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Opioid Agonists (opioid + agonist)
Selected AbstractsThe 14-Alkyl- and 14-Alkenyl-5, -methylindolomorphinan Series Provide , -Selective Partial Opioid AgonistsHELVETICA CHIMICA ACTA, Issue 3 2003Peter Grundt A series of 14, -alkyl- and 14, -alkenyl-5, -methylindolomorphinans was synthesized and evaluated in opioid binding and functional assays. While being relatively nonselective in binding assays, the 14-cinnamyl and 14-isopentyl members showed selective opioid , -receptor partial agonist activity in [35S]GTP,S assays. [source] The neurophysiology of dyspneaJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 6 2008Matthew Scott Mellema DVM Abstract Objective , To review the human and veterinary literature regarding the neurophysiology of dyspnea and to provide evidence for the beneficial effects of several novel therapies aimed at the alleviation of dyspneic sensations. Data Sources , Data sources included scientific reviews, case reports, original research publications, and recent research conference proceedings. Human Data Synthesis , The use of blood oxygenation level-dependent functional magnetic resonance imaging technology has revealed that the brain regions activated by air hunger in humans are also those activated by fear, pain, and thirst perception. In human subjects, it has been found that agents known to enhance the firing of pulmonary slowly adapting receptors (SARs) can alleviate the sensation of dyspnea without altering central respiratory drive. Several small studies have also shown that nebulized opioids can reduce the sensation of dyspnea apparently via activation of peripheral opioid receptors in the lung. Veterinary Data Synthesis , There are several animal models relevant to both small and large animal clinical patient populations. Treatment of rats with a nebulized SAR sensitizing agent (furosemide) enhances SAR firing in response to lung inflation. Behavioral escape responses to airway occlusion are reduced in lightly anesthetized cats when treated with nebulized furosemide. Opioid agonists have been shown to inhibit the release of acetylcholine and other mediators from the airways of dogs and guinea pigs. Studies using a goat model with bilateral destruction of the pre-Bötzinger Complex do not support current paradigms of air hunger origination. Conclusions , Veterinary patients may benefit from an approach to dyspnea that incorporates an understanding of the origins of the unpleasant sensations associated with the condition. Several novel therapies have shown promise in alleviating dyspneic sensations without altering respiratory drive. Further study is needed to determine the safety and efficacy of these therapies in veterinary patients. [source] Constitutive opioid receptor activation: a prerequisite mechanism involved in acute opioid withdrawalADDICTION BIOLOGY, Issue 2 2005E Freye The opioid receptor antagonist naltrexone, which is used in detoxification and rehabilitation programmes in opioid addicts, can precipitate opioid withdrawal symptoms even in patients who have no opioid present. We tested the hypothesis that in order to precipitate withdrawal, opioids need to convert the inactive opioid receptor site via protein kinase C into a constitutively active form on which the antagonist precipitates withdrawal. Acute abstinence symptoms were induced by the potent opioid receptor agonist sufentanil (21?,g/kg), given for 6 days, which was followed by the antagonist naltrexone (20?,g/kg i.v.) in the awake trained canine (n,=,10). Abrupt displacement of opioid binding resulted in acute withdrawal symptoms: increase in blood pressure, heart rate, increase in amplitude height of somatosensory evoked potential, reduced tolerance to colon distention and a significant increase in grading of vegetative variables (restlessness, panting, thrashing of the head, whining, yawning, gnawing, salivation and/or rhinorrhoea, mydriasis, stepping of extremities and vomiting). Following a washout period of 14 days, the same animals were given the highly specific protein kinase C inhibitor H7 (250?,g/kg) prior to the same dosages of sufentanil and naltrexone. Such pretreatment was able to either attenuate or completely abolish the acute withdrawal symptoms. The data suggest that for precipitation of withdrawal, intracellular phosphorylation is a prerequisite in order to activate the opioid ,-receptor. In such a setting, naltrexone acts like an ,inverse agonist? relative to the action of the antagonist on a non-preoccupied receptor site not being exposed previously to a potent opioid agonist. [source] Hypoxia modulates cholinergic but not opioid activation of G proteins in rat hippocampusHIPPOCAMPUS, Issue 10 2007V.S. Hambrecht Abstract Intermittent hypoxia, such as that associated with obstructive sleep apnea, can cause neuronal death and neurobehavioral dysfunction. The cellular and molecular mechanisms through which hypoxia alter hippocampal function are incompletely understood. This study used in vitro [35S]guanylyl-5,- O -(,-thio)-triphosphate ([35S]GTP,S) autoradiography to test the hypothesis that carbachol and DAMGO activate hippocampal G proteins. In addition, this study tested the hypothesis that in vivo exposure to different oxygen (O2) concentrations causes a differential activation of G proteins in the CA1, CA3, and dentate gyrus (DG) regions of the hippocampus. G protein activation was quantified as nCi/g tissue in CA1, CA3, and DG from rats housed for 14 days under one of three different oxygen conditions: normoxic (21% O2) room air, or hypoxia (10% O2) that was intermittent or sustained. Across all regions of the hippocampus, activation of G proteins by the cholinergic agonist carbachol and the mu opioid agonist [D-Ala2, N-Met-Phe4, Gly5] enkephalin (DAMGO) was ordered by the degree of hypoxia such that sustained hypoxia > intermittent hypoxia > room air. Carbachol increased G protein activation during sustained hypoxia (38%), intermittent hypoxia (29%), and room air (27%). DAMGO also activated G proteins during sustained hypoxia (52%), intermittent hypoxia (48%), and room air (43%). Region-specific comparisons of G protein activation revealed that the DG showed significantly less activation by carbachol following intermittent hypoxia and sustained hypoxia than the CA1. Considered together, the results suggest the potential for hypoxia to alter hippocampal function by blunting the cholinergic activation of G proteins within the DG. © 2007 Wiley-Liss, Inc. [source] In Vivo Modulation of Post-Spike Excitability in Vasopressin Cells by ,-Opioid Receptor ActivationJOURNAL OF NEUROENDOCRINOLOGY, Issue 8 2000C. H. Brown Abstract An endogenous ,-opioid agonist reduces the duration of phasic bursts in vasopressin cells. Non-synaptic post-spike depolarizing after-potentials underlie activity during bursts by increasing post-spike excitability and ,-receptor activation reduces depolarizing after-potential amplitude in vitro. To investigate the effects of ,-opioids on post-spike excitability in vivo, we analysed extracellular recordings of the spontaneous activity of identified supraoptic nucleus vasopressin cells in urethane-anaesthetized rats infused with Ringer's solution (n = 17) or the ,-agonist, U50,488H (2.5 µg/h at 0.5 µl/h; n = 23), into the supraoptic nucleus over 5 days. We plotted the mean hazard function for the interspike interval distributions as a measure of the post-spike excitability of these cells. Following each spike, the probability of another spike firing in vasopressin cells recorded from U50,488H infused nuclei was markedly reduced compared to Ringer's treated vasopressin cells. To determine whether U50,488H could reduce post-spike excitability in cells that displayed spontaneous phasic activity, we infused U50,488H (50 µg/h at 1 µl/h, i.c.v.), for 1,12 h while recording vasopressin cell activity. Nine of 10 vasopressin cells were silenced by i.c.v. U50,488H 15 ± 5 min into the infusion. Six cells exhibited spontaneous phasic activity before U50,488H infusion and recordings from three of these phasic cells were maintained until activity recovered; during U50,488H infusion, the activity of these three cells was irregular. Generation of the mean hazard function before and during U50,488H infusion revealed a reduction in post-spike excitability during U50,488H infusion. Thus, ,-receptor activation reduces post-spike excitability in vivo; this may reflect inhibition of depolarizing after-potentials and may thus underlie the reduction in burst duration of vasopressin cells caused by an endogenous ,-agonist in vivo. [source] Opioids in the Hypothalamic Paraventricular Nucleus Stimulate Ethanol IntakeALCOHOLISM, Issue 2 2010Jessica R. Barson Background:, Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists. Methods:, Sprague,Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the ,-receptor agonist [d -Ala2,N -Me-Phe4,Gly5 -ol]-Enkephalin (DAMGO), ,-receptor agonist d -Ala-Gly-Phe-Met-NH2 (DALA), or ,-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN. Results:, A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the ,-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the ,-agonist U-50,488H, which decreased ethanol intake, and the ,-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip. Conclusions:, The ,-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the ,-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the ,- and ,-receptors, respectively. These results suggest that enkephalin via the ,-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the ,-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle. [source] Opioid dysphoria in three dogsJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 1 2006Erik H. Hofmeister DVM Abstract Objective: To describe the clinical manifestations and response to management of opioid dysphoria in 3 dogs. Case summary: Three dogs being managed for post-operative pain were evaluated. All 3 dogs had been managed with various opioids including morphine, hydromorphone, and fentanyl following the surgical procedure. The 3 dogs exhibited vocalization that did not respond to interaction and did not change with administration of analgesic and anxiolytic agents. The dogs were treated with naloxone and, within 5 minutes of its administration, ceased vocalizing, and became aware and interactive with their environment. Further pain management consisted of non-steroidal anti-inflammatory medications, alpha-2 (,2) receptor agonists or the partial ,-receptor opioid agonist, buprenorphine. New and unique information provided: Vocalization and lack of response to interaction with humans are clinical signs which can be seen in dogs with opioid dysphoria, and generally are not responsive to analgesics or sedation. Reversal with naloxone results in rapid resolution of vocalization and opioid-induced dysphoria. [source] Novel pharmacology: asimadoline, a ,-opioid agonist, and visceral sensationNEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2008M. Camilleri Abstract, Asimadoline is a potent ,-opioid receptor agonist with a diaryl acetamide structure. It has high affinity for the , receptor, with IC50 of 5.6 nmol L,1 (guinea pig) and 1.2 nmol L,1 (human recombinant), and high selectively with , : , : , binding ratios of 1 : 501 : 498 in human recombinant receptors. It acts as a complete agonist in in vitro assay. Asimadoline reduced sensation in response to colonic distension at subnoxious pressures in healthy volunteers and in irritable bowel syndrome (IBS) patients without alteration of colonic compliance. Asimadoline reduced satiation and enhanced the postprandial gastric volume (in female volunteers). However, there were no significant effects on gastrointestinal transit, colonic compliance, fasting or postprandial colonic tone. In a clinical trial in 40 patients with functional dyspepsia (Rome II), asimadoline did not significantly alter satiation or symptoms over 8 weeks. However, asimadoline, 0.5 mg, significantly decreased satiation in patients with higher postprandial fullness scores, and daily postprandial fullness severity (over 8 weeks); the asimadoline 1.0 mg group was borderline significant. In a clinical trial in patients with IBS, average pain 2 h post- on-demand treatment with asimadoline was not significantly reduced. Post hoc analyses suggest that asimadoline was effective in mixed IBS. In a 12-week study in 596 patients, chronic treatment with 0.5 mg and 1.0 mg asimadoline was associated with adequate relief of pain and discomfort, improvement in pain score and number of pain-free days in patients with IBS-D. The 1.0 mg dose was also efficacious in IBS-alternating. There were also weeks with significant reduction in bowel frequency and urgency. Asimadoline has been well tolerated in human trials to date. [source] Inpatient Initiation of Buprenorphine Maintenance vs.THE AMERICAN JOURNAL ON ADDICTIONS, Issue 1 2006Detoxification: Can Retention of Opioid-Dependent Patients in Outpatient Counseling Be Improved? Buprenorphine-naloxone is an office-based opioid agonist released in 2003 in the United States for the maintenance of heroin- and other opioid-dependent patients. Concern has been raised that the medication will distract or otherwise inhibit patients from participating in a holistic recovery program or abstinence-based counseling. Using a retrospective chart review, the first thirty opioid-dependent patients induced on buprenorphine maintenance therapy in an inpatient detoxification unit were compared to thirty age- and gender-matched patients who underwent detoxification (with a tramadol taper) and referral to intensive outpatient treatment. The clinical outcomes were a comparison of completion rates for an intensive outpatient program (IOP) and retention in treatment after twelve weeks of aftercare therapy. Patients induced on buprenorphine maintenance over three days had similar relief of withdrawal symptoms to patients detoxified from opioids over five days with tramadol. Patients maintained on buprenorphine had a markedly increased initiation of IOP and remained in outpatient treatment longer than patients who were detoxified (8.5 wks vs. 0.4 wks, p<0.001). This study indicates that induction and maintenance on buprenorphine may be more effective than detoxification for engaging and retaining patients in abstinence-based comprehensive outpatient addiction treatment. [source] A Double-blind Randomized Clinical Trial Evaluating the Analgesic Efficacy of Ketorolac versus Butorphanol for Patients with Suspected Biliary Colic in the Emergency DepartmentACADEMIC EMERGENCY MEDICINE, Issue 8 2008Jon C. Olsen MD Abstract Objectives:, Patients presenting to the emergency department (ED) with suspected biliary colic often require intravenous (IV) analgesia. The choice of IV analgesia typically includes opioids and ketorolac. Although ultrasound (US) is the initial diagnostic study in these patients, nondiagnostic scans and a high clinical suspicion may require the patient to undergo hepatobiliary scintigraphy (HIDA). Opioids such as morphine interfere with the HIDA scan and thus may limit its value as an analgesic in the ED for these patients. Analgesics that do not interfere with HIDA scanning include ketorolac and butorphanol, an opioid agonist,antagonist. This study evaluates the efficacy of IV ketorolac compared to butorphanol for the treatment of biliary colic pain in the ED. Methods:, Between June 2005 and February 2007, a convenience sample of patients presenting to the ED with abdominal pain suspected to be biliary colic were randomized to receive either 30 mg of IV ketorolac or 1 mg of IV butorphanol. Pain level was assessed using a 1 to 10 "faces" visual analog pain scale initially, as well as 15 and 30 minutes after medication infusion. Side effect profiles and the need for rescue analgesia were also assessed. Patients and clinicians were blinded to the study drug given. Results:, Forty-six patients were enrolled in the study. Both groups had similar demographics and baseline pain scores. The mean (±standard deviation [SD]) pain score in the butorphanol group decreased from 7.1 (±1.7) to 2.1 (±2.2) after 30 minutes. The mean (±SD) pain score in the ketorolac group decreased from 7.4 (±2.0) to 3.1 (±3.3) after 30 minutes. Both groups had similar needs for rescue analgesia. Side effects included dizziness and sedation with butorphanol and nausea with ketorolac. Conclusions:, Although limited by small sample size and convenience sample, this study demonstrates that both ketorolac and butorphanol provide pain relief in biliary colic. Both agents should be considered reasonable options in the ED treatment of biliary colic, especially in patients that may undergo HIDA. [source] Potent Opioid Peptide Agonists Containing 4,-[N -((4,-phenyl)-phenethyl)carboxamido]phenylalanine (Bcp) in Place of TyrCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2008Grazyna Weltrowska Analogues of the opioid peptides H-Tyr-c[d -Cys-Gly-Phe(pNO2)- d -Cys]NH2 (non-selective), H-Tyr- d -Arg-Phe-Lys-NH2 (,-selective) and dynorphin A(1-11)-NH2 (,-selective) containing 4,-[N -((4,-phenyl)-phenethyl)carboxamido]phenylanine (Bcp) in place of Tyr1 were synthesized. All three Bcp1 -opioid peptides retained high , opioid receptor binding affinity, but showed very significant differences in the opioid receptor selectivity profiles as compared with the corresponding Tyr1 -containing parent peptides. The cyclic peptide H-Bcp-c[d -Cys-Gly-Phe(pNO2)- d -Cys]NH2 turned out to be an extraordinarily potent, ,-selective opioid agonist, whereas the Bcp1 -analogue of dynorphin A(1-11)-NH2 displayed partial agonism at the , receptor. The obtained results suggest that the large biphenylethyl substituent contained in these compounds may engage in a hydrophobic interaction with a receptor subsite and thereby may play a role in the ligand's ability to induce a specific receptor conformation or to bind to a distinct receptor conformation in a situation of conformational receptor heterogeneity. [source] Challenges to antagonist blockade during sustained-release naltrexone treatmentADDICTION, Issue 9 2010Nikolaj Kunøe ABSTRACT Aims Naltrexone is a competitive opioid antagonist that effectively blocks the action of heroin and other opioid agonists. Sustained-release naltrexone formulations are now available that provide long-acting opioid blockade. This study investigates the use of heroin and other opioids among opioid-dependent patients receiving treatment with long-acting naltrexone implants, their subjective experience of drug ,high' after opioid use, and factors associated with opioid use. Methods Participants (n = 60) were opioid-dependent patients receiving treatment with naltrexone implants. Outcome data on substance use, drug ,high', depression and criminal activity were collected over a 6-month period. Blood samples were taken to monitor naltrexone plasma levels, and hair samples to verify self-reported opioid use. Findings More than half [n = 34 or 56%; 95% confidence interval (CI) 44,68%)] the patients challenged the blockade with illicit opioids during the 6-month treatment period; 44% (n = 26; 95% CI 32,56%) were abstinent from opioids. Mean opioid use was reduced from 18 [standard deviation (SD)13] days during the month preceding treatment to 6 days (SD 11) after 6 months. Of the respondents questioned on opioid ,high' (n = 31), nine patients (30%; 95% CI 16,47%) reported partial drug ,high' following illicit opioid use, and three (12%; 95% CI 3,26%) reported full ,high'. Opioid use was associated with use of non-opioid drugs and criminal behaviour. Conclusions Challenging naltrexone blockade with heroin on at least one occasion is common among sustained-release naltrexone patients, but only a minority of patients use opioids regularly. Challenges represent a warning sign for poor outcomes and often occur in the context of polydrug use and social adjustment problems. [source] Opioids and the skin , where do we stand?EXPERIMENTAL DERMATOLOGY, Issue 5 2009Paul L. Bigliardi Abstract:, The common ectodermal origin of the skin and nervous systems can be expected to predict likely interactions in the adult. Over the last couple of decades much progress has been made to elucidate the nature of these interactions, which provide multidirectional controls between the centrally located brain and the peripherally located skin and immune system. The opioid system is an excellent example of such an interaction and there is growing evidence that opioid receptors (OR) and their endogenous opioid agonists are functional in different skin structures, including peripheral nerve fibres, keratinocytes, melanocytes, hair follicles and immune cells. Greater knowledge of these skin-associated opioid interactions will be important for the treatment of chronic and acute pain and pruritus. Topical treatment of the skin with opioid ligands is particularly attractive as they are active with few side effects, especially if they cannot cross the blood,brain barrier. Moreover, cutaneous activation of the opioid system (e.g. by peripheral nerves, cutaneous and immune cells, especially in inflamed and damaged skin) can influence cell differentiation and apoptosis, and thus may be important for the repair of damaged skin. While many of the pieces of this intriguing puzzle remain to be found, we attempt in this review to weave a thread around available data to discuss how the peripheral opioid system may impact on different key players in skin physiology and pathology. [source] Update in the pharmaceutical therapy of the irritable bowel syndromeINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 4 2004F. Thielecke Summary The therapeutic management of the irritable bowel syndrome (IBS) is ineffective and not satisfying either patients or practitioners. Research in functions of the enteric nervous system and its interaction with the central nervous system is the basis for the development of emerging pharmaceuticals in therapy of the IBS. These pharmaceuticals include agents such as opioid agonists, psychotropic agents and particularly serotonin receptor modulators. These novel pharmaceuticals aim to provide a more comprehensive approach in the therapy of the IBS and will serve both patients and practitioners. So far, the US Food and Drug Administration has approved two agents specifically for the treatment of the IBS, both belonging to the group of serotonin receptor modulators. However, questions remain whether a single therapy is sufficient in the management of IBS because this disease is influenced by biological and psychological as well as cultural and social factors. [source] The potential for ,-opioid receptor agonists to be anti-emetic in humans: a review of clinical dataACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 2 2010KEVIN D. JOHNSTON In animal models of vomiting, ,-opioid (MOP, OP3) receptors mediate both emesis and anti-emesis. ,-receptors within the blood,brain barrier, mediating anti-emesis, are more rapidly accessible to lipid-soluble ,-opioid receptor agonists such as fentanyl than to morphine, and fentanyl has broad-spectrum anti-emetic effects in a number of species. Whether a similar situation exists in humans is not known. A search was performed for clinical studies comparing the emetic side effects of opioids administered peri-operatively in an attempt to identify differences between morphine and more lipid-soluble ,-receptor-selective agonists such as fentanyl. Overall, the evidence appears to suggest that fentanyl and other phenylpiperidines are associated with less nausea and vomiting than morphine, but not all studies support this, and fentanyl-like drugs are associated with nausea and vomiting per se. Good evidence, however, exists to show that fentanyl and alfentanil do not cause more nausea and vomiting than the ultra fast-acting remifentanil. Because remifentanil is cleared rapidly post-operatively, such trials suggest that the emetic side effects of fentanyl and alfentanil are minimal. The clinical evidence, although limited, is at least consistent with the possibility that central ,-opioid receptors may mediate anti-emesis in humans. It is possible that the role of ,-opioid agonists in anti-emesis may become clearer in the future as a result of the use of peripheral ,-opioid receptor antagonists. [source] Conformation-activity relationships of cyclo -constrained µ/, opioid agonists derived from the N -terminal tetrapeptide segment of dermorphin/deltorphinJOURNAL OF PEPTIDE SCIENCE, Issue 8 2008Sylwia Rodziewicz-Motowid Abstract The N -terminal tetrapeptide segments of dermorphin (Tyr,D -Ala,Phe,Gly,Tyr,Pro,Ser,NH2) and deltorphin (Tyr,D -Ala,Phe,Asp/Glu,Val,Val,Gly,NH2) are agonists at the opioid receptors µ and ,, respectively. [D -Arg2, Lys4]-dermorphin-(1,4) amide (Tyr,D -Arg,Phe,Lys,NH2, DALDA) and [Dmt1]DALDA (where Dmt is 2,,6,-dimethyltyrosine) are among the most potent and selective µ-agonists reported to date, both in vitro (having picomolar µ receptor affinity) and in vivo. In this communication, conformation-activity studies of the following four cyclic analogs of DALDA are presented and discussed: the lead peptide S2,S4 -cyclo (Tyr,D -Cys,Phe,Cys,NH2), constrained by means of an S4.2S4.4 disulfide between Cys2 and Cys4; its two cis and transC4.2C4.4 -olefinic dicarba analogs, and the product of saturation of them both. They are potent nonselective or moderately µ-selective opioid agonists in vitro. They have been synthesized and tested earlier [Berezowska I, Chung NN, Lemieux C, Wilkes BC, and Schiller PW, Acta Biochim Polon 53, 2006, 73,76]. We have studied their conformations using NMR and molecular dynamics. With major conformational constraints imposed by the 11-membered ring spanning residues 2,4, they show well defined conformations of this ring, while the exocylic Tyr1 and Phe3 side chains still have significant conformational freedom. The more active and selective µ versus , disulfide and saturated dicarba agonists seem to have in common: (i) their ring structures more flexilble than those of the other two and (ii) their ring structures similar to each other and more diverse than those in the other two. Given this and the small size of the peptides having confirmed bioactivity profiles, there is a chance that their conformations determined in solution approach receptor-bound conformations. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Morphine, opioids, and the feline pulmonary vascular bedACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 7 2008A. D. KAYE Background: Opioid-induced vasodepressor responses have been reported in a variety of species and laboratory models. The aim of this study was to ascertain the relative potencies of different clinically relevant opioids compared with traditional vasodepressor agents in the feline pulmonary vascular bed. A second aim was to study the effects of morphine and to identify the receptors involved in the mediation or the modulation of these effects. Methods: This was a prospective vehicle-controlled study involving an intact chest preparation of adult mongrel cats. The effects of various opioids, morphine, fentanyl, remifentanil, sufentanil, and meperidine were compared with other vasodepressor agents. Additionally, the effects of l - N5 -(1-iminoethyl) ornithine hydrochloride (l -NIO) (nitric oxide synthase inhibitor), nimesulide [selective cyclooxygenase (COX)-2 inhibitor], glibenclamide (ATP-sensitive K+ channel blocker), naloxone (non-selective opioid receptor antagonist), and diphenhydramine (histamine H1 -receptor antagonist) were investigated on pulmonary arterial responses to morphine and other selected agonists in the feline pulmonary vascular bed. The systemic pressure and lobar arterial perfusion pressure were continuously monitored, electronically averaged, and recorded. Results: In the cat pulmonary vascular bed of the isolated left lower lobe, morphine, remifentanil, fentanyl, sufentanil, and meperidine induced a dose-dependent moderate vasodepressor response and it appeared that sufentanil was the most potent on a nanomolar basis. The effects of morphine were not significantly altered after administration of l -NIO, nimesulide, and glibenclamide. However, the vascular responses to morphine were significantly attenuated following administration of naloxone and diphenhydramine. Conclusion: The results of the present study suggest that sufentanil appears to have slightly more potency and morphine the least of the five opioid agonists studied on a nanomolar basis. Morphine-induced vasodilatory responses appeared to be mediated or modulated by both opioid receptor and histamine-receptor-sensitive pathways. [source] Opioids in the Hypothalamic Paraventricular Nucleus Stimulate Ethanol IntakeALCOHOLISM, Issue 2 2010Jessica R. Barson Background:, Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists. Methods:, Sprague,Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the ,-receptor agonist [d -Ala2,N -Me-Phe4,Gly5 -ol]-Enkephalin (DAMGO), ,-receptor agonist d -Ala-Gly-Phe-Met-NH2 (DALA), or ,-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN. Results:, A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the ,-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the ,-agonist U-50,488H, which decreased ethanol intake, and the ,-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip. Conclusions:, The ,-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the ,-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the ,- and ,-receptors, respectively. These results suggest that enkephalin via the ,-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the ,-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle. [source] Opioids and the gut: pharmacology and current clinical experienceNEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2004H. U. De Schepper Abstract, This article reviews the pharmacology and physiology of opiate receptors and the current and potential uses of opioid agonists and antagonists in clinical gastroenterology. ,-receptors are involved in motor and sensory functions, and their modulation is established for treatment of diarrhea. ,-antagonists have potential to reverse endogenous (e.g., postoperative ileus) or iatrogenic dysmotility (e.g., opioid bowel dysfunction). Modulation of the function of ,-receptors may be a novel approach to control visceral pain in functional gut disorders. Results of formal testing of novel opioid modulators are keenly awaited. [source] Cellular Actions Of Opioids And Other Analgesics: Implications For Synergism In Pain ReliefCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 7 2000MacDonald J Christie SUMMARY 1. ,-Opioid receptor agonists mediate their central analgesic effects by actions on neurons within brain regions such as the mid-brain periaqueductal grey (PAG). Within the PAG, ,-opioid receptor-mediated analgesia results from inhibition of GABAergic influences on output projection neurons. We have established that ,-opioid receptor activation in the PAG causes a presynaptic inhibition of GABA release that is mediated by activation of a voltage-dependent K+ channel via 12-lipoxygenase (LOX) metabolites of arachidonic acid. 2. At a cellular level, ,-opioid agonists have also been shown to open inwardly rectifying K+ channels, close voltage-gated Ca2+ channels and presynaptically inhibit glutamatergic synaptic transmission in the PAG. 3. The ,-opioid receptor-mediated presynaptic inhibition of GABAergic transmission was abolished by phospholipase A2 inhibitors and non-specific LOX and specific 12-LOX inhibitors. Cyclo-oxygenase (COX) and specific 5-LOX inhibitors did not reduce the inhibitory effects of ,-opioid agonists. 4. The opioid actions on GABAergic transmission were mimicked by arachidonic acid and 12-LOX metabolites, but not 5-LOX metabolites. The efficacy of ,-opioids was enhanced synergistically by treatment of PAG neurons with inhibitors of the other major enzymes responsible for arachidonic acid metabolism, COX and 5-LOX. 5. These results explain a previously described analgesic action of COX inhibitors in the central nervous system that was both independent of prostanoid release and inhibited by opioid receptor antagonists and they also explain the synergistic interaction of opioids with COX inhibitors. These findings also suggest new avenues for the development of centrally active analgesic agents involving combinations of lowered doses of opioids and specific 5-LOX inhibitors. [source] | ||||||||||||||||