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Protein kinase C-mediated mu-opioid receptor phosphorylation and desensitization in rats, and its prevention during early diabetes. Pain 2017; 157:910-921. [PMID: 26713421 DOI: 10.1097/j.pain.0000000000000459] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Painful diabetic neuropathy is associated with impaired opioid analgesia; however, the precise mechanism in sensory neurons remains unclear. This study aimed to identify putative mechanisms involved in modified opioid responsiveness during early streptozotocin-induced diabetes in rats. In this study, we demonstrate that in diabetic animals, impaired peripheral opioid analgesia is associated with a reduction in functional mu-opioid receptor (MOR) G protein coupling. Mu-opioid receptor immunoreactive neurons colocalized with activated forms of protein kinase C (PKC) and with the receptor for advanced glycation end products (RAGE) during streptozotocin-induced diabetes. Moreover, MOR phosphorylation at Thr370 in sensory neurons of diabetic rats, and thus desensitization, was due to RAGE-dependent PKC activation. Importantly, blocking PKC activation using PKC selective inhibitor, silencing RAGE with intrathecal RAGE siRNA, or inhibiting advanced glycation end product (AGE) formation prevented sensory neuron MOR phosphorylation and, consequently, restored MOR G protein coupling and analgesic efficacy. Thus, our findings give the first in vivo evidence of a RAGE-dependent PKC-mediated heterologous MOR phosphorylation and desensitization in sensory neurons under pathological conditions such as diabetic neuropathy. This may unravel putative mechanisms and suggest possible prevention strategies of impaired opioid responsiveness.
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Synergistic combinations of the dual enkephalinase inhibitor PL265 given orally with various analgesic compounds acting on different targets, in a murine model of cancer-induced bone pain. Scand J Pain 2016; 14:25-38. [PMID: 28850427 DOI: 10.1016/j.sjpain.2016.09.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Revised: 09/14/2016] [Accepted: 09/30/2016] [Indexed: 12/19/2022]
Abstract
BACKGROUND The first line pharmacological treatment of cancer pain is morphine and surrogates but a significant pain relief and a reduction of the side-effects of these compounds makes it necessary to combine them with other drugs acting on different targets. The aim of this study was to measure the antinociceptive effect on cancer-induced bone pain resulting from the association of the endogenous opioids enkephalin and non-opioid analgesic drugs. For this purpose, PL265 a new orally active single dual inhibitor of the two degrading enkephalins enzymes, neprilysin (NEP) and aminopeptidase N (APN) was used. It strictly increased the levels of enkephalin at their sites of releases. The selected non-opioid compounds are: gabapentin, A-317491 (P2X3 receptor antagonist), ACEA (CB1 receptor antagonist), AM1241 (CB2 receptor antagonist), JWH-133 (CB2 receptor antagonist), URB937 (FAAH inhibitor), and NAV26 (Nav1.7 channel blocker). METHODS Experiments. Experiments were performed in 5-6 weeks old (26-33g weight) C57BL/6 mice. Cell culture and cell inoculation. B16-F10 melanoma cells were cultured and when preconfluent, treated and detached. Finally related cells were resuspended to obtain a concentration of 2×106 cells/100μL. Then 105 cells were injected into the right tibial medullar cavity. Control mice were treated by killed cells by freezing. Behavioural studies. Thermal withdrawal latencies were measured on a unilatered hot plate (UHP) maintained at 49±0.2°C. Mechanical threshold values were obtained by performing the von Frey test using the "up and down" method. To evaluate the nature (additive or synergistic) of the interactions between PL265 and different drugs, an isobolographic analysis following the method described by Tallarida was performed. RESULTS The results demonstrate the ability of PL265, a DENKI that prevents the degradation of endogenous ENKs, to counteract cancer-induced bone thermal hyperalgesia in mice, by exclusively stimulating peripheral opioid receptors as demonstrated by used of an opioid antagonist unable to enter the brain. The development of such DENKIs, endowed with druggable pharmacokinetic characteristics, such as good absorption by oral route, can be considered as an important step in the development of much needed novel antihyperalgesic drugs. Furthermore, all the tested combinations resulted in synergistic antihyperalgesic effects. As shown here, the greatest synergistic antinociceptive effect (doses could be lowered by 70%) was produced by the combination of PL265 with the P2X3 receptor antagonist (A-317491), cannabinoid CB1 receptor agonist (exogenous, ACEA and endogenous URB937-protected-AEA) and Nav1.7 blocker (NAV26) whose mechanism of action involves the direct activation of the enkephalinergic system. CONCLUSIONS These multi-target-based antinociceptive strategies using combinations of non-opioid drugs with dual inhibitors of enkephalin degrading enzymes may bring therapeutic advantages in terms of efficacy and safety by allowing the reduction of doses of one of the compounds or of both, which is of the utmost interest in the chronic treatment of cancer pain. IMPLICATIONS This article presents synergistic antinociceptive effect produced by the combination of PL265 with non-opioid analgesic drugs acting via unrelated mechanisms. These multi-target-based antinociceptive strategies may bring therapeutic advantages by allowing the reduction of doses, which is of great interest in the chronic treatment of cancer pain.
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Cury Y, Picolo G, Gutierrez VP, Ferreira SH. Pain and analgesia: The dual effect of nitric oxide in the nociceptive system. Nitric Oxide 2011; 25:243-54. [DOI: 10.1016/j.niox.2011.06.004] [Citation(s) in RCA: 180] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Revised: 02/17/2011] [Accepted: 06/16/2011] [Indexed: 01/22/2023]
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Sildenafil and glyceryl trinitrate reduce tactile allodynia in streptozotocin-injected rats. Eur J Pharmacol 2010; 631:17-23. [DOI: 10.1016/j.ejphar.2010.01.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 12/08/2009] [Accepted: 01/06/2010] [Indexed: 11/18/2022]
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Huang J, Cai Q, Chen Y, Hong Y. Treatment with ketanserin produces opioid-mediated hypoalgesia in the late phase of carrageenan-induced inflammatory hyperalgesia in rats. Brain Res 2009; 1303:39-47. [PMID: 19782054 DOI: 10.1016/j.brainres.2009.09.072] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Revised: 09/16/2009] [Accepted: 09/17/2009] [Indexed: 11/26/2022]
Abstract
Both pro-nociceptive and antinociceptive mediators are released in the tissues during inflammation. Balance of these two types of mediators determines the induction and maintenance of pain or hypernociception. This study was designed to explore whether 5-HT(2A) receptors in the periphery contributed to the maintenance of carrageenan-evoked hyperalgesia. Intraplantar (i.pl.) injection of carrageenan evoked hyperalgesia detected by noxious heat stimulus. The 5-HT(2A) receptor antagonist ketanserin administered i.pl. 1 h after carrageenan dose-dependently (2-20 microg) prolonged paw withdrawal latency (PWL) during the late phase (24 h) of carrageenan-evoked inflammation. Following treatments with carrageenan and ketanserin, i.pl. injection of formalin (1%) produced significantly fewer nocifensive behaviors and expression of c-Fos protein in the spinal dorsal horn, confirming the hypoalgesic status in the inflamed site. However, injection of ketanserin in naive site failed to produce hypoalgesia. The hypoalgesia was completely abolished by local or systemic injection of naloxone methiodide. The present study suggests that 5-HT(2A) receptors were involved in the maintenance of inflammatory pain, and that 5-HT suppressed inflammation-associated endogenous opioid analgesia contributing to its pro-nociceptive actions in the periphery. It implied a possible therapeutic benefit of blockade of local 5-HT(2A) receptors in the treatment of inflammatory pain.
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Affiliation(s)
- Jian Huang
- Key Provincial Laboratory of Developmental and Neurological Biology, College of Life Sciences, Fujian Normal University, Fuzhou 350108, People's Republic of China
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Hervera A, Leánez S, Negrete R, Pol O. The peripheral administration of a nitric oxide donor potentiates the local antinociceptive effects of a DOR agonist during chronic inflammatory pain in mice. Naunyn Schmiedebergs Arch Pharmacol 2009; 380:345-52. [PMID: 19636536 DOI: 10.1007/s00210-009-0436-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Accepted: 07/07/2009] [Indexed: 12/01/2022]
Abstract
Several works reveal that nitric oxide could enhance the peripheral antinociception induced by opioids during acute inflammation. Nonetheless, the role of nitric oxide in the local antinociceptive effects of delta-opioid receptor (DOR) agonists during chronic peripheral inflammation is not known. The aim of this study is to evaluate whether nitric oxide would enhance the local antinociceptive effects of a DOR agonist during chronic inflammatory pain in mice. Chronic inflammatory pain was induced by the subplantar administration of complete Freund's adjuvant (CFA; 30 microl) and thermal hyperalgesia assessed by plantar test. In C57BL/6J mice, we evaluated the local antinociceptive effects of a DOR agonist, [D-Pen2,5]-enkephalin (DPDPE) and a nitric oxide donor, DETA NONOate DETA/NO 2,2'-(hydroxynitrosohydrazino) Bis-Ethanamine (NOC-18) alone or combined (DPDPE plus NOC-18) at 1, 4, 7, and 10 days after CFA injection. The reversibility of the peripheral antinociceptive effects of DPDPE, alone or combined with NOC-18, was assessed with the local administration of selective (naltrindole) and non-selective (naloxone methiodide) DOR antagonists. The local administration of DPDPE or NOC-18 alone dose-dependently inhibited the thermal hyperalgesia induced by peripheral inflammation. Moreover, the co-administration of NOC-18 with DPDPE significantly increased the antinociceptive effects produced by DPDPE from 1 to 10 days of CFA-induced inflammatory pain (P < 0.05). These effects were completely blocked by naltrindole and naloxone methiodide. Our results demonstrate that nitric oxide might enhance the local antinociceptive effects of a DOR agonist during chronic inflammatory pain by interaction with peripheral DOR, representing a useful strategy for an efficient antinociceptive treatment of peripheral inflammatory pain.
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MESH Headings
- Analgesics, Opioid/administration & dosage
- Animals
- Chronic Disease
- Disease Models, Animal
- Drug Therapy, Combination
- Enkephalin, D-Penicillamine (2,5)-/administration & dosage
- Freund's Adjuvant
- Hot Temperature
- Hyperalgesia/drug therapy
- Hyperalgesia/etiology
- Hyperalgesia/metabolism
- Inflammation/chemically induced
- Inflammation/drug therapy
- Inflammation/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Naltrexone/administration & dosage
- Naltrexone/analogs & derivatives
- Narcotic Antagonists/administration & dosage
- Nitric Oxide/metabolism
- Nitric Oxide Donors/administration & dosage
- Nitric Oxide Donors/metabolism
- Nitroso Compounds/administration & dosage
- Nitroso Compounds/metabolism
- Pain Measurement
- Receptors, Opioid, delta/agonists
- Receptors, Opioid, delta/metabolism
- Time Factors
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Affiliation(s)
- Arnau Hervera
- Grup de Neurofarmacologia Molecular, Institut de Recerca, Hospital de la Sta Creu i Sant Pau & Institut de Neurociències, Universitat Autònoma de Barcelona, Barcelona, Spain
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Leánez S, Hervera A, Pol O. Peripheral antinociceptive effects of µ- and δ-opioid receptor agonists in NOS2 and NOS1 knockout mice during chronic inflammatory pain. Eur J Pharmacol 2009; 602:41-9. [DOI: 10.1016/j.ejphar.2008.11.019] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Revised: 10/27/2008] [Accepted: 11/10/2008] [Indexed: 10/21/2022]
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Wang CL, Wang X, Yu Y, Cui Y, Liu HM, Lai LH, Guo C, Liu J, Wang R. Type 1 diabetes attenuates the modulatory effects of endomorphins on mouse colonic motility. Neuropeptides 2008; 42:69-77. [PMID: 18023865 DOI: 10.1016/j.npep.2007.10.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Revised: 10/07/2007] [Accepted: 10/07/2007] [Indexed: 12/13/2022]
Abstract
Our previous studies have shown that endomorphins (EMs), endogenous ligands for mu-opioid receptor, display a significant potentiation effect on mouse colonic motility. In the present study, to assess whether diabetes alters these modulatory effects of EMs on colonic motility, we investigated the effects of EMs in type 1 diabetic mouse colon in vitro. At 4 weeks after the onset of diabetes, carbachol-induced contractions in the longitudinal muscle of distal colon were significantly reduced compared to those of non-diabetic mice. Furthermore, the contractile effects induced by EMs in the longitudinal muscle of distal colon and in the circular muscle of proximal colon were also significantly reduced by type 1 diabetes. It is noteworthy that EMs-induced longitudinal muscle contractions were not significantly affected by atropine, Nomega-nitro-l-arginine methylester (l-NAME), phentolamine, propranolol, hexamethonium, methysergide and naltrindole. On the other hand, tetrodotoxin, indomethacin, naloxone, beta-funaltrexamine, naloxonazine and nor-binaltorphimine completely abolished these effects. These mechanisms responsible for EMs-induced modulatory effects in type 1 diabetes were in good agreement with those of non-diabetes, indicating similar mechanisms in both diabetes and non-diabetes. At 8 weeks after the onset of diabetes, both carbachol- and EMs-induced longitudinal muscle contractions were similar to those of short-time (4 weeks) diabetic mice. In summary, all the results indicated that type 1 diabetes significantly attenuated the modulatory effects of EMs on the mouse colonic motility, but the mechanisms responsible for these effects were not significantly altered.
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Affiliation(s)
- Chang-lin Wang
- State Key Laboratory of Chinese Medicine and Molecular Pharmacology, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China
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Yu Y, Wang X, Cui Y, Fan YZ, Liu J, Wang R. Abnormal modulation of cholinergic neurotransmission by endomorphin 1 and endomorphin 2 in isolated bronchus of type 1 diabetic rats. Peptides 2006; 27:2770-7. [PMID: 16901587 DOI: 10.1016/j.peptides.2006.06.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2006] [Revised: 06/05/2006] [Accepted: 06/12/2006] [Indexed: 10/24/2022]
Abstract
To assess whether diabetes alters the regulatory effects of mu-opioid receptor (MOR) agonists on the cholinergic bronchoconstriction, we investigated the inhibitory effects of endomorphins (EMs) on the electrical field stimulation (EFS)-induced cholinergic bronchoconstriction in type 1 diabetic rats. At 4 weeks after the onset of diabetes, both the EFS- and exogenous acetylcholine (ACh)-induced bronchoconstriction in diabetes in vitro were greater than those in non-diabetes rats. Furthermore, endomorphin 1 (EM1) and endomorphin 2 (EM2) inhibited the response to EFS in diabetic rat isolated bronchus in a concentration- and frequency-dependent manner, which is in agreement with that in non-diabetes. However, the inhibitory effects of EMs on the EFS-induced bronchoconstriction in diabetes were significantly weaker than those in non-diabetes. Both EM1 and EM2 (1 microM) had no effect on the contractile response to exogenous ACh, indicating a prejunctional effect. Furthermore, the inhibitory effect on the EFS-induced bronchoconstriction was blocked by naloxone (10 microM). Eight weeks after the induction of diabetes, both the EFS- and exogenous ACh-induced bronchoconstrictions in diabetes were further enhanced compared to those in short-time (4 weeks) diabetic rats. Moreover, the inhibitory effects of EMs on the EFS-induced bronchoconstriction were further attenuated. These results suggest that dysfunction of presynaptic inhibitory modulation through opioid receptor by EMs may take place in the bronchus of diabetic rats.
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Affiliation(s)
- Ye Yu
- Department of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, 222 Tian Shui South Road, Lanzhou 730000, PR China
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Abstract
This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, USA.
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Pol O, Sasaki M, Jiménez N, Dawson VL, Dawson TM, Puig MM. The involvement of nitric oxide in the enhanced expression of mu-opioid receptors during intestinal inflammation in mice. Br J Pharmacol 2005; 145:758-66. [PMID: 15852037 PMCID: PMC1576189 DOI: 10.1038/sj.bjp.0706227] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Intestinal inflammation enhances the potency of mu-opioid receptor (MOR) agonists inhibiting gastrointestinal transit and increases the expression of MOR in mice intestine. The precise mechanisms implicated in the increased expression of MOR during intestinal inflammation are not known. The aim of the study is to evaluate if nitric oxide released during intestinal inflammation could modulate MOR gene expression and affect gastrointestinal transit. Intestinal inflammation was induced by the intragastric administration of croton oil. In CD-1 mice, with and without inflammation, we evaluated the anti-transit effects of morphine in animals treated with NOS inhibitors (L-NAME and L-NIL) and the intestinal levels of iNOS enzyme mRNA. The anti-transit effects of morphine and the expression of MOR mRNA in the gut of wild-type (WT) and iNOS-/- mice were also assessed. Gastrointestinal transit was measured with charcoal meal and mRNA levels determined by real-time PCR. In CD-1 mice, inflammation induced a 10-fold increase (P<0.0001) in iNOS mRNA levels in the gut. The absence of iNOS gene and treatment of CD-1 mice with L-NAME or L-NIL abolished the increased antitransit effects of morphine observed during inflammation. Moreover, although the basal levels of MOR mRNA were similar in WT and iNOS animals (-/-), intestinal inflammation only increased the MOR expression in the gut of WT (P<0.01) but not in iNOS-/- mice. The results suggest that nitric oxide derived from the increased expression of iNOS is implicated in the enhanced effects of morphine and in the upregulation of MOR gene transcription observed during intestinal inflammation.
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Affiliation(s)
- Olga Pol
- Anesthesiology Research Unit, Institut Municipal d'Investigació Mèdica, Universitat Autònoma de Barcelona, Hospital del Mar, Doctor Aiguader 80, Barcelona 08003, Spain.
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Jiménez N, Puig MM, Pol O. Antiexudative Effects of Opioids and Expression of κ- and δ- Opioid Receptors during Intestinal Inflammation in Mice: Involvement of Nitric Oxide. J Pharmacol Exp Ther 2005; 316:261-70. [PMID: 16183704 DOI: 10.1124/jpet.105.091991] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The study evaluates the effects of kappa- (KOR), delta- (DOR), and mu-opioid receptor (MOR) agonists on the inhibition of plasma extravasation during acute and chronic intestinal inflammation in mice. The antiexudative effects of KOR and DOR agonists in animals treated with nitric oxide synthase (NOS) inhibitors and their protein levels in the gut (whole jejunum and mucosa) and spinal cord of mice with chronic intestinal inflammation were also measured. Inflammation was induced by the intragastric administration of one (acute) or two (chronic) doses of croton oil. Plasma extravasation was measured using Evans blue and protein levels by Western blot and immunoprecipitation. Plasma extravasation was significantly increased 2.7 times during chronic inflammation. The potency of the KOR agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolydinyl)cyclohexyl]-benzeneazetamine (U50,488H) inhibiting plasma extravasation was enhanced 26.3 times during chronic compared with acute inflammation. [d-Pen(2),d-Pen(5)]-Enkephalin (DPDPE) (a DOR agonist) was also 11.8 times more potent during chronic inflammation, whereas the antiexudative effects of fentanyl (a MOR agonist) were not significantly altered. Receptor-specific antagonists reversed the effects. Protein levels of KOR and DOR in the whole jejunum and mucosa were significantly increased after chronic inflammation. Treatment with NOS inhibitors N(omega)-nitro-l-arginine methyl ester or l-N(6)-(1-iminoethyl)-lysine hydrochloride diminished plasma extravasation and inhibited the increased antiexudative effects of U50,488H and DPDPE during chronic intestinal inflammation. The data show that the enhanced antiexudative effects of KOR and DOR agonists could be related to an increased expression of KOR and DOR in the gut and that the release of nitric oxide may play a role augmenting the effects of opioids during chronic inflammation.
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Affiliation(s)
- Natalia Jiménez
- Laboratori de Neurofarmacologia Molecular, Institut de Recerca, Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, Edifici C-Z, 08193 Barcelona, Spain
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Liu J, Yu Y, Fan YZ, Chang H, Liu HM, Cui Y, Chen Q, Wang R. Cardiovascular effects of endomorphins in alloxan-induced diabetic rats. Peptides 2005; 26:607-14. [PMID: 15752575 DOI: 10.1016/j.peptides.2004.11.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2004] [Revised: 11/21/2004] [Accepted: 11/23/2004] [Indexed: 10/26/2022]
Abstract
Endomorphins, the endogenous, potent and selective mu-opioid receptor agonists, have been shown to decrease systemic arterial pressure (SAP) in rats. In the present study, responses to endomorphins were investigated in systemic vascular bed of alloxan-induced diabetic rats and in non-diabetic rats. Diabetes was induced by alloxan (220 mg/kg, i.p.) in male Wistar rats. At 4-5 weeks after the onset of diabetes, intravenous injections of endomorphins (1-30 nmol/kg) led to an increase of SAP and heart rate (HR) consistently and dosed-dependently. SAP increased 7.68+/-3.73, 11.19+/-4.55, 21.19+/-2.94 and 27.48+/-6.21% from the baseline at the 1, 3, 10 and 30 nmol/kg dose, respectively, of endomorphin 1 (n=4; p<0.05), and similar changes were observed in response to endomorphin 2. The hypertension could be antagonized markedly by i.p. 2 mg/kg of naloxone. On the other hand, bilateral vagotomy would attenuate the effects of hypertension and diminished the changes of HR in response to endomorphins. With diabetic rats, 6-10 weeks after the induction of diabetes, intravenous injections of endomorphins produced non-dose-related various changes in SAP, such as a single decrease, or a single increase, or biphasic changes characterized by an initial decrease followed by a secondary increase, or no change at all. These results suggest that diabetes may lead to the dysfunction of the cardiovascular system in response to endomorphins. Furthermore, the diabetic rats of 4-5 weeks after alloxan-treatment, the increase in SAP and HR caused by i.v. endomorphins might be explained by a changed effect of vagus and by a naloxone-sensitive mechanism.
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Affiliation(s)
- Jing Liu
- Department of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, 222 Tian Shui South Road, Lanzhou 730000, PR China
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