Role of nitric oxide on the increased vascular permeability and neutrophil accumulation induced by staphylococcal enterotoxin B into the mouse paw

The role of nitric oxide (NO) on the increase in vascular permeability and neutrophil migration induced by staphylococcal enterotoxin B (SEB; 25 microgram/paw) in the mouse was investigated in this study. The NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) [but not its inactive enantiomer N(omega)-nitro-D-arginine methyl ester (D-NAME)], given intravenously (25-100 micromol/kg) or subplantarly (0.25-1.0 micromol/paw), reduced SEB-induced paw oedema significantly. A similar response was observed with aminoguanidine, given either intravenously (200-600 micromol/kg) or subplantarly (2 micromol/paw). In contrast to paw oedema, the plasma exudation in response to SEB was not affected by the subplantar injection of L-NAME or aminoguanidine. The inhibition of oedema and plasma exudation by systemic treatment with L-NAME or aminoguanidine was reversed by co-injection of the vasodilator iloprost (0.3 nmol/paw). Subplantar injection of SEB (25 microgram/paw) increased by 69% the myeloperoxidase (MPO) activity of SEB-treated paws, indicating the presence of neutrophils. Intravenous (12.5-50 micromol/kg) or subplantar (0.125-0.5 micromol/paw) administration of L-NAME (but not of its inactive enantiomer, D-NAME) largely reduced the MPO activity in SEB-treated paws. Similarly, intravenous (200-600 micromol/kg) or subplantar (2 micromol/paw) administration of aminoguanidine significantly reduced the MPO values of the SEB-injected paws. The vasodilator iloprost (0.3 nmol/paw) completely reversed the inhibition by L-NAME or aminoguanidine of the MPO activity in SEB-injected paws. Our results show that the increased vascular permeability and neutrophil accumulation in response to subplantar injection of SEB in the mouse are inhibited by L-NAME and aminoguanidine by mechanisms probably involving reduction of local microvascular blood flow.     

Intraplantar morphine depresses spinal c-Fos expression induced by carrageenin inflammation but not by noxious heat.

1. We have studied the effects of intraplantar administration of the same doses of morphine on intraplantar carrageenin (6 mg 150 microliters-1 of saline) and noxious heat (52 degrees C for 15 s) induced spinal c-Fos expression and inflammation. 2. Intraplantar carrageenin, in awake rats, induced numerous Fos-like immunoreactive (Fos-LI) neurones in the dorsal horn of L4-L5 lumbar segments of the spinal cord and extensive peripheral oedema. At 1 h 30 min, Fos-LI neurones were preferentially located in the superficial laminae (74 +/- 2%) whereas at 3 h, Fos-LI neurones were observed both in the superficial (45 +/- 2%) and deep (37 +/- 1%) laminae of the spinal dorsal horn. 3. Intraplantar morphine dose-dependently reduced c-Fos expression induced 1 h 30 min after carrageenin (r = 0.605, P < 0.02), these effects were completely blocked by intraplantar methiodide naloxone (20 micrograms) (121 +/- 22% of control carrageenin expression). The systemic injection of the highest dose of intraplantar morphine (50 micrograms) had no significant effect on the number of Fos-LI neurones (88 +/- 9% of control carrageenin expression). None of the drugs influenced unilateral peripheral oedema observed 1 h 30 min after carrageenin. 4. In the second series of experiments, intraplantar morphine dose-dependently reduced the number of superficial and deep Fos-LI neurones induced 3 h after carrageenin (r = 0.794, P < 0.0004 and r = 0.698, P < 0.004, respectively). Furthermore, the effects of the highest dose of intraplantar morphine were completely blocked by co-administration of intraplantar methiodide naloxone (20 micrograms). 5. In addition, intraplantar morphine dose-dependently reduced the ankle (r = 0.747, P < 0.002) and paw (r = 0.682, P < 0.005) oedema observed 3 h after carrageenin, with the effect of the highest dose of intraplantar morphine being completely blocked by co-administration of methiodide naloxone (98 +/- 4% and 102 +/- 8% of control paw and ankle oedema, respectively). 6. Brief noxious heat stimulation, in urethane anaesthetized rats, induced, 2 h after the stimulation, numerous Fos-LI neurones in the dorsal horn of L3-L4 lumbar segments of the spinal cord but no detectable peripheral oedema. Fos-LI neurones were preferentially located in superficial laminae (94 +/- 2%) of the spinal dorsal horn. None of the drugs influenced the noxious heat induced c-Fos expression. 7. Such results illustrate that peripheral effects of morphine preferentially occur during inflammatory states and outline the interest of extending clinical investigations of the possible use of local injection of morphine in various inflammatory pain states.     

Converting enzyme inhibition in the rat by captopril is accompanied by potentiation of carrageenin-induced inflammation.

Hind paw oedema in rats, measured by plethysmography or extravasation of Evans Blue dye into the skin, after subplantar injection of submaximal doses of carrageenin (1-100 micrograms) was significantly increased for 4 h during kininase II inhibition with captopril (1 mg kg-1, s.c.). Submaximal oedema, as assessed by paw swelling, after subplantar bradykinin (0.1-1.0 microgram) was also significantly increased after subcutaneous administration of this dose of captopril, whereas that in response to either histamine (2-20 micrograms) or prostaglandin E2 (2 micrograms) was unchanged. The pain threshold of the paw, injected with carrageenin (1 microgram) was lowered significantly after subcutaneous administration of captopril (1 mg kg-1). Potentiation by captopril (1 mg kg-1, s.c.) of paw swelling in response to intraplantar carrageenin (100 micrograms) or bradykinin (1 microgram) was reduced by prior subcutaneous administration of indomethacin (5 mg kg-1). It is suggested that normally, tissue kininase II activity is sufficient to decrease the inflammatory response of the hind paw to carrageenin or bradykinin. After inhibition of kininase II with captopril, bradykinin levels are increased and interact with concomitantly released prostaglandins to potentiate inflammation.     

Local inhibition of inflammatory pain by naloxone and its N-methyl quaternary analogue

Inflammation was induced in rats by intraplantar administration of carrageenan (500 micrograms in 0.1 ml). Nociceptive thresholds were measured on both inflamed and contralateral hindpaws with the pressure test of Randal and Sellito. Low doses (0.03-10 micrograms/kg) of naloxone hydrochloride (Nx) or of methylnaloxone methylsulfonate (MeNx) were injected 4 h after carrageenan in the inflamed paw: Nx (3 micrograms) and MeNx (1-10 micrograms) diminished inflammatory pain; a slight, nonspecific hyperalgesia was observed in the contralateral paw after Nx, MeNx or NaCl. Neither drug was effective when injected s.c. at the same doses and time; however activities were shown to be influenced by the experimental schedule. Low s.c. doses of Nx antagonized the analgesia produced by s.c. morphine whereas MeNx did not. This work demonstrates the local site of the analgesic action of the doses of Nx and MeNx used here, bringing new evidence in favour of the existence of cutaneous opioid receptors. Opiate antagonists might inhibit inflammatory pain by interacting with a particular population of cutaneous receptors and (or) by being dealkylated locally into agonists.     

Inhibition and induction of drug metabolism by psoralens: alterations in duration of sleep induced by hexobarbital and in clearance of caffeine and hexobarbital in mice.

1. Hexobarbital (100 mg/kg i.p.) sleeping times in male CD-1 mice pretreated (-1 h) with a single i.p. injection of 150 mumol/kg of psoralen or coumarin analogues were increased, most markedly (6-fold) by linear, methoxy-substituted psoralens. 2. Hexobarbital sleeping times of mice which received three daily injections (231 mumol/kg; 50 mg/kg) of 8-methoxypsoralen (8-MOP) were 44% of controls (corn oil). 3. The whole-body half-life of caffeine (1 mg) in mice was 10.2, 1.2, and 0.37 h following 8-MOP (50 mg/kg per day) x 1, vehicle, and 8-MOP x 3 respectively. 4. The whole-body concentrations of hexobarbital (100 mg/kg dose) in mice 30 min after dosing were 14.3 +/- 0.9, 8.4 +/- 0.3, and 5.2 +/- 0.5 micrograms/ml (1 mouse = 150 ml) following 8-MOP (50 mg/kg per day) x 1, vehicle, and 8-MOP x 3 respectively. 5. It is concluded that, administered acutely, psoralen analogues inhibit hexobarbital metabolism in mice; and 8-MOP administered acutely inhibits the metabolism of caffeine and hexobarbital, but administered repeatedly increases their metabolism.     

Restoration by levamisole of endotoxin-inhibited neutrophil migration, oedema and increased vascular permeability induced by carrageenin

Intravenous administration of E. coli lipopolysaccharide (LPS) inhibited the migration of neutrophils into the pleural cavity that occurs following challenge with intrapleural carrageenin. Treatment of animals with levamisole (10 mg/kg i.p.) 30 min after the intravenous administration of LPS almost restored carrageenin-induced neutrophil migration to control levels without affecting the number of circulating neutrophils. Intravenous administration of LPS (30 micrograms/kg) blocked neutrophil migration in vivo and significantly reduced the oedema and the increased vascular permeability induced by intraplantar administration of carrageenin. These LPS effects were partly counteracted by levamisole (10 mg/kg) given 30 min after LPS. Intravenous LPS did neither affect oedema nor the increase in vascular permeability induced by intraplantar administration of dextran. It is suggested that (a) the exudation and oedema formation induced by carrageenin partially depend upon migrating neutrophils and (b) inhibition of cell migration by circulating LPS may constitute an important contributing factor in septicaemia. Levamisole restores both cell migration and vascular inflammatory events inhibited by circulating LPS.     

Effect of resiniferatoxin on the noxious heat threshold temperature in the rat: a novel heat allodynia model sensitive to analgesics

1. An increasing-temperature hot plate (ITHP) was introduced to measure the noxious heat threshold (45.3+/-0.3 degrees C) of unrestrained rats, which was reproducible upon repeated determinations at intervals of 5 or 30 min or 1 day. 2. Morphine, diclofenac and paracetamol caused an elevation of the noxious heat threshold following i.p. pretreatment, the minimum effective doses being 3, 10 and 200 mg kg(-1), respectively. 3. Unilateral intraplantar injection of the VR1 receptor agonist resiniferatoxin (RTX, 0.048 nmol) induced a profound drop of heat threshold to the innocuous range with a maximal effect (8-10 degrees C drop) 5 min after RTX administration. This heat allodynia was inhibited by pretreatment with morphine, diclofenac and paracetamol, the minimum effective doses being 1, 1 and 100 mg kg(-1) i.p., respectively. 4. The long-term sensory desensitizing effect of RTX was examined by bilateral intraplantar injection (0.048 nmol per paw) which produced, after an initial threshold drop, an elevation (up to 2.9+/-0.5 degrees C) of heat threshold lasting for 5 days. 5. The VR1 receptor antagonist iodo-resiniferatoxin (I-RTX, 0.05 nmol intraplantarly) inhibited by 51% the heat threshold-lowering effect of intraplantar RTX but not alpha,beta-methylene-ATP (0.3 micromol per paw). I-RTX (0.1 or 1 nmol per paw) failed to alter the heat threshold either acutely (5-60 min) or on the long-term (5 days). The heat threshold of VR1 receptor knockout mice was not different from that of wild-type animals (45.6+/-0.5 vs 45.2+/-0.4 degrees C). 6. In conclusion, the RTX-induced drop of heat threshold measured by the ITHP is a novel heat allodynia model exhibiting a high sensitivity to analgesics.     

Effects of loperamide on mechanical allodynia induced by herpes simplex virus type-1 in mice

In the present study, we investigated whether the peripherally acting micro-opioid receptor agonist loperamide would inhibit allodynia in the non-inflamed dermatome of mice with herpetic pain. Subcutaneous (s.c.) injection of loperamide (1 and 3 mg/kg) inhibited allodynia. Local (intraplantar) injection of loperamide (1 and 5 microg/site) also produced an anti-allodynic effect. The peripheral opioid receptor antagonist naloxone methiodide (0.1 mg/kg, s.c.) and the micro-opioid receptor-selective antagonist beta-funaltrexamine (40 nmol/site, intraplantar and 20 mg /kg, s.c.) antagonized the anti-allodynic effects of systemic and local loperamide. Local injection of loperamide into the contralateral hind paw was without effect, suggesting that the effect is mediated through local action, not systemic action. Acute and subacute tolerance did not develop to the anti-allodynic effect of loperamide. In addition, there were no cross-tolerance between local opioids (morphine and loperamide) and systemic morphine. These results suggest that stimulation of peripheral micro-opioid receptors suppresses herpetic allodynia without tolerance development. The non-narcotic micro-opioid receptor agonist loperamide may relieve acute herpetic pain in patients with herpes zoster.     

Relevance of tumour necrosis factor-alpha for the inflammatory and nociceptive responses evoked by carrageenan in the mouse paw

1. The present study evaluated the participation of tumour necrosis factor-alpha (TNF-alpha) in the inflammatory and nociceptive responses evoked by carrageenan in the mouse paw. 2. The intraplantar injection of carrageenan (300 microg paw-1) induced a marked and biphasic paw oedema formation (peaks at 6 and 72 h), which was accompanied by a long-lasting mechanical allodynia (that remained elevated for up to 72 h) and a significant increase of myeloperoxidase (MPO) activity (peak at 6 h) in both Swiss and C57/BL6 mice. 3. The paw oedema, the elevation of MPO activity and to a lesser extent the mechanical allodynia elicited by carrageenan were found to be significantly reduced in TNF-alpha p55 receptor knockout mice. 4. Of interest, the systemic administration of an anti-TNF-alpha antibody produced a significant inhibition of paw oedema, mechanical allodynia and MPO activity. A noteworthy decrease in inflammatory and nociceptive responses caused by carrageenan was also observed when mice were previously treated with the preferential inhibitor of TNF-alpha synthesis, thalidomide. 5. The present results clearly indicate that the proinflammatory cytokine TNF-alpha plays a critical role in the oedema formation, as well as in the mechanical allodynia and the neutrophil migration, following carrageenan administration into the mouse paw. Intraplantar injection of carrageenan in mice could constitute a useful model for assessment of the in vivo effects of potential inhibitors of TNF-alpha-related pathways.     

Estrogen treatment to ovariectomized rats modifies morphine-induced behavior

Two weeks after surgery, ovariectomized (OVX) rats were treated for 3 days with either 17 beta-estradiol (10 or 100 micrograms/kg, SC, per day) or the oil vehicle. They were then tested for morphine-induced hyperactivity (4 mg/kg, IP), analgesia and catalepsy (15 and 20 mg/kg, IP) 24 or 72 hr after the last steroid or oil injection. Estradiol treatment did not affect the locomotion or the sensitivity to nociceptive stimuli of OVX rats and did not induce a cataleptic state in animals. Estradiol- (100 micrograms/kg) treated OVX rats exhibited attenuated morphine-induced hyperlocomotion regardless of the time that had elapsed after estradiol treatment cessation, attenuated morphine-induced catalepsy at 24 hr after estradiol treatment and unaltered morphine-induced analgesia. OVX rats treated with a lower estradiol dose (10 micrograms/kg) exhibited significantly increased morphine-induced analgesia and slightly increased catalepsy. The results show that the sensitivity of brain opiate systems controlling some of the behavioral effects of morphine is modified following estradiol treatment to OVX rats.     

Antinociceptive mechanism of Gosha-jinki-gan in streptozotocin-induced diabetic animals: role of nitric oxide in the periphery

Using streptozotocin-induced diabetic mice and rats, we evaluated the antinociceptive mechanism of Gosha-jinki-gan. The antinociceptive effect of Gosha-jinki-gan (0.3 g/kg, p.o.) in diabetic mice, as determined by the tail-pressure test, was inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 2, 5 mg/kg, i.p.). When L-NAME (10 microg) or methylene blue (500 microg) was topically administered to the intraplantar area of the hind paw, the region used for the paw-pressure test, the antinociceptive activity of Gosha-jinki-gan (0.3 g/kg, p.o.) in diabetic rats was decreased. These results suggested that the antinociceptive effect of Gosha-jinki-gan partly resulted from the peripheral action of increasingly produced nitric oxide.     

Anti-allodynic action of the tormentic acid,a triterpene isolated from plant,against neuropathic and inflammatory persistent pain in mice

Experiments were designed to address whether the pentacyclic triterpene tormentic acid isolated from the stem bark of the plant Vochysia divergens exerts oral anti-allodynic properties in two models of chronic pain in mice: neuropathic pain caused by partial ligation of the sciatic nerve and inflammatory pain produced by intraplantar injection of Complete Freund's Adjuvant. Oral administration of tormentic acid (30 mg/kg) twice a day for several consecutive days produced time-dependent and pronounced anti-allodynia effect in both ispsilateral and contralateral paws after plantar injection of Complete Freund's Adjuvant. The inhibition observed was 82+/-9% and 100+/-11%, respectively. Interestingly, tormentic acid did not inhibit paw oedema formation following Complete Freund's Adjuvant plantar injection. Tormentic acid (30 mg/kg, p.o.) and gabapentin (70 mg/kg, p.o.), given twice a day, inhibited markedly the neuropathic allodynia induced by partial ligation of the sciatic nerve, with inhibition of 91+/-19% and 71+/-16%, respectively. The anti-allodynic action of tormentic acid was not associated with impairment of the motor activity of the animals. Together, the present results indicate that tormentic acid or its derivatives might be of potential interest in the development of new clinically relevant drugs for the management of persistent neuropathic and inflammatory allodynia.     

Homologous tachyphylaxis to bradykinin and its interference with allergic pleurisy in actively sensitized rats.

After recovery from a first intraplantar or intrathoracic stimulation with bradykinin, repeated daily provocation with this peptide resulted in a progressive loss of its ability to cause paw or pleural oedema, reaching 0-20% of the control within seven and four consecutive provocations, respectively. The phenomenon was shown to be time reversible, since the unresponsiveness ceased when stimulations were discontinued, and localized, since paw oedema evoked by the peptide was not modified after desensitization of either the contralateral paw or the pleural cavity. Furthermore desensitization to bradykinin did not influence the pleurisy elicited by either histamine (200 micrograms/cavity), 5-hydroxytryptamine (5-HT) (100 microgram/cavity) or platelet-activating factor (PAF) (1 microgram/cavity), suggesting that the desensitization was selective. In contrast, when actively sensitized animals were submitted to bradykinin-induced tachyphylaxis, pleural exudation and leukocyte influx induced by antigen were drastically reduced, strongly implying bradykinin in this process. We demonstrated that repeated daily stimulation with bradykinin cause selective, local and reversible auto-refractoriness, which may be useful as a tool in attempting to evaluate the role of this peptide in inflammation.     

Melatonin reversal of lipopolysacharides-induced thermal and behavioral hyperalgesia in mice

The perception of pain sensation (threshold), whether local or central, is altered by inflammatory processes. Anti-inflammatory drugs block this by raising the pain threshold and by reducing the inflammatory process. Melatonin is claimed to have anti-inflammatory activity in animal models of acute and chronic inflammation. However, it is not known whether melatonin can reverse the hyperalgesia that is secondary to the inflammation. The present study aimed to assess the modulatory effect of melatonin on lipopolysaccharides-induced alteration of pain perception in mice. Central perception of pain was assessed with the tail-flick and hot-plate methods and local hyperalgesia was assessed by noting the animal's reactions such as paw licking and rearing after the intraplantar injection of lipopolysaccharides (5 microg/paw). Local administration (intraplantar) of lipopolysacharides induced hyperalgesia when measured by both central effects and behavioral reactions. Melatonin (5 and 10 mg/kg), like dexamethasone (0.5 mg/kg), given 30 min prior to, and 4 and 8 h after lipopolysaccharides (5 microg/paw) challenge attenuated central and behavioural hyperalgesia. The attenuation of lipopolysaccharides-induced hyperalgesia by melatonin was not reversed by naltrexone (4 mg/kg). In vitro studies showed that melatonin, in concentrations ranging from 100 to 1000 nM, suppressed tumor necrosis factor-alpha (TNF-alpha) without affecting the nitric oxide (NO) release in lipopolysaccharides-activated murine peritoneal macrophages. Taken together, the present results demonstrated that melatonin reverses lipopolysaccharides-induced hyperalgesia.     

Acute inflammatory response of the rat pawskin to acid injury is attenuated by corticotropin-releasing factor

Increased vascular permeability, as measured by changes in skin weight and Evans blue dye extravasation, was produced in the skin after immersion of the anesthetized rat's paw in 12 N hydrochloric, 18N sulfuric, or 14N hydrofluoric acids for 2 min. Corticotropin-releasing factor (CRF), a 41-residue peptide having the rat/human sequence, injected 28 micrograms/kg i.v. 10 min before immersion, was efficacious in reducing these indices of skin injury.     

Effects of cadmium in rat hepatocytes: interaction with aluminum

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic manganese-containing compound which is used as an additive in unleaded gasoline. One neurotoxic effect of MMT in mice is seizure activity. In this study, seizures were observed in mice treated with MMT in propylene glycol or corn oil. The LD50 associated with seizure activity was lower in mice receiving MMT in propylene glycol (152 mg/kg) than in those receiving MMT in corn oil (999 mg/kg). Manganese concentrations in the brains of mice which showed seizure activity due to MMT were higher than in those that did not (2.45 micrograms/g vs. 1.14 micrograms/g for MMT treated in propylene glycol and 3.25 micrograms/g vs. 1.63 micrograms/g for MMT in corn oil). Mice treated with manganese chloride (MnCl2) showed increases in brain manganese comparable to those of the mice showing seizure activity due to MMT, but exhibited no sign of seizure activity. MMT in non-lethal seizure-inducing doses had no effect on the accumulation of 4-aminobutyric acid (GABA) in mouse brain. However, MMT inhibited the binding of t-[3H]t-butylbicycloorthobenzoate [3H]-TBOB (a ligand for the GABA-A-receptor linked chloride channel) in mouse brain membranes with an IC50 value of 22.8 microM. The data suggest that MMT (organic manganese) or a closely related metabolite and not elemental manganese itself is responsible for the seizure activity observed. The seizure activity may be the result of an inhibitory effect of MMT at the GABA-A receptor linked chloride channel.     

Modulation of inflammatory paw oedema by cysteamine in the rat.

Cysteamine, a potent somatostatin depletor, was used in the present study to investigate the role of endogenous somatostatin in acute peripheral inflammation. The acute inflammation was induced by intraplantar injection of carrageenan (1%), histamine (5 micromol), or formalin (2.5%) in the rat hind paw. The induced inflammation and the formation of oedema were determined by measurement of the paw thickness. Given subcutaneously (s.c.) 1 h before carrageenan, cysteamine caused significant, dose-dependent and long-lasting inhibition of rat paw oedema induced by carrageenan. At doses of 12.5, 25, 50 or 100 mg kg (-1), cysteamine significantly inhibited the carrageenan-induced paw oedema at 4 h by 52.3, 40, 40.7 or 26.3%. Cysteamine given at 300 mg kg (-1), a dose well known to deplete tissue somatostatin, reduced oedema by only 16.2% vs control values. Significant inhibition of the carrageenan-induced rat paw oedema was still evident 24 h post-injection at cysteamine doses of 12.5, 25, 50 or 100 mg kg (-1). Given s.c. at 300 mg kg (-1), 4 h prior to carrageenan, cysteamine decreased rat paw oedema at 4 h by 14.9%. Cysteamine (300 mg kg (-1)), 4 h beforehand, had little modulatory effect on the oedema induced by formalin (2.5%) but reduced that caused by intraplantar histamine (5 micromol). The anti-oedematogenic effect of indomethacin, but not that of the selective COX-2 inhibitor celecoxib, was less marked in rats pre-treated with cysteamine at 300 mg kg (-1). Cysteamine (0.3 microg- 0.3 mg paw (-1)) co-administered with carrageenan was devoid of anti-inflammatory effect and even promoted inflammation at low concentrations. Cysteamine given locally alone induced slight paw oedema. These data indicate that systemic cysteamine possesses potent and long-lasting anti-inflammatory effects and modulates the anti-inflammatory effect of cyclooxygenase inhibitors in a model of peripheral inflammation in the rat. The effect of cysteamine is likely to be mediated via central action.     

Effect of topical administration of L-arginine on formalin-induced nociception in the mouse: a dual role of peripherally formed NO in pain modulation.

1. We investigated the effects of intraplantar (i.pl.) administration of L-arginine and NG-nitro-L-arginine methyl ester (L-NAME) on formalin-induced behavioural nociception in the mouse. 2. L- but not D-arginine, at 0.1-1 microgram per paw, coadministered with i.pl. formalin, enhanced the second-but not the first-phase nociceptive responses, whereas it was without significant effects at 3 micrograms per paw, and conversely, produced antinociception at 10 micrograms per paw, resulting in a bell-shaped dose-response curve. 3. L-NAME at 0.1-1 microgram per paw, when administered i.pl., exhibited antinociceptive activity in the second phase in a dose-dependent manner, although its D-enantiomer produced no effect. 4. An antinociceptive dose (1 microgram per paw) of L-NAME (i.pl.) considerably reduced the increase in second-phase nociception elicited by low doses (1 microgram per paw) of i.pl. L-arginine. The second-phase nociception decrease induced by a large dose (10 micrograms per paw) of i.pl. L-arginine was markedly reversed by i.pl. L-NAME at 0.1 micrograms per paw, raising it to a level above that of the control (formalin only). 5. These results suggest that peripheral NO plays a dual role in nociceptive modulation, depending on the tissue level, inducing either nociceptive or antinociceptive responses.     

Protective effect of melatonin in carrageenan-induced acute local inflammation.

The aim of the present study was to investigate the protective effect of the pineal hormone melatonin in a model of acute local inflammation (carrageenan-induced paw oedema). Inflammation was assessed by measurement of nitric oxide (NO), Malondialdehyde (MDA) and glutathione levels in the paw tissue in rats. The intraplantar injection of carrageenan elicited an inflammatory response that was characterised by a time-dependent increase in paw oedema, increased level of nitrite/nitrate and MDA, a lipid peroxidation product and decreased glutathione levels in the paw tissue. The maximal increase in paw volume was observed at 4h after administration (maximal in paw volume 160+/-3.34 ml). In addition, NO level and MDA were markedly increased in the carrageenan-treated paw (59.96+/-6.58 and 19.33+/-3.35 micromol g(-1), respectively), versus in the control paw glutathione level decreased in paw tissue (3.24+/-0.24 micromol g(-1)). However, carrageenan-induced paw oedema was significantly reduced in a dose-dependent manner by treatment with melatonin (given at 5 and 10 mg kg(-1)) at 1, 2, 3, 4, 5 and 6h after injection of carrageenan. Melatonin treatment also caused a significant reduction of the NO and MDA levels, while increasing glutathione level in the paw tissue. Our findings support the view that melatonin exerts anti-inflammatory effects. Part of these anti-inflammatory effect may be related to an inhibition of the NO and MDA production, while another part may be related to increase of the glutathione level in the paw tissue.     

Pharmacological evaluation of rat paw oedema induced by Bothrops jararaca venom

The mechanism involved in the genesis of the rat paw oedema caused by intraplantar (IPL) injection of Bothrops jararaca venom (BJV) has been investigated. IPL injection of BJV (1 to 30 micrograms/paw) caused a dose- and time-related oedematogenic effect. Oedema was maximal within 1 h after BJV injection, was partially reduced at 6 h and disappeared completely within 24 h. No systemic effect was observed. Previous heating of BJV at 100 degrees C for 3 to 30 min caused a significant inhibition (25%) of its oedematogenic activity. Daily IPL injections of BJV (10 micrograms/paw) for 4 days attenuated BJV-induced oedema (26%), but did not influence oedema-induced by PAF-acether, serotonin (5-HT) and histamine (His), indicating the absence of cross desensitization. In the paw desensitized by daily IPL injections of PAF-acether, BJV induced a full oedematogenic response also indicating absence of cross desensitization. Different groups of drugs including alpha 1- and alpha 2-adrenoceptor antagonists (prazosin and yohimbine), inhibitors of both cyclo- and lipo-oxygenase (indomethacin, nordihydroguaiaretic acid), inhibitors of phospholipase A2 (dexamethasone and mepacrine) caused marked inhibition of BJV-induced rat paw oedema, whereas antagonists of 5-HT, PAF-acether and H1-histamine receptors were less effective. Pre-treatment with a beta-adrenoceptor antagonist, a Ca2+ channel blocker and a H2-histamine antagonist failed to affect BJV-induced oedema. Pre-treatment of the animals with captopril did not interfere with BJV-induce oedema, suggesting that kinins are not insolved in the genesis of oedema. Association of BJV with 5-HT and PAF did not potentiate the BJV-induced oedema.(ABSTRACT TRUNCATED AT 250 WORDS)