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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pain induced by a stimulus that is normally not painful is referred to as hyperalgesic pain. Inhibition of arachidonic acid metabolism and/or sympathectomy have been found to be effective treatment for this type of pain. We propose that the lowered pain threshold is induced by arachidonic acid metabolites produced in inflamed tissue or by sympathetic postganglionic neurons after nerve injury. The most extensively studied hyperalgesic mediators are prostaglandin E(2) (PGE(2)) and prostacyclin (PGI(2)), products of the cyclooxygenase pathway of arachidonic acid metabolism, whose production is inhibited by nonsteroidal antiinflammatory analgesics (NSAIAs). Recent studies, however, have demonstrated that products of the NSAIA-resistant lipoxygenase pathway of arachidonic acid metabolism are also hyperalgesic. Their production is inhibited by corticosteroids and current experimental agents.
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PMID:Hyperalgesic pain: a review. 196 69

Platelet activation, with subsequent formation of thromboxane A2 (TxA2), is thought to play a role in the development of arterial occlusion. In patients with severe atherosclerosis of the lower limbs, characterized by leg ulcers and rest pain, the basal formation of TxA2 and prostacyclin (PGI2) is increased. Corresponding data in patients with more moderate atherosclerosis of the lower limbs have not been reported. Since the capacity to physical exercise is not blunted in such patients proper evaluation of their TxA2-PGI2 synthesis should comprise not only assessment of the basal formation, but also TxA2/PGI2 biosynthesis during conditions of elevated cardiovascular activity. To address this, we analysed these eicosanoids in patients with a history of intermittent claudication. Urinary dinor-metabolites of TxB2 and PGI2 (Tx-M and PGI-M, respectively) were estimated by gas chromatography/negative ion-chemical ionization mass spectrometry in samples collected prior to, during and immediately after 20 min of severe treadmill exertion. The basal excretion of Tx-M was 105 +/- 26 pg/mg creatinine. It was not changed during exercise, but increased to 176 +/- 48 pg/mg creatinine (P less than 0.05) during the recovery. The basal excretion of PGI-M was 142 +/- 25 pg/mg creatinine. The PGI-M response to exercise varied from no change at all to a 30-fold increase, without any obvious correlation to experienced leg pain, walking distance or other recorded variables. During the recovery period the outflow of PGI-M was significantly higher than at rest (482 +/- 145 pg/mg creatinine; P less than 0.01). We conclude that in patients with intermittent claudication due to atherosclerosis (1) platelet activation does not occur during the course of the exercise, and (2) vascular prostacyclin formation can be dissociated from of TxA2 synthesis. The observed increase in PGI-M in some of the patients is suggested to reflect tissue ischaemia induced by the lack of adequate hyperaemia during exercise.
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PMID:Excretion of thromboxane A2 and prostacyclin metabolites during treadmill exercise in patients with intermittent claudication. 340 85

The spinal cord is one of the sites where non-steroidal anti-inflammatory drugs (NSAIDs) act to produce analgesia and antinociception. Expression of cyclooxygenase(COX)-1 and COX-2 in the spinal cord and primary afferents suggests that NSAIDs act here by inhibiting the synthesis of prostaglandins (PGs). Basal release of PGD(2), PGE(2), PGF(2alpha) and PGI(2) occurs in the spinal cord and dorsal root ganglia. Prostaglandins then bind to G-protein-coupled receptors located in intrinsic spinal neurons (receptor types DP and EP2) and primary afferent neurons (EP1, EP3, EP4 and IP). Acute and chronic peripheral inflammation, interleukins and spinal cord injury increase the expression of COX-2 and release of PGE(2) and PGI(2). By activating the cAMP and protein kinase A pathway, PGs enhance tetrodotoxin-resistant sodium currents, inhibit voltage-dependent potassium currents and increase voltage-dependent calcium inflow in nociceptive afferents. This decreases firing threshold, increases firing rate and induces release of excitatory amino acids, substance P, calcitonin gene-related peptide (CGRP) and nitric oxide. Conversely, glutamate, substance P and CGRP increase PG release. Prostaglandins also facilitate membrane currents and release of substance P and CGRP induced by low pH, bradykinin and capsaicin. All this should enhance elicitation and synaptic transfer of pain signals in the spinal cord. Direct administration of PGs to the spinal cord causes hyperalgesia and allodynia, and some studies have shown an association between induction of COX-2, increased PG release and enhanced nociception. NSAIDs diminish both basal and enhanced PG release in the spinal cord. Correspondingly, spinal application of NSAIDs generally diminishes neuronal and behavioral responses to acute nociceptive stimulation, and always attenuates behavioral responses to persistent nociception. Spinal application of specific COX-2 inhibitors sometimes diminishes behavioral responses to persistent nociception.
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PMID:Prostaglandins and cyclooxygenases [correction of cycloxygenases] in the spinal cord. 1127 57

Prostanoids sensitize sensory afferents during inflammation. However, their role in neuropathic pain is still unclear. We analyzed the actions of prostanoids, non-selective (indomethacin) or selective (celecoxib and NS-398) cyclooxygenase-2 (COX or COX-2) inhibitors, on the ectopic activity of dorsal root ganglia (DRG) and dorsal horn (DH) neurons in a model of neuropathic injury. Extracellular recordings of DRG and DH neurons and cardiovascular measurements were performed on anesthetized, paralyzed and artificially ventilated adult male Sprague-Dawley rats whose sciatic nerve had been transected. PGD(2), PGE(2), PGF(2alpha), carbaprostacyclin (cPGI(2); a stable prostacyclin analog), and carbocyclic thromboxane (cTXA(2)) were administered at cumulative doses (0.0001-5 mg/kg, i.p.) at 5 or 10 min intervals. Only cPGI(2) significantly increased the DRG and DH activity in a dose-dependent manner, with ED(50) values of 0.05 (0.01-0.96) and 0.69 (0.11-1.04) mg/kg, respectively. The other prostanoids did not significantly increase activity, although they reduced heart rate for up to 5 min following administration. Time course experiments with single doses of cPGI(2) (1 mg/kg, i.v.) increased DH discharge rate 3-17 min after injection. Indomethacin (3 mg/kg, s.c.), but not celecoxib or NS-398 (both at 6 mg/kg, s.c.), reduced both DRG and DH activity. Our results indicate that cPGI(2) excites DRG and DH neurons of neuropathic rats, and may suggest a role for IP prostanoid receptors in pain episodes associated with nerve injury. The inhibitory effect of indomethacin, but not celecoxib or NS-398, on ectopic activity may suggest that a tonic generation of PGI(2) by COX-1 could contribute to neuropathic pain.
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PMID:A stable prostacyclin analog enhances ectopic activity in rat sensory neurons following neuropathic injury. 1151 14

Despite the crucial role that prostaglandins (PGs) have in the sensitization of the central nervous system to pain, their cellular and molecular targets leading to increased pain perception have remained elusive. Here we investigated the effects of PGE(2) on fast synaptic transmission onto neurons in the rat spinal cord dorsal horn, the first site of synaptic integration in the pain pathway. We identified the inhibitory (strychnine-sensitive) glycine receptor as a specific target of PGE(2). PGE(2), but not PGF(2 alpha), PGD(2) or PGI(2), reduced inhibitory glycinergic synaptic transmission in low nanomolar concentrations, whereas GABAA, AMPA and NMDA receptor-mediated transmission remained unaffected. Inhibition of glycine receptors occurred via a postsynaptic mechanism involving the activation of EP2 receptors, cholera-toxin-sensitive G-proteins and cAMP-dependent protein kinase. Via this mechanism, PGE(2) may facilitate the transmission of nociceptive input through the spinal cord dorsal horn to higher brain areas where pain becomes conscious.
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PMID:PGE(2) selectively blocks inhibitory glycinergic neurotransmission onto rat superficial dorsal horn neurons. 1174 May 1

Existing therapies for major depressive disorder (MDD) have either limited efficacy and/or poor tolerability. The present study examined the effects of duloxetine, a potent and balanced dual reuptake inhibitor of serotonin (5-HT) and norepinephrine (NE), in patients with MDD. Adult patients (N = 267) with MDD were randomly assigned to receive duloxetine (60 mg/day) or placebo in this 9-week, multi-center, double-blind, parallel-group clinical trial. Efficacy was evaluated using the 17-item Hamilton Depression Rating Scale (HAMD(17)), Visual Analog Scales (VAS) for pain, Clinical Global Impression of Severity (CGI-S), Patient's Global Impression of Improvement (PGI-I), and Quality of Life in Depression Scale (QLDS). Safety was evaluated by assessing discontinuation rates, adverse event rates, vital signs, and laboratory tests. Duloxetine (60 mg QD) significantly reduced the HAMD(17) total score compared with placebo at the end of 9-week therapy. Estimated probabilities of response and remission were 65 and 43%, respectively, for duloxetine compared with 42 and 28% for placebo. Duloxetine also reduced overall pain, back pain, shoulder pain and time in pain while awake significantly more than placebo. Global measures of improvement, including PGI-I and QLDS, were significantly improved by duloxetine compared with placebo. Discontinuations due to adverse events were more frequent for duloxetine-treated patients (12.5%) than for placebo-treated patients (4.3%). Nausea, dry mouth, dizziness, and constipation were more frequent for duloxetine than placebo. There was no significant incidence of hypertension, nor any other safety issues. Duloxetine 60 mg administered once daily appears to be a safe and effective treatment for MDD.
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PMID:Duloxetine 60 mg once daily dosing versus placebo in the acute treatment of major depression. 1239 7

Here, we investigated the mechanism of the antihyperalgesic effect of capsaicin cream in the nerve injury-induced neuropathic pain model in mice. In naive mice, application of capsaicin cream onto footpad caused no significant changes in the thermal latency in contrast to the severe thermal hyperalgesia induced by a capsaicin ointment. On the other hand, application of the cream 3 h before test concentration dependently reversed both thermal and mechanical hyperalgesia observed after partial sciatic nerve injury in mice. In algogenic-induced nociceptive flexion (ANF) test, application of 0.1% capsaicin cream in naive mice blocked intraplantar (i.pl.) nociceptin- and ATP-induced flexion responses, whereas prostaglandin I(2) (PGI(2)) agonist-induced responses were unaffected. After nerve injury PGI(2) agonist-induced flexion responses were hypersensitized, and capsaicin cream concentration dependently blocked these hyperalgesic responses. Intraplantar injection of capsaicin solution in ANF test also produced potent flexion responses in naive mice that were lost after neonatal capsaicin-treatment. Partial sciatic nerve injury in neonatal capsaicin-treated mice caused reappearance of i.pl. capsaicin-induced flexion responses, suggesting novel expression of capsaicin receptors due to injury. The PGI(2) agonist-induced responses were also hypersensitized in such injured mice. Capsaicin cream completely reversed both i.pl. capsaicin- or i.pl. PGI(2) agonist-induced hyperalgesia in neonatal capsaicin-treated injured mice. Finally, novel expression of VR1 receptors on neonatal capsaicin-insensitive neurons after nerve injury was confirmed by immunohistochemistry. The newly expressed VR1 receptors after nerve injury were mainly confined to A-fibers. Together, our results suggest that novel expression of capsaicin receptors in neuropathic condition contributes to the analgesic effects of the capsaicin cream.
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PMID:Novel expression of vanilloid receptor 1 on capsaicin-insensitive fibers accounts for the analgesic effect of capsaicin cream in neuropathic pain. 1260 68

Sympathetic postganglionic neurons may be involved in the generation of pain, hyperalgesia and neurogenic inflammation under pathophysiological conditions. Experiments on animal models show that two categories of influence of the sympathetic neuron on afferent neurons can be distinguished and this distinction seems to be related as to whether sympathetic-afferent coupling develops after nerve lesion or after tissue trauma with inflammation. (1) Peripheral nerve lesion generates plastic changes of the afferent and sympathetic postganglionic neurons. This may lead to chemical coupling between sympathetic and afferent neurons which may entail activation and/or sensitization of primary afferent neurons by the sympathetic neurons. The mediator is probably noradrenaline and the afferent neuron expresses or upregulates functional adrenoceptors. The coupling may occur at different sites of the primary afferent neuron, e. g., at the lesion site, remote from the lesion site in the dorsal root ganglion or between nonlesioned sympathetic and afferent neurons which show collateral sprouting. The biochemical signals which trigger these changes probably are neurotrophic substances and their receptors which are synthesized by the peripheral neurons, Schwann cells and other cells in response to the peripheral lesions. (2) Sympathetic nerve terminals in peripheral tissues may serve as mediator elements in hyperalgesia and during inflammation following tissue trauma without nerve lesion. This function is largely independent of activity in the sympathetic neurons and independent of vesicular release of transmitter substances. The signals are probably synthesized and released from the sympathetic terminal or in association with it and belong to the prostaglandins (probably PGE(2) or PGI(2)). Furthermore, nerve growth factor (NGF) has a hyperalgesic action in inflammation which is at least in part dependent on the sympathetic nervous system.
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PMID:[Sympathetic nervous system and pain: pathophysiological mechanisms]. 1279 66

Searches for chemical mediators of inflammation underlying classical signs of inflammation i.e. heat, redness, swelling, and pain have been performed and various experimental models for evaluation of new agents to manage these inflammatory signs have been developed extensively during the last century. Now, at the beginning of the 21st-century, after great progress in gene technology, the necessity of in vivo animal study is being reconsidered. Therefore, this review introduces and describes findings obtained by the use of various experimental animal models. We have compared the inflammatory characteristics among species using reported animal models such as dye exudation in the skin, paw edema, pleurisy, and writhing reaction; then we have precisely examined mediators involved in these inflammatory reactions. In the process of plasma exudation and pain perception in the earlier phases of acute inflammation, involvement of the kallikrein-kinin system and prostanoids was demonstrated. Precisely, bradykinin, and PGI(2) among the prostanoids, are major mediators for exudation and pain perception of the initial acute phase of inflammation; both mediators collaborate to enhance these effects. PGE(2), perhaps produced by cyclooxygenase-2, was involved in induction of plasma exudation and pain perception in a later phase than the timing of involvement of PGI(2). Precise roles of various prostanoids will hopefully be clarified by the research projects in progress.
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PMID:Critical roles for bradykinin and prostanoids in acute inflammatory reactions: a search using experimental animal models. 1456 Nov 83

A group of chemical mediators, the eicosanoids, is critical players in a multitude of physiological processes. Generated by the action of the cyclooxygenase (COX) enzyme on arachidonic acid they are responsible for diverse and often opposing actions such as platelet function, vasomotor tone, gastric cytoprotection and inflammation. Since their discovery several decades ago, our knowledge concerning their synthesis, function as natural ligands and methods to manipulate their activity through drug development has expanded. Traditional Non Steroidal Anti-Inflammatory Drugs (NSAIDs) are nonselective inhibitors of the COX enzyme, of which two isoforms are known to exist - COX-1 and COX-2. NSAIDs have been the mainstay of treatment in the management of pain and inflammation associated with acute and chronic inflammatory conditions that affect more than 10 million Americans. Their efficacy in this regard is not questioned. However, gastrointestinal toxicity arising from chronic NSAID ingestion is common and limits their use in clinical practice. Gastrointestinal toxicity has been attributed to the blockade of the COX-1 mediated generation of the cytoprotective prostanoids, such as PGE(2) and PGI(2). Selective COX-2 inhibitors were designed to inhibit the production of COX-2 dependent inflammatory prostanoids and to leave intact the cytoprotective COX-1 products. The first of a new class of these selective COX-2 inhibitors - the coxibs- were introduced to the market in 1999. These compounds, while exhibiting similar efficacy to traditional NSAIDs, were associated with a reduced incidence of surrogate or actual indices of GI toxicity. Questions have been raised concerning the cardiovascular and renal profiles of these agents based on data from both small and large clinical studies. More recently, our increasing understanding of the relative contributions of both isoforms of the COX enzyme to individual components of vascular homeostais has allowed us to appreciate the cardiovascular and renovascular implications of selective COX-2 inhibition.
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PMID:Cardiovascular and renovascular implications of COX-2 inhibition. 1496 23


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