Prostaglandins as modulators of pain

Cerebrospinal Fluid Profile of Lipid Mediators in Alzheimer's Disease

Alzheimer's disease (AD) develops into dementia over a period of several years, during which subjective cognitive impairment (SCI) and mild cognitive impairment (MCI) can be used as intermediary diagnoses of increasing severity. Chronic neuroinflammation resulting from insufficient resolution is involved in the pathogenesis of AD and is associated with cognitive impairment. Specialized pro-resolving lipid mediators (LMs) that promote the resolution of inflammation may be valuable markers in AD diagnosis and as therapeutic targets. Liquid chromatography-tandem mass spectrometry was used to analyze pro-resolving and pro-inflammatory LMs in cerebrospinal fluid (CSF) from patients with cognitive impairment ranging from subjective impairment to a diagnosis of AD and correlated to cognition, CSF tau, and β-amyloid. Resolvin (Rv) D4, RvD1, neuroprotectin D1 (NPD1), maresin 1 (MaR1), and RvE4 were lower in AD and/or MCI compared to SCI. The pro-inflammatory LTB₄ and 15-HETE were higher in AD and MCI, respectively, while PGD2, PGE2, and PGF2a were decreased in AD, compared to SCI. RvD4 was also negatively correlated to AD tangle biomarkers, and positive correlations to cognitive test scores were observed for both pro-resolving LMs and their precursor fatty acids. In this exploratory study of the lipidome in CSF of AD, MCI, and SCI, the results indicate a shift in the LM profile from pro-resolving to pro-inflammatory in progression to AD, suggesting that it may be of use as a biomarker when followed by confirmation by replication studies.

A dose response study of the effect of prostaglandin E2 on thermal nociceptive sensitivity

Inhibition of prostaglandin (PG) biosynthesis has been used to relieve pain for thousands of years. Today non-steroidal anti-inflammatory drugs (which largely inhibit PG synthesis) are widely used to treat pain. Four main types of PGs (PGD2, PGE2, PGF2 and PGI2) are synthesized from arachidonic acid during inflammation and have been demonstrated to impact nociception. PGE2 has been the most studied and utilized for its pain producing properties and has been demonstrated to increase hypersensitivity in rodent nociceptive behavioral models when applied centrally and/or peripherally. Surprisingly, there are no published reports that use withdrawal from radiant light beam (Hargreaves apparatus) to examine the dose response effect of peripherally applied PGE2 on thermal nociceptive hypersensitivity. To address this gap in the literature, we performed a dose response study examining the effect of PGE2 on thermal hypersensitivity (assessed using a Hargreaves apparatus) where rats were injected with 0.003-30μg of PGE2, intradermally into the hindpaw. Thermal hypersensitivity was assessed by measuring withdraw latency from a radiant light beam (Hargreaves test) and our primary objective was to determine the dose of PGE2 causing the most pronounced increase in thermal hypersensitivity (i.e. lowest withdraw latency). A secondary objective was to determine the minimum dose of PGE2 required to cause statistically significant decreases in thermal withdrawal latency as compared to rats injected with vehicle. We found that rats injected with the 30μg dose of PGE2 exhibited the most pronounced thermal nociceptive hypersensitivity though secondary analysis showed that rats injected with PGE2 doses of 0.03-30μg had lower withdrawal latencies as compared to rats injected with vehicle. This work fills an evidence gap and provides context to guide dose selection in future rodent pain behavior studies.

Postoperative pain management

Postoperative pain is a very important issue for several patients. Indifferent of the surgery type or method, pain management is very necessary. The relief from suffering leads to early mobilization, less hospital stay, reduced hospital costs, and increased patient satisfaction. An individual approach should be applied for pain control, rather than a fix dose or drugs. Additionally, medical, psychological, and physical condition, age, level of fear or anxiety, surgical procedure, personal preference, and response to agents given should be taken into account. The major goal in the management of postoperative pain is minimizing the dose of medications to lessen side effects while still providing adequate analgesia. Again a multidisciplinary team approach should be pursued planning and formulating a plan for pain relief, particularly in complicated patients, such as those who have medical comorbidities. These patients might appear increase for analgesia-related complications or side effects.

Expression of leukotriene receptors in the rat dorsal root ganglion and the effects on pain behaviors

Background

Leukotrienes (LTs) belong to the large family of lipid mediators implicated in various inflammatory conditions such as asthma and rheumatoid arthritis. Four distinct types (BLT1, BLT2, CysLT1 and CysLT2) of G-protein-coupled receptors for LTs have been identified. Several studies have reported that LTs are involved in inflammatory pain, but the mechanism and the expression of LT receptors in the nociceptive pathway are unknown.

Results

We investigated the precise expression of these four types of LT receptors in the adult rat dorsal root ganglion (DRG) using reverse transcription-polymerase reaction (RT-PCR) and radioisotope-labeled in situ hybridization histochemistry (ISHH). We detected mRNAs for BLT1 and CysLT2 in the DRG, but not for BLT2 and CysLT1. CysLT2 mRNA was preferentially expressed by small sized DRG neurons (about 36% of total neurons), whereas BLT1 mRNA was expressed by non-neuronal cells. Double labeling analysis of CysLT2 with NF-200, calcitonin gene-related peptide (CGRP), isolectin B4 (IB4), transient receptor potential vanilloid subfamily 1 (TRPV1) and P2X3 receptor revealed that many CysLT2-labeled neurons were localized with unmyelinated and non-peptidergic neurons, and interestingly, CysLT2 mRNA heavily co-localized with TRPV1 and P2X3-positive neurons. Intraplantar injection of LTC4, a CysLT2 receptor agonist, itself did not induce the thermal hyperalgesia, spontaneous pain behaviors or swelling of hind paw. However, pretreatment of LTC4 remarkably enhanced the painful behaviors produced by alpha, beta-methylene adenosine 5'-triphosphate (αβ-me-ATP), a P2X3 receptor agonist.

Conclusions

These data suggests that CysLT2 expressed in DRG neurons may play a role as a modulator of P2X3, and contribute to a potentiation of the neuronal activity following peripheral inflammation.

Effect of mineral trioxide aggregate on rat clonal dental pulp cells: expression of cyclooxygenase-2 mRNA and inflammation-related protein via nuclear factor kappa B signaling system

INTRODUCTION

Recently, mineral trioxide aggregate (MTA) has been routinely used for endodontic treatment. It is well-known that MTA induced secondary dentin formation in pulp cavity when it was applied to dentin, whereas its cytotoxicities were unclear. The purpose of this study was to evaluate the effect of MTA on rat clonal dental pulp cells, RPC-C2A.

METHODS

This study was conducted to observe the response of RPC-C2A cells on MTA with reverse-transcriptase polymerase chain reaction, Western blot analysis, and enzyme immunoassay. Data were compared by analysis of variance. Statistical significance was established at P <.01.

RESULTS

MTA significantly caused an up-regulation of cyclooxygenase-2 (COX-2) and inducible form of nitric oxide synthase (iNOS) mRNA expression. Furthermore, MTA caused inhibitory kappa B (IkappaB) phosphorylation and translocation of nuclear factor-kappa B (NF-kappaB) subunits to nucleus. Curucumin, an inhibitor of NF-kappaB activation, suppressed MTA-induced COX-2 and iNOS mRNA expressions. In addition, MTA increased the production of prostaglandin E(2) in comparison with the controls.

CONCLUSIONS

MTA induces inflammation via NF-kappaB signaling system.

Prostaglandin E2 production and viability of cells cultured in contact with freshly mixed endodontic materials

AIM

To determine whether commonly used endodontic sealers could either induce or increase the release of prostaglandin E2 (PGE2) when in contact with cell types found in the periapical tissues.

METHODOLOGY

Freshly mixed samples of Roth 801 sealer, Sealapex and ProRoot mineral trioxide aggregate (MTA) were placed in contact with cultured macrophages and fibroblasts for 24 h. The supernatant from the cultures was assayed for PGE2 using enzyme-linked immunosorbent assay. Cell viability counts were made. As a positive control, similar cultures were also exposed to lipopolysaccharide and the supernatant analysed for PGE2. Data were compared by anova.

RESULTS

The three materials examined in these experiments did not stimulate increased PGE2 release from either of the cell lines. In control cultures, lipopolysaccharide increased PGE2 release from macrophages but not from fibroblasts. Viability counts revealed that, whilst Roth 801 sealer caused some cell death in both fibroblasts and macrophages, Sealapex led to cell death only in the macrophage cultures. ProRoot MTA did not lead to statistically significant cell death in either culture.

CONCLUSIONS

Under 24-h culture conditions, the three freshly mixed test materials did not increase directly either production or release of PGE2 from either macrophages or gingival fibroblasts. Roth 801 decreased cell viability counts for both fibroblasts and macrophages. Sealapex decreases macrophage viability. ProRoot MTA did not affect viability in either cell line.

Changes in blood glucose and plasma insulin levels induced by bradykinin in anaesthetized rats

1. The influence of bradykinin (BK) on blood glucose and plasma insulin levels was investigated in anaesthetized rats. 2. Blood glucose level was dose-dependently increased by intravenous infusion of BK. This effect of BK was enhanced by captopril, an inhibitor of angiotensin-converting enzyme (ACE). Des-Arg9-bradykinin (DABK), a kinin B1 receptor agonist, did not modify blood glucose levels while the effect of BK was inhibited by Hoe-140, a kinin B2 receptor antagonist. 3. The effect of BK was reduced by the NO-synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), and by the cyclo-oxygenase inhibitor, indomethacin. The effect of BK was suppressed by the association of propranolol with phentolamine or phenoxybenzamine. It was also reduced by hexamethonium, a ganglion-blocking drug. In adrenalectomized rats, the infusion of BK slightly decreased blood glucose levels. 4. The hyperglycaemic effect of adrenaline was suppressed by propranolol associated with phentolamine or phenoxybenzamine, but it was not modified by L-NAME. 5. Infusion of BK did not modify plasma insulin levels. However, after phentolamine and propranolol, BK induced a transient 2 fold rise in plasma insulin levels. The release of insulin was dose-dependent and inhibited by Hoe-140. 6. We conclude that infusion of BK induces, via a stimulation of B2 receptors, the release of NO and of prostanoids. The latter agents activate through a reflex pathway the release of catecholamines from the adrenal medulla. This release increases blood glucose levels and reduces plasma insulin levels. After adrenoceptor inhibition, BK induces a secretion of insulin, via the stimulation of B2 receptors.

Analgesic efficacy and safety of nonpreserved ketorolac tromethamine ophthalmic solution following radial keratotomy. Ketorolac Radial Keratotomy Study Group

PURPOSE

To compare the analgesic efficacy and safety of nonpreserved ketorolac tromethamine 0.5% with those of its vehicle in the treatment of postsurgical ocular pain following radial keratotomy.

METHODS

This study employed a multicenter, double-masked, randomized, parallel-group design. Radial keratotomy patients were treated with either nonpreserved ketorolac tromethamine 0.5% or its vehicle four times daily for up to 3 days following surgery. Patients were provided with an escape medication (acetaminophen) for use only as needed for intolerable pain.

RESULTS

Patients treated with ketorolac reported significantly greater pain relief (P < or =.023), less pain intensity (P < or =.047), less use of escape medication (P < or =.001), fewer symptoms of ocular discomfort (P=.024), and fewer sleep disturbances (P < or =.013) than did patients treated with vehicle. No treatment-related adverse events were reported in the ketorolac group, and only one treatment-related adverse event was reported in the vehicle group. Most other safety findings were equivalent in the two treatment groups except that there were significantly less eyelid erythema (P=.026) and eyelid edema (P < or =.001) in the ketorolac group.

CONCLUSIONS

Nonpreserved ketorolac tromethamine 0.5% ophthalmic solution was significantly more effective than, and as safe as, vehicle in the treatment of postoperative pain associated with radial keratotomy. Therefore, topical ketorolac may be a valuable treatment option for the maintenance of patient comfort following refractive surgery.

Effects of the non-peptide B2 antagonist FR173657 on kinin-induced smooth muscle contraction and relaxation, vasoconstriction and prostaglandin release

1. The non-peptide bradykinin (BK) antagonist (E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinolin yl) oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide (FR173657) was tested in intestinal, uterine, tracheal and vascular in vitro preparations. The investigation aimed at determining the antagonistic potency, duration of action, specificity for BK receptors and apparent mode of antagonistic action of FR173657. 2. Contractions of the isolated ileum of the guinea-pig in response to BK were inhibited by FR173657 (10-300 nM) in a concentration-dependent manner. The inhibition lasted for up to 90 min after wash-out of FR173657. Cumulative concentration-response curves to BK were shifted to the right with a concomitant decrease in the maximum effect. A pKB value of 8.7 was determined. FR173657 had no effect on contractions induced by acetylcholine, histamine, 5-hydroxytryptamine, substance P, angiotensin II or caerulein. 3. The concentration-response curves for B2 receptor-mediated relaxations of the rat isolated duodenum induced by BK were shifted to the right together with a concomitant reduction of the maximum BK effect in the presence of FR173657 (10-300 nM). A pKB of 9.0 +/- 0.2 was calculated. FR173657 had no effect on B1 receptor-mediated relaxations in response to des-Arg9-BK. 4. The concentration-response curves for BK-induced contractions of the rat isolated uterus were shifted to the right by FR173657 (3-300 nM) in a concentration-dependent and parallel manner. The Schild plot for the inhibition caused by FR173657 had a slope of -0.98 indicating a competitive mode of antagonism. A pA2 value of 9.1 was determined. 5. Contractions of the circular smooth muscles of the guinea-pig isolated trachea in response to BK were concentration-dependently inhibited by FR173657 (10-100 nM). An affinity estimate of 9.3 was calculated for FR173657. Contractions induced by acetylcholine and relaxations in response to isoprenaline remained completely unaffected by FR173657. 6. In the rabbit isolated perfused ear, BK (0.01-10 nmol) produced a dose-dependent vasoconstriction. In the presence of 30 nM FR173657, the effects of BK were reduced by at least 60%, while FR173657 completely abolished the effects of all BK doses at 300 nM. FR173657 did not affect vasoconstriction induced by noradrenaline or angiotensin II. 7. The arterial injection of BK (10 nmol) into the rabbit isolated perfused ear caused an approximately three fold increase in the release of the prostaglandins E2 and I2 into the venous effluent. The BK-stimulated prostaglandin release was completely abolished in the presence of FR173657 (300 nM) while the basal prostaglandin release was unchanged. 8. In summary, FR173657 was shown to be a highly potent and selective BK antagonist which was active on B2, but not B1, receptors. FR173657 was a competitive antagonist in the rat uterus but showed a deviation from competitive inhibition in the other preparations studied similar to other second generation peptide antagonists. The inhibitory action in vitro was long-lasting, but was fully reversible.

Is there more than one prostaglandin E receptor subtype mediating hyperalgesia in the rat hindpaw?

Five synthetic prostaglandin E analogs (11-deoxyPGE1, 17-phenyl-ol-trinor prostaglandin E2, enisoprost, MB28767 and misoprostol) have been evaluated for their ability to produce mechanical hyperalgesia in rats. The Randall-Selitto paw withdrawal model of mechanical hyperalgesia was used. Following intradermal injections (2.5 microliters) into the dorsal surface of the hindpaw, each prostaglandin E analog produced a dose-dependent (1-1000 ng) decrease in nociceptive threshold (i.e. hyperalgesia). Hyperalgesia produced by 17-phenyl-ol-trinor prostaglandin E2 and MB28767, was inhibited by the prostaglandin E1 antagonist SC19220 (7.5 ng), while the hyperalgesia produced by 11-deoxyprostaglandin E1, enisoprost and misoprostol was not inhibited by this antagonist. Hyperalgesia produced by all five analogs was significantly attenuated or completely blocked by inhibiting stimulatory guanine nucleotide-binding regulatory protein with guanosine 5'-O-(2-thiodiphosphate), adenylyl cyclase with 2'5'-dideoxyadenosine and protein kinase A with WIPTIDE. These results suggest the presence of more than one prostaglandin E-receptor subtype, which mediate hyperalgesia, predominantly via the cAMP second messenger system, in the hindpaw of the rat.

Comparison of prostaglandin E1- and prostaglandin E2-induced hyperalgesia in the rat

We have studied prostaglandin E1-induced mechanical hyperalgesia in the rat hindpaw, by assessing paw-withdrawal thresholds, before and after injecting prostaglandin E1 alone or with other agents, in normal and streptozotocin-induced diabetic rats. In normal and diabetic rats, prostaglandin E1 (1-1000 ng) produced a dose-dependent decrease in mechanical nociceptive threshold. In diabetic rats, prostaglandin E1 was more potent than in normal rats, in producing hyperalgesia, whereas prostaglandin E2 hyperalgesia was not changed in normal and diabetic rats. Prostaglandin E1-induced hyperalgesia was not inhibited by E-type 1 prostaglandin receptor antagonists, SC19220 or SC51089, either in normal or diabetic rats. In fact, in the presence of SC19220, prostaglandin E1 produced enhanced hyperalgesia, in normal rats. Prostaglandin E1 hyperalgesia was not significantly modified by sympathectomy or indomethacin. Unlike prostaglandin E2, prostaglandin E1 hyperalgesia was not blocked by the inhibitor of the stimulatory guanine nucleotide-binding regulatory protein, guanosine 5'-O-(2-thiodiphosphate). It is suggested that prostaglandin E1 decreases primary afferent nociceptive threshold directly, by activating a prostaglandin receptor other than the E-type 1 prostaglandin receptor, and that this receptor is not coupled to a stimulatory guanine nucleotide-binding regulatory protein.

Clinical evaluation of H1-receptor and H2-receptor antagonists for acute postoperative pain

The acute analgesic activity of an H1-histamine antagonist, terfenadine 60 mg, and an H2-histamine antagonist, ranitidine 150 mg, were compared with ibuprofen 600 mg and placebo in a double-blind, placebo-controlled, parallel-group study. Treatments were administered to a total of 127 patients 1 hour before oral surgery. Analgesia was assessed every 30 minutes for 240 minutes after surgery. Analgesic efficacy was compared using the following standard pain intensity scales: visual analog scale, category, graphic rating, and global evaluation. Ibuprofen was significantly better than all other treatments for all measures of analgesic activity. The effects of terfenadine and ranitidine were similar to placebo. These data indicate that pretreatments with a single dose of a histamine receptor antagonist specific for either the H1- or H2-receptor does not produce analgesia in an oral surgery model of acute pain with overall assay sensitivity, suggesting that antihistamines that act primarily at peripheral sites are devoid of analgesic activity. These data contrast with other studies that have demonstrated analgesia using centrally acting antihistamines such as hydroxyzine, phenyltoloxamine, or orphenadrine.

Neural mechanisms of hyperalgesia

Hyperalgesia, or enhanced sensitivity to pain, is a symptom often associated with inflammation, nerve injury and various diseases. Although hyperalgesia appears to be mediated by sensitization of peripheral and central pain-signalling neurons, underlying mechanisms of sensitization are not well understood. Recent contributions to our knowledge of the mechanisms underlying hyperalgesia and sensitization are reviewed.

Serotonin is a directly-acting hyperalgesic agent in the rat

In this study, we have investigated serotonin hyperalgesia employing the mechanical paw withdrawal nociceptive threshold test in the rat. Intradermally injected serotonin was found to produce a dose-dependent hyperalgesia that was not attenuated by procedures which eliminate the known indirect mechanisms of hyperalgesia such as sympathectomy, polymorphonuclear leukocyte depletion or cyclooxygenase inhibition. In addition, the latency to onset of serotonin hyperalgesia is extremely short, with maximal hyperalgesia observed in less than 1 min, a similar temporal onset to direct-acting hyperalgesic agents such as prostaglandin E2. The results suggest, therefore, that the hyperalgesic effects of serotonin in our animal model are exerted by direct action on primary afferent neurons. Only the intradermal injection of selective serotonin (5-hydroxytryptamine; 5-HT) agonists for the 1A receptor subset (5-HT1A), (+/-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthaline hydrobromide and N,N-dipropyl-5-carboxamido-tryptamine maleate, produced dose-dependent hyperalgesia. No hyperalgesia was seen after 5-HT1B, CGS-12066B maleate and m-trifluoromethylphenyl-piperazine hydrochloride; 5-HT2+IC, alpha methyl 5HT and (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl; or 5-HT3, 2-methyl-5-hydroxytryptamine maleate and phenylbiguanide, agonists. Similarly, only the 5-HT1A antagonists, spiroxatrine and spiperone, attenuated the hyperalgesia induced by intradermally injected serotonin. 5-HT2+IC antagonists, mesulergine and ketanserin, and 5-HT3 antagonists, quipazine and 3-tropanyl-indole-3-carboxylate, did not significantly attenuate 5-HT hyperalgesia. We conclude that serotonin produces hyperalgesia by a direct action on the primary afferent neuron via the 5-HT1A subset of serotonin receptors.

Sensitizing effects of leukotriene B4 on intradental primary afferents

Previous studies have established that leukotriene B4 (LTB4) sensitizes cutaneous nociceptors. In this study the effects of LTB4 on spontaneous and stimulus-evoked nerve activity from primary afferents innervating the dentin of canines in adult cats were examined. LTB4 treatment (25 micrograms/ml) significantly enhanced stimulus-evoked intradental nerve activity (INA) for at least 20 min after the removal of the compound from the recording preparation. Teeth treated with LTB4 demonstrated enhanced spontaneous nerve activity following the removal of hypertonic saline used to evoked INA. These findings provide additional evidence that LTB4 is able to sensitize nociceptors and may be a long-lasting hyperalgesic factor which may contribute to pain of pulpal origin.

Prophylactic diclofenac infusions in major orthopedic surgery: effects on analgesia and acute phase proteins

The influence of diclofenac, given by continuous i.v. infusion starting preoperatively, on postoperative pain and inflammation was assessed in a double-blind, randomized, placebo-controlled study in 40 patients scheduled for major orthopedic surgery. Starting 30 min before induction the patients received either diclofenac (0.35 mg.kg-1 bolus followed by a constant-rate infusion of 90 micrograms.min-1) or placebo for 24 h. The pain intensity (VAS) and the amount of rescue narcotic (piritramide on demand) were significantly lower in the diclofenac group from 4 and 6 h postsurgery, respectively, till end of infusion. Acute phase proteins used as inflammation markers (C-reactive protein, alpha 1-chymotrypsin, alpha 1-acid glycoprotein, haptoglobin and coeruloplasmin) showed similar variations in both groups for 24 h. The diclofenac treatment had no influence on hematological and coagulation profiles, nor on muscle and liver enzymes in comparison with placebo. Both patients and observer rated the diclofenac treatment as significantly superior to the placebo treatment.

Effects of systemic non-steroidal anti-inflammatory drugs on nociception during tail ischaemia and on reperfusion hyperalgesia in rats

1. We have investigated the effects of five non-steroidal anti-inflammatory drugs (NSAIDs) on nociception during ischaemia and on reperfusion hyperalgesia in rats. 2. We induced tail ischaemia in conscious rats by applying a tourniquet at the base of the tail until the rats exhibited co-ordinated escape behaviour when we released the tourniquet. 3. We assessed hyperalgesia by measuring the tail flick latency following tail immersion in water at 49 degrees C, before applying and immediately after releasing the tourniquet, and then at 30 min intervals for 2 h. 4. Intraperitoneal injection of NSAIDs prior to applying the tourniquet had no effect on the co-ordinated escape behaviour during ischaemia, nor on tail flick latency in the absence of prior ischaemia. However all the drugs attenuated reperfusion hyperalgesia in a log dose-dependent manner. Doses required to abolish hyperalgesia, were indomethacin 5 mg kg-1, diclofenac sodium 42 mg kg-1, ibuprofen 54 mg kg-1, dipyrone 168 mg kg-1 and paracetamol 170 mg kg-1. 5. We conclude that the mechanisms underlying nociception during ischaemia are not the same as those underlying reperfusion hyperalgesia. Moreover our procedure provides a rapid and more humane method for measuring the antinociceptive potency of NSAIDs.

The effect of topical administration of indomethacin on symptoms in corneal scars and edema

We conducted a masked randomized study of 50 patients to evaluate the effect of administration of topical indomethacin 1% suspension on symptoms in corneal scars, edema, infiltrates, and erosions. Patients with symptoms (photophobia, pain, itching, burning sensation, foreign-body sensation, and tearing) were treated with topically administered indomethacin 1% or placebo and monitored for eight weeks. The severity of the complaints was rated and the scores were evaluated (Wilcoxon rank-sum test). Of the 25 patients treated with indomethacin, 21 (84%) had improvement in symptoms and the severity of each of the symptoms was significantly decreased. Of the 25 patients treated with placebo, one (4%) had improvement in symptoms without statistical change of the severity of the symptoms. However, when the placebo-treated patients received indomethacin drops, the symptoms were significantly decreased (P less than .002). This study suggests that topical administration of indomethacin 1% may reduce ocular symptoms in patients with corneal scars, edema, or erosions.

Further confirmation of the role of adenyl cyclase and of cAMP-dependent protein kinase in primary afferent hyperalgesia

Recent evidence has suggested that cAMP plays a role as a second messenger in the decrease in nociceptive threshold (or hyperalgesia) produced by agents acting on primary afferent terminals. In support of this hypothesis we report that intradermal injection of a direct activator of adenyl cyclase, forskolin, produces a dose-dependent hyperalgesia in the rat. The duration of this hyperalgesia was prolonged by the phosphodiesterase inhibitors, isobutylmethylxanthine and rolipram. Forskolin hyperalgesia was antagonized by the Rp isomer of cyclic adenosine-3'5'-monophosphothioate, an analog of cAMP that prevents the phosphorylation of the cAMP protein kinase. The Rp isomer of cyclic adenosine-3'5'-monophosphothioate also inhibited the hyperalgesia induced by a membrane-permeable analogue of cAMP, 8-bromocyclic adenosine monophosphate, as well as the hyperalgesia induced by agents that are presumed to act directly on primary afferent nociceptors: prostaglandin E2, prostaglandin I2, (8R,15S)-dihydroxyicosa(5E-9,11,13Z)tetraenoic acid; and the adenosine A2-agonist 2-phenylaminoadenosine. Although the cAMP second messenger system contributes to primary afferent hyperalgesia, we found no evidence for a contribution of protein kinase C. Thus, hyperalgesia induced by prostaglandin E2, prostacyclin (prostaglandin I2), (8R,15S)-dihydroxyicosa(5E-9,11,13Z)tetraenoic acid, the adenosine A2-agonist 2-phenylaminoadenosine, 8-bromocyclic adenosine monophosphate and the direct activator of adenyl cyclase, forskolin, were not significantly attenuated by the selective inhibition of protein kinase C by the 19-31 fragment of protein kinase C. Two other inhibitors of protein kinase C, sphingosine and staurosporine, also failed to attenuate prostaglandin E2-induced hyperalgesia.

Estimation of the in vivo effect of cyclooxygenase inhibitors on prostaglandin E2 levels in mouse brain

The purpose of the present study was to develop a biochemical marker of inhibition of cyclooxygenase in the central nervous system following oral administration of cyclooxygenase inhibitors. An ex vivo method was developed wherein the brain was removed, incubated at room temperature for 2 min permitting prostaglandins to be synthesized from spontaneously released arachidonic acid. Indomethacin, zomepirac Na, naproxen Na, ibuprofen, aspirin and acetaminophen inhibited the ex vivo production of prostaglandin E2 in a dose-related manner at doses that correlated well with both their potency to inhibit mouse brain cyclooxygenase in vitro, and their antinociceptive potency in a mouse abdominal constriction test. When the brains were frozen immediately after the mice were killed, the above drugs did not reduce the endogenous prostaglandin E2 level. Thus while cyclooxygenase inhibitors did not reduce normal prostaglandin E2 levels in brain, they did attenuate post-mortem increases in prostaglandin E2. This novel assay permits an estimate of cyclooxygenase inhibitory effects in vivo. The data further support the suggestion that many of these drugs may have a central as well as a peripheral effect.

Analgesic and antiinflammatory effects of glucamethacin (a nonsteroidal antiinflammatory analgesic) after the removal of impacted third molars

A double-blind study was undertaken to compare the effects of glucamethacin, aspirin, and placebo in the control of pain, trismus, and postoperative swelling of 59 outpatients who underwent the surgical removal of impacted lower third molars. Aspirin (1000 mg three times a day) was superior to placebo in one of the analgesic parameters studied, whereas glucamethacin (140 mg three times a day) was not superior to placebo. Both drugs significantly reduced the occurrence of trismus on the day after surgery, but no differences with placebo were found 48 hours postoperatively. In the study of postoperative swelling, no significant differences were found between the medications and the placebo in the postoperative period. It is concluded that glucamethacin, a nonsteroidal antiinflammatory drug, produces a minimal analgesic effect and does not relieve postoperative swelling in the dental patient undergoing surgical removal of impacted third molars.

Mediation of primary afferent peripheral hyperalgesia by the cAMP second messenger system

Cyclooxygenase (prostaglandin E2 and prostaglandin I2) and lipoxygenase [8(R), 15(S)-dihydroxyicosa-(5E-9,11,13Z)-tetraenoic acid] products of arachidonic acid metabolism are thought to produce peripheral hyperalgesia by a direct action on the primary afferent nociceptor. In this study we investigated the possibility that these eicosanoids generate hyperalgesia through a common second messenger in the rat. We report that 8-bromo cAMP, a membrane permeable analogue of cAMP, produces a dose-dependent hyperalgesia that is not affected by treatments that interrupt indirect routes of hyperalgesia production including sympathectomy with 6-hydroxydopamine, depletion of polymorphonuclear leukocytes (a source of hyperalgesic eicosanoids) with hydroxyurea, or blockade of the cyclooxygenase pathway of arachidonic acid metabolism with indomethacin. The phosphodiesterase inhibitor isobutyl-methylxanthine markedly prolongs the hyperalgesic effect of 8-bromo cAMP as well as those of the directly acting hyperalgesic agents prostaglandin E2, prostaglandin I2 and 8(R),15(S)-dihydroxyicosa-(5E-9,11,13Z)-tetraenoic acid. We conclude that the effect of all known hyperalgesic eicosanoids is mediated by the cAMP second messenger system and suggest, therefore, that cAMP mediates peripheral hyperalgesia in primary afferent nociceptors.

Characterization of the arachidonic acid metabolites mediating bradykinin and noradrenaline hyperalgesia

It has been suggested that bradykinin (BK) and norepinephrine (NE) induce hyperalgesia, indirectly, by stimulating the production of prostaglandin products of the cyclo-oxygenase pathway of arachidonic acid metabolism. However, the specific PGs that mediate the hyperalgesic effects of BK and NE are unknown. Two endogenous PGs, prostaglandin E2 (PGE2) and prostacyclin (PGI2) are known to produced hyperalgesia. Since the hyperalgesic effects of PGE2 and PGI2 can be distinguished by the duration of the hyperalgesia they induce, we have compared the duration of BK and NE hyperalgesia with those of PGE2 and PGI2. To further address the type of PG mediating BK and NE hyperalgesia, we have evaluated the ability of SC19220, a PG-receptor antagonist, to distinguish the hyperalgesia induced by PGE2 and PGI2. BK induces hyperalgesia with duration similar to that of PGE2. NE induces hyperalgesia with duration similar to that of PGI2. SC19220, at low doses, antagonizes PGE2 and BK hyperalgesia but not PGI2 and NE hyperalgesia. These data are compatible with the suggestion that the prostaglandin products mediating BK and NE hyperalgesia differ, BK hyperalgesia being mediated by PGE2 and NE hyperalgesia by PGI2.

Hyperalgesia onset latency suggests a hierarchy of action

Hyperalgesia onset latencies of inflammatory mediators were quantified by measuring the threshold of the nociceptive flexion reflex in the rat at 1 min intervals after intradermal injection. Prostaglandin E2 and 8(R), 15(S)-dihydroxyicosa-(5E,9,11,13Z)-tetraenoic acid induced hyperalgesia with short onset latencies, compatible with a direct action on primary afferent nociceptors. Bradykinin, norepinephrine and leukotriene B4 induced hyperalgesia with a significant delay in onset, compatible with their known indirect mechanisms of producing hyperalgesia. We propose that use of this approach, rapid frequent measurement of nociceptive threshold, can be used to determine the hierarchy of action of mediators in hyperalgesic mechanisms.

Regulatory mechanisms for substance P in the dorsal horn during a nociceptive stimulus: axoplasmic transport vs electrical activity

Substance P (SP) is believed to be a neuromediator of nociception in the dorsal horn of the spinal cord. SP precursor is synthesized in the dorsal root ganglia (DRG) and transported via axoplasmic transport to the nerve terminal where it is stored and released as SP. The chemical nociceptive stimulus, formalin, when injected into the hindpaw causes an increase in the level of SP in the dorsal horn. This increase in SP may be the result of increased electrical activity due to activation of free nerve endings or the transport of some chemical or trophic signal to the DRG or to the central terminal. This study investigates the mechanism of the SP increase during the formalin stimulus. Rats were anesthetized and a laminectomy performed. In some experiments the sciatic nerve was exposed. Agar gel pads containing either colchicine or tetrodotoxin (TTX) were applied to the dorsal root or sciatic nerve prior to the injection of 5% formalin or saline into the hindpaw. Electrical activity across the dorsal root distal to the gel pad was monitored to determine the effects of colchicine and TTX on the nerve. Sixty min after the injection into the hindpaw, the animal was perfused and the lumbar spinal cord removed. Ten-micron frozen sections were stained for SP. It was found that the formalin-evoked increase in SP could be partially blocked by either colchicine or TTX applied to the dorsal root and completely blocked by the application of both agents together. TTX or colchicine applied to the sciatic nerve completely blocked the formalin-evoked increase in SP.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of dental pain by the preoperative administration of flurbiprofen

In a series of three studies involving dental outpatients undergoing removal of impacted third molars, preoperative and postoperative administration of flurbiprofen (Ansaid, Upjohn) led to superior pain relief when compared with acetaminophen alone or in combination with oxycodone. Patient preference and global evaluations clearly favored flurbiprofen. Side effects were mild and generally more common in patients receiving the opiate/mild analgesic combination. In two additional studies, flurbiprofen and etidocaine, a long-acting local anesthetic, also resulted in significantly less postoperative pain than a combination of acetaminophen/oxycodone and lidocaine; 67 percent of patients in the flurbiprofen plus etidocaine group reported no or only slight pain during the entire observation period. The greater analgesic efficacy of flurbiprofen appears to represent a genuine therapeutic advantage, since it is not achieved at the expense of greater side effects.

Relevance of prostaglandins in migraine

Prostaglandins (PG), particularly PGE, may be linked to the pathophysiology of migraine in several important ways. PGE1 may "simulate" a migraine attack in healthy volunteers. PGE may be elevated in patients with migraine. In animal experiments and in human infusions, PGEs cause vasodilation and hyperalgesia, both typical reactions of inflammation. The view that vascular headache is an "inflammatory reaction" allows the best concept concerning the local role of PGs and the effectiveness of PG-inhibitors in the treatment of migraine. The local role of PGs may provide a common denominator in several hormonal, neural and other influences on vessels. The common triggers of a migraine attack like menstruation, alcohol and stress influence the PG-system and even the dietary reactions, hormonal influences, sleep and reserpine have some connections with the PG-system. A local role for PGs does not diminish the importance of other pathophysiological mechanisms operating during an attack. On the contrary, PGs may fill in gaps in our understanding of how the overt pain of attacks is produced.

The arachidonic acid cascade. The prostaglandins, thromboxanes and leukotrienes

Certain polyunsaturated fatty acids, such as arachidonic acid, are metabolized by oxygenation into a large family of biologically active substances, the prostanoids. These include the prostaglandins, thromboxanes, prostacyclins, leukotrienes and also a number of related compounds. Oxygenation can take place at many different positions of arachidonic acid. A cyclo-oxygenase introduces oxygen at C-11 and converts the resulting peroxy compound into a 9, 11-endoperoxide structure. The cyclic peroxides thus formed, PGG2 and PGH2, are highly potent compounds and are the immediate precursors of the prostaglandins, thromboxanes and prostacyclin. Other enzymes, the lipoxygenases, may instead introduce oxygen at C-5, C-8, C-9, C-12 or C-15: further conversions from, for example, the initially formed 5- or 15-hydroperoxy acids may lead to the leukotrienes. The prostanoids display strong and varied biological activities, and have effects on numerous processes in the body. In some pathological conditions the prostanoids play important roles. For example, certain products of the arachidonic acid cascade are considered to be mediators of the inflammatory response: they are formed during the process, contribute to the symptoms of erythema, vascular leakage, fever, pain and chemotaxis, and inhibition of their biosynthesis can be achieved at different levels by the anti-inflammatory drugs.

Prostaglandin release and nociceptor stimulation by peptides

The effects of substance P, somatostatin, vasoactive intestinal polypeptide, cholecystokinin octapeptide, eledoisin and bombesin on release and metabolism of incorporated (1-14C)-arachidonic acid was investigated in the isolated rabbit ear. The influence of eledoisin and bombesin on release of prostaglandins was compared with that of bradykinin (Sametz and Juan 1982). Only eledoisin and bombesin stimulated the release of prostaglandins I2 and E2 but with a lesser potency than bradykinin. Only eledoisin in a high dose stimulated nociceptors per se whereas bombesin did not. Eledoisin and bombesin in a low dose enhanced nocicpetion induced by acetylcholine in the rabbit ear; this enhancement of the algesic effect of acetylcholine was abolished by indometacin which indicates a sensitization of nociceptors by released prostaglandins. Although effects of eledoisin and bombesin are mediated at least in part by released prostaglandins, the nociceptor-stimulating and prostaglandin-releasing potency of bradykinin remaines unique among all peptides tested so far.

Suppression of postoperative pain by the combination of a nonsteroidal anti-inflammatory drug, flurbiprofen, and a long-acting local anesthetic, etidocaine

The analgesic efficacy of the combination of a nonsteroidal anti-inflammatory drug, flurbiprofen, and a long-acting local anesthetic, etidocaine, was evaluated for the suppression of acute postoperative pain. Subjects having two impacted third molars removed at two appointments received either the experimental combination or standard treatment in a randomized, crossover design. The experimental treatment consisted of 100 mg flurbiprofen 30 minutes before surgery, 1.5% etidocaine with 1:200,000 epinephrine five minutes before surgery, and 100 mg flurbiprofen three hours after surgery. Standard treatment consisted of 10 mg oxycodone plus 650 mg acetaminophen 30 minutes before surgery, 2% lidocaine with 1:100,000 epinephrine five minutes before surgery, and a second dose of the oxycodone-acetaminophen combination three hours after surgery. Pain intensity was rated hourly from one to seven hours after surgery, using a variety of ordinal and analog scales. The flurbiprofen-etidocaine combination resulted in significantly less postoperative pain than the oxycodone plus acetaminophen-lidocaine combination on all four analgesic scales used and was preferred by the majority of the patients. This study shows that pretreatment with a nonsteroidal anti-inflammatory drug, flurbiprofen, in combination with a long-acting local analgesic, etidocaine, suppresses pain to a greater extent than a potent opiate mild/analgesic combination and lidocaine without an increase in side-effect liability.

Suppression of postoperative pain by preoperative administration of ibuprofen in comparison to placebo, acetaminophen, and acetaminophen plus codeine

The analgesic effect of preoperatively administered ibuprofen was evaluated in 107 dental outpatients undergoing the removal of impacted third molars. Subjects were given 800 mg ibuprofen prior to the procedure and 400 mg ibuprofen 4 and 8 hours later. Comparison was made to groups receiving either placebo at all three doses, 600 mg acetaminophen administered on the same schedule, or preoperatively administered placebo followed by two doses of postoperatively administered 600 mg acetaminophen plus 60 mg codeine. Ibuprofen pretreatment resulted in significantly less pain than placebo or acetaminophen pretreatment as the local anesthetic wore off. Ibuprofen also resulted in less postoperative pain than acetaminophen plus codeine following the second dose. Side effects were similar across drug treatments and placebo with the exception of greater reports of drowsiness following the opiate-analgesic combination. These findings indicate that pretreatment with a nonsteroidal antiinflammatory drug, such as ibuprofen, results in a suppression of postoperative pain when compared to standard therapy without an increase in side effects.

Sensitization of group IV muscle receptors to bradykinin by 5-hydroxytryptamine and prostaglandin E2

The aim of the study was to find out whether endogenous substances with a presumed sensitizing action on nociceptors alter the chemical excitability of muscle receptors with unmyelinated afferent fibres. In anaesthetized cats, the discharges of single group IV units in response to intra-arterial injections of bradykinin were evaluated quantitatively and the influence of 5-hydroxytryptamine (5-HT) and prostaglandin E2 (PGE2) on the response magnitude determined. Both 5-HT and PGE2 enhanced the bradykinin sensitivity of most of the muscle receptors, i.e. the receptors were sensitized to bradykinin by 5-HT and PGE2. Units that were activated by bradykinin before administration of the sensitizing chemicals showed an increase in response magnitude; in receptors not responding to the standard dose of bradykinin an activation often occurred after chemical sensitization. It is occurred that under the influence of elevated tissue levels of 5-HT and PGE2 the afferent impulse activity induced in group IV muscle receptors by bradykinin will be higher. As the substances used are released together from pathologically altered organs and since many of the group IV muscle receptors are considered to be nociceptive, the chemical sensitization of these receptors to the algesic agent bradykinin might play a role in the production of pain in an inflamed or injured muscle.

Histamine-induced release of arachidonic acid and of prostaglandins in the peripheral vascular bed: mode of action

1. Injection or infusion of histamine intraarterially into the isolated perfused rabbit ear dose-dependently stimulated the release of prostaglandins (PGs) as measured by radioimmunoassay (PGE), bovine coronary artery strips (PGI2) and by the prelabeling technic with [1-14C]-arachidonic acid (PGI2, PGE2, PGF2 alpha, PGD2). 2. PG release was abolished by indometacin (1-3 microgram/ml) and reduced by the phospholipase A2 inhibitor quinacrine (10 microgram/ml) as well as by perfusing with calcium-free, 1 mM EGTA containing solution. 3. The histamine H2-receptor antagonists burimamide (5 microgram/ml) and cimetidine (2 microgram/ml) did not influence histamine-induced PG release. The H1-receptor antagonist mepyramine (0.1-1 microgram/ml) abolished histamine-induced mepyramine (0.1-1 microgram/ml) abolished histamine-induced PG release. 4. In the presence, but not in the absence, of bovine serum albumin there was a basal release of high amounts of arachidonic acid. Histamine tended to increase the released amount of radioactive arachidonic acid. In contrast to indometacin which only blocked PG release, mepyramine significantly reduced the histamine-stimulated release of arachidonic acid, too. 5. The results show that in the peripheral vascular bed, histamine, via H1-receptors, activates a phospholipase A2 mainly by increasing a transfer of extracellular calcium into the cell. Activation of a phospholipase A2 results in the release of arachidonic acid possibly from a rather small endogenous pool which specifically provides substrate for the PG synthetase system.