives to buprenorphine, we discovered a bridged pyrrolidinomorphinan (BU72). In vitro, BU72 displayed high affinity and efficacy for mu-opioid receptors, but was also a partial delta-opioid receptor agonist and a full kappa-opioid receptor agonist. BU72 was a highly potent and long-lasting antinociceptive agent against both thermal and chemical nociception in the mouse and against thermal nociception in the monkey. These effects were prevented by mu-, but not kappa- or delta-, opioid receptor antagonists. Once the agonist effects of BU72 had subsided, the compound acted to attenuate the antinociceptive action of morphine. BU72 is too efficacious for human use but manipulation to reduce efficacy could provide a lead to the development of a treatment for opioid dependence.

The role of central mu opioid receptors in opioid-induced itch in primates.

Pruritus (itch sensation) is a significant clinical problem. The aim of this study was to elucidate the roles of opioid receptor types and the site of action in opioid-induced itch in monkeys. Observers who were blinded to the conditions counted scratching after administration of various drugs. Intravenous (i.v.) administration of mu opioid receptor (MOR) agonists (fentanyl, alfentanil, remifentanil, and morphine) evoked scratching in a dose- and time-dependent manner. However, the kappa opioid agonist U-50488H [trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-cyclohexyl)-benzeneacetamide] and delta opioid agonist SNC80 [(+)-4-[(alphaR)-alpha-[2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl]-3-methoxybenzyl]-N,N-diethylbenzamide] did not increase scratching. Intrathecal (i.t.) administration of peptidic MOR agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO, 0.00032-0.01 mg) evoked scratching, but i.v. DAMGO (0.01-1 mg/kg) did not increase scratching. A similar difference between i.t. and i.v. effectiveness was seen with morphine. Antagonist studies revealed that i.v. administration of an opioid receptor antagonist (naltrexone, 0.0032-0.1 mg/kg) dose dependently attenuated scratching induced by i.v. fentanyl (0.018 mg/kg) or morphine (1 mg/kg). However, a peripherally selective opioid antagonist (quaternary naltrexone, 0.0032-0.32 mg/kg) did not block i.v. fentanyl- or morphine-induced scratching. Moreover, a histamine antagonist (diphenhydramine, 0.1-10 mg/kg), failed to attenuate scratching induced by i.t. morphine (0.032 mg) or i.v. morphine (1 mg/kg). Pretreatment with a selective MOR antagonist (clocinnamox, 0.1 mg/kg), but not kappa or delta opioid antagonists (nor-binaltorphimine or naltrindole), blocked i.t. morphine-induced scratching. Together, these data suggest that MOR, not other opioid receptor types or histamine, mediates scratching evoked by opioid analgesics. More important, this study provides in vivo pharmacological evidence that activation of central MOR plays an important role in opioid-induced itch in primates.

Characterization of scratching responses in rats following centrally administered morphine or bombesin.

The aim of this study was to characterize scratching behavior elicited by central administration of morphine or bombesin in rats, and to determine the role of opioid receptors in scratching induced by both pruritogenic agents. Central administration included intracisternal (i.c.), intrathecal (i.t.), and intracerebroventricular (i.c.v.) routes. Scratching events made with hind paws were counted by observers blinded to treatment conditions. Intracisternal morphine (0.01-0.1 microg) produced dose-dependent increases in scratching; the maximum response to i.c. morphine 0.1 microg was approximately 500 scratches within a 1-hour period. Neither i.t. nor i.c.v. morphine significantly increased scratching. Bombesin (0.01-0.32 microg) elicited robust scratching following i.c. administration. The maximum response to i.c. bombesin 0.32 microg was approximately 4000 scratches within a 1-hour period. Both i.t. and i.c.v. bombesin produced profound scratching at similar doses. Antagonist studies confirmed that mu-opioid receptors selectively mediate i.c. morphine-induced scratching. However, selective mu-, kappa-, and delta-opioid antagonists did not attenuate i.c. bombesin-induced scratching. These results demonstrate that morphine and bombesin elicit scratching through different receptor mechanisms, at different central sites, and to different degrees.

Ultra-long antagonism of kappa opioid agonist-induced diuresis by intracisternal nor-binaltorphimine in monkeys.

Kappa opioid receptor (KOR) agonists such as U-50488H and bremazocine are analgesics and diuretics. In monkeys, the selective KOR antagonist, nor-binaltorphimine (nor-BNI), produces a long-lasting antagonism of the antinociceptive effects of U-50488H but not those of bremazocine, suggesting that KOR-mediated antinociception may occur through two distinct KORs. The aim of this study was to characterize the antagonist effect of nor-BNI against the diuretic effects of U-50488H and bremazocine in monkeys. Urine outputs were collected over 3 h subsequent to i.m. administration of KOR agonists. Both U-50488H (0.032-1 mg/kg) and bremazocine (0.00032-0.01 mg/kg) dose-dependently increased urine output and the diuretic effect reached a plateau at higher doses. The maximum effect of either U-50488H or bremazocine was approximately 15 ml/kg/3 h of urine. Pretreatment with intracisternal nor-BNI 0.32 mg significantly blocked both U-50488H (0.18 mg/kg)- and bremazocine (0.0032 mg/kg)-induced diuresis for 20 weeks. However, the same dose of nor-BNI 0.32 mg given subcutaneously was not effective. These results demonstrate that central KOR mediate KOR agonist-induced diuresis in monkeys. More important, this study provides functional evidence for a homogenous population of KOR underlying KOR-mediated diuresis and illustrates a unique pharmacological profile of nor-BNI-induced ultra-long KOR antagonism in vivo.

Effect of opioid receptor antagonists on hypothalamic-pituitary-adrenal activity in rhesus monkeys.

Some opioid antagonists increase the release of adrenocorticotropic hormone (ACTH) and cortisol in humans and, therefore, may indicate that endogenous opioids modulate hypothalamic-pituitary-adrenal axis activity. The type of opioid receptor that may be related to these endocrine effects is unknown. The purpose of this experiment was to evaluate the ability of different opioid antagonists to increase ACTH and cortisol plasma levels in rhesus monkeys. Eight monkeys received intramuscular injections of various antagonists: 0.0032-1.0 mg/kg naltrexone, 0.1-3.2 mg/kg naltrindole (delta-selective), 0.032-0.32 mg/kg clocinnamox (mu-selective), and 1-3.2 mg/kg nor-binaltorphimine (kappa-selective). Naltrexone, 0.1-1.0 mg/kg, increased ACTH levels, whereas naltrindole and clocinnamox failed to increase ACTH levels. Nor-binaltorphimine, 1-3.2 mg/kg, increased ACTH concentrations on the day of injection, but not at a time when other assays continue to demonstrate kappa-antagonism (24 h). Cortisol concentrations generally followed the same pattern as the ACTH concentrations, but the incremental differences in cortisol release between doses were less clear. Thus, opioid modulation of ACTH and cortisol plasma levels is not clearly associated with a particular opioid receptor. Although the kappa-antagonist increased ACTH and cortisol release on the day of injection, some evidence suggests that this endocrine effect may be due to mechanisms other than those mediated by the kappa-receptor. Alternatively, the naltrexone-induced increase of ACTH and cortisol plasma levels may be caused by activity at multiple opioid receptors or some uncharacterized receptor. Finally, the increased release of ACTH and cortisol may be a response to naltrexone's aversive properties.