Anti-allodynic effect of NW-1029, a novel Na(+) channel blocker,in experimental animal models of inflammatory and neuropathic pain

NW-1029, a benzylamino propanamide derivative, was selected among several molecules of this chemical class on the basis of its affinity for the [(3)H]batracotoxin ligand displacement of the Na(+) channel complex and also on the basis of its voltage and use-dependent inhibitory action on the Na(+) currents of the rat DRG (dorsal root ganglia) sensory neuron. This study evaluated the analgesic activity of NW-1029 in animal models of inflammatory and neuropathic pain (formalin test in mice, complete Freund's adjuvant and chronic constriction injury in rats) as well as in acute pain test (hot-plate and tail-flick in rats). Orally administered NW-1029 dose-dependently reduced cumulative licking time in the early and late phase of the formalin test (ED(50)=10.1 mg/kg in the late phase). In the CFA model, NW-1029 reversed mechanical allodynia (von Frey test) after both i.p. and p.o. administration (ED(50)=0.57 and 0.53 mg/kg), respectively. Similarly, NW-1029 reversed mechanical allodynia in the CCI model after both i.p. and p.o. administration yielding an ED(50) of 0.89 and 0.67 mg/kg, respectively. No effects were observed in the hot-plate and tail-flick tests up to 30 mg/kg p.o. The compound orally administered (0.1-10 mg/kg) was well tolerated, without signs of neurological impairment up to high doses (ED(50)=470 and 245 mg/kg in rat and mice Rotarod test, respectively). These results indicate that NW-1029 has anti-nociceptive properties in models of inflammatory and neuropathic pain.     

Role of the nitric-oxide synthase isoforms during morphine-induced hyperthermia in rats

Recently, we demonstrated that the diffusible messenger molecule nitric oxide (NO) is involved in the hyperthermic response induced by morphine by using a nonselective nitric-oxide synthase inhibitor, N-nitro-L-arginine methyl ester. The present work extended these studies to include 7-nitroindazole (7-NI), an inhibitor specific for neuronal nitric-oxide synthase (nNOS), N(5)-(-iminoethyl)-L-ornithine (L-NIO), an inhibitor of endothelial NOS (eNOS), and aminoguanidine (AG), a potent inhibitor of inducible NOS (iNOS). A biotelemetry system was used in this study to measure the body temperature (Tb). A dose of 7-NI (5 or 10 mg/kg), which did not affect Tb by itself, blocked the hyperthermia induced by morphine in a dose-dependent manner (15 mg/kg i.p.). However, pretreatment with L-NIO (10-20 mg/kg) or with AG (50 mg/kg) failed to alter the hyperthermia induced by morphine. L-NIO (10-20 mg/kg) or AG (50 mg/kg) had no effect on Tb. These results suggest the involvement of nNOS in morphine-induced hyperthermia.     

Gabapentin and pregabalin, but not morphine and amitriptyline, block both static and dynamic components of mechanical allodynia induced by streptozocin in the rat

A single injection of streptozocin (50 mg/kg, i.p.) led to the development of static and dynamic allodynia in the rat. The two responses were detected, respectively, by application of pressure using von Frey hairs or lightly stroking the hind paw with a cotton bud. Static allodynia was present in the majority of the animals within 10 days following streptozocin. In contrast, dynamic allodynia took almost twice as long to develop and was only present in approximately 60% of rats. Morphine (1-3 mg/kg, s.c.) and amitriptyline (0.25-2.0 mg/kg, p.o.) dose-dependently blocked static allodynia. However, neither of the compounds was effective against dynamic allodynia. In contrast, gabapentin (10-100 mg/kg, p.o.) and the related compound pregabalin (3-30 mg/kg, p.o.) dose-dependently blocked both types of allodynia. However, the corresponding R-enantiomer (10-100 mg/kg, p.o.) of pregabalin, was found to be inactive. The intrathecal administration of gabapentin dose-dependently (1-100 microg/animal) blocked both static and dynamic allodynia. In contrast, administration of similar doses of gabapentin into the hind paw failed to block these responses. It is suggested that in this model of neuropathic pain dynamic allodynia is mediated by A beta-fibres and the static type involves small diameter nociceptive fibres. These data suggest that gabapentin and pregabalin possess a superior antiallodynic profile than morphine and amitriptyline, and may represent a novel class of therapeutic agents for the treatment of neuropathic pain.     

Antinociceptive activity of the selective iNOS inhibitor AR-C102222 in rodent models of inflammatory, neuropathic and post-operative pain.

Nitric oxide generated by the nitric oxide synthase (NOS) isoforms contributes to pain processing. The selective inhibition of iNOS might represent a novel, therapeutic target for the development of antinociceptive compounds. However, few isoform-selective inhibitors of NOS have been developed. The present experiments examined the anti-inflammatory and antinociceptive activity of a selective inducible nitric oxide (iNOS) inhibitor, AR-C102222, on arachidonic acid-induced ear inflammation, Freund's complete adjuvant (FCA)-induced hyperalgesia, acetic acid-induced writhing, and tactile allodynia produced by L5 spinal nerve ligation (L5 SNL) or hindpaw incision (INC). AR-C102222 at a dose of 100mg/kg p.o., significantly reduced inflammation produced by the application of arachidonic acid to the ear, attenuated FCA-induced mechanical hyperalgesia, and attenuated acetic acid-induced writhing. In the L5 SNL and INC surgical procedures, tactile allodynia produced by both procedures was significantly reduced by 30mg/kg i.p. of AR-C102222. These data demonstrate that the selective inhibition of iNOS produces antinociception in different models of pain and suggest that the iNOS-NO system plays a role in pain processing.     

Pharmacological characterization of lysophosphatidic acid‐induced pain with clinically relevant neuropathic pain drugs

Lysophosphatidic acid (LPA), an initiator of neuropathic pain, causes allodynia. However, few studies have evaluated the pharmacological profile of LPA‐induced pain. In this study, a LPA‐induced pain model was developed and pharmacologically characterized with clinically relevant drugs used for neuropathic pain, including antiepileptics, non‐steroidal anti‐inflammatory agents, analgesics, local anaesthetics/antiarrhythmics and antidepressants. Gabapentin (1–30 mg/kg, p.o.) significantly reversed LPA‐induced allodynia, but neither indomethacin (30 mg/kg, p.o.) nor morphine (0.3–3 mg/kg, s.c.) did, which indicates that LPA‐induced pain consists mostly of neuropathic rather than inflammatory pain. Both pregabalin (0.3–10 mg/kg, p.o.) and ω‐CgTX MVIIA (0.01–0.03 μg/mouse, i.t.) completely reversed LPA‐induced allodynia in a dose‐dependent manner. Lidocaine (1–30 mg/kg, s.c.), mexiletine (1–30 mg/kg, p.o.) and carbamazepine (10–100 mg/kg, p.o.) significantly ameliorated LPA‐induced allodynia dose dependently. Milnacipran (30 mg/kg, i.p.) produced no significant analgesic effect in LPA‐induced allodynia. In LPA‐injected mice, expression of the α2δ1 subunit of the voltage‐gated calcium channel (VGCC) was increased in the dorsal root ganglion (DRG) and spinal dorsal horn. Furthermore, the VGCC current was potentiated in both the DRG from LPA‐injected mice and LPA (1 μM)‐treated DRG from saline‐injected mice, and the potentiated VGCC current was amended by treatment with gabapentin (100 μM). The LPA‐induced pain model described here mimics aspects of the neuropathic pain state, including the sensitization of VGCC, and may be useful for the early assessment of drug candidates to treat neuropathic pain.     

The cyclooxygenase-2 inhibitor GW406381X [2-(4-ethoxyphenyl)-3-[4-(methylsulfonyl)phenyl]-pyrazolo[1,5-b]pyridazine] is effective in animal models of neuropathic pain and central sensitization

The pathogenic form of the cyclooxygenase (COX) enzyme, COX-2, is also constitutively present in the spinal cord and has been implicated in chronic pain states in rat and man. A number of COX-2 inhibitors, including celecoxib and rofecoxib, are already used in man for the treatment of inflammatory pain. Preclinically, the dual-acting COX-2 inhibitor, GW406381X [2-(4-ethoxyphenyl)-3-[4-(methylsulfonyl)phenyl]-pyrazolo[1,5-b]pyridazine, where X denotes the free base], is as effective as rofecoxib and celecoxib in the rat established Freund's Complete Adjuvant model with an ED(50) of 1.5 mg/kg p.o. compared with 1.0 mg/kg p.o. for rofecoxib and 6.6 mg/kg p.o. for celecoxib. However, in contrast to celecoxib (5 mg/kg p.o. b.i.d.) and rofecoxib (5 mg/kg p.o. b.i.d.), which were without significant effect, GW406381X (5 mg/kg p.o. b.i.d.) fully reversed mechanical allodynia in the chronic constriction injury model and reversed thermal hyperalgesia in the mouse partial ligation model, both models of neuropathic pain. GW406381X, was also effective in a rat model of capsaicin-induced central sensitization, when given intrathecally (ED(50) = 0.07 mug) and after chronic but not acute oral dosing. Celecoxib and rofecoxib had no effect in this model. Several hypotheses have been proposed to try to explain these differences in efficacy, including central nervous system penetration, enzyme kinetics, and potency. The novel finding of effectiveness of GW406381X in these models of neuropathic pain/central sensitization, in addition to activity in inflammatory pain models and together with its central efficacy, suggests dual activity of GW406381X compared with celecoxib and rofecoxib, which may translate into greater efficacy in a broader spectrum of pain states in the clinic.     

Antinociceptive activity of the N-methyl-D-aspartate receptor antagonist N-(2-Indanyl)-glycinamide hydrochloride (CHF3381) in experimental models of inflammatory and neuropathic pain

N-(2-Indanyl)-glycinamide hydrochloride (CHF3381) is a novel low-affinity, noncompetitive N-methyl-d-aspartate receptor antagonist. The current study compared the antinociceptive effects of CHF3381 with those of gabapentin and memantine in in vitro and in vivo models of pain. In isolated rat spinal cord, CHF3381 and memantine, but not gabapentin, produced similar inhibition of the wind-up phenomenon. CHF3381 suppressed the maintenance of carrageenan-induced thermal and mechanical hyperalgesia in the rat with a minimum significantly effective dose (MED) of 30 mg/kg p.o. Memantine produced a partial reversal of both thermal and mechanical hyperalgesia (MED = 10 and 15 mg/kg i.p., respectively). Gabapentin reversed mechanical hyperalgesia (MED = 10 mg/kg s.c.), but did not affect thermal hyperalgesia. In the mouse formalin test, CHF3381 and memantine preferentially inhibited the late phase (MED = 30 and 20 mg/kg i.p., respectively); gabapentin inhibited only the late phase (MED = 30 mg/kg s.c.). Unlike morphine, CHF3381 chronic administration was not accompanied by the development of tolerance in the formalin test. Furthermore, morphine tolerance did not cross-generalize to CHF3381. In rats with a sciatic nerve injury, CHF3381 relieved both cold and mechanical allodynia (MED = 100 mg/kg p.o.). In contrast, memantine was inactive. Gabapentin blocked cold allodynia (MED = 30 mg/kg s.c.), but had marginal effects on mechanical allodynia. In diabetic neuropathy, CHF3381 reversed mechanical hyperalgesia (MED = 50 mg/kg p.o.). Memantine (15 mg/kg i.p.) produced an antinociceptive effect, whereas gabapentin (100 mg/kg p.o.) had no significant effect. Thus, CHF3381 may be useful for the therapy of peripheral painful neuropathies.     

Evidence that CB-1 and CB-2 cannabinoid receptors mediate antinociception in neuropathic pain in the rat

The roles of the two cannabinoid receptor subtypes, CB-1 and CB-2, have not been clarified in cannabinoid-mediated analgesia. We investigated the efficacy of the non-selective cannabinoid receptor agonist CP55,940 in the modulation of responses in the rat to both acute pain (tail flick) and neuropathic pain (tactile allodynia following chronic L5/6 spinal nerve ligation). Responses were also assessed in the presence of the CB-1 antagonist SR141716A (SR1) and the CB-2 antagonist SR144528 (SR2). CP55,940 attenuated tactile allodynia (ED(50) 0.04 mg/kg i.t. (95% CI 0.032-0.044 mg/kg), 0.12 mg/kg i.p. (95% CI 0.10-0.15 mg/kg)) and induced thermal antinociception (ED(50) tail flick 0.07 mg/kg i.t. (95% CI 0.05-0.10 mg/kg), 0.17 mg/kg i.p. (95% CI 0.11-0.26 mg/kg)). SR1 0.5 mg/kg i.t. attenuated the antinociceptive effect of CP55,940 in both modalities. However, SR1 1.0 mg/kg i.p. decreased tail flick latency but had no effect on tactile allodynia antinociception. In contrast, SR2 1.0 mg/kg i.p. significantly decreased the effect of i.p. CP55,940 on both tail flick antinociception and tactile allodynia (P<0.005). The combination of SR1 and SR2 (i.p.) had an additive effect in decreasing the antinociception induced by CP55,940 on tail flick responses (P<0.005). These results suggest a role for CB-2 receptor-mediated antinociception in both acute and neuropathic pain in addition to centrally located CB-1 mechanisms.     

Attenuation of mechanical allodynia by clinically utilized drugs in a rat chemotherapy-induced neuropathic pain model

Chemotherapy-induced peripheral neuropathy is a common, dose-limiting side effect of cancer chemotherapeutic agents, including the vinca alkaloids such as vincristine. The resulting symptoms, which frequently include moderate to severe pain, can often be disabling. The current study utilized a vincristine-induced neuropathic pain animal model [Pain 93 (2001) 69], in which rats were surgically implanted with mini-osmotic pumps set to deliver vincristine sulfate (30 microg kg(-1)day(-1), i.v.), to examine the time course of progression of various pain modalities and to compare the dose-response effects of clinically utilized drugs on mechanical allodynia to further validate the relevance of this model to clinical pathology. Vincristine infusion resulted in significant cold allodynia after 1 week post-infusion, however mechanical and thermal nociception showed little to no effect. In contrast, marked mechanical allodynia occurred by 1 week of vincristine infusion and returned nearly to pre-infusion levels by the 4th week after infusion pump implantation. ED(50) values (micromol/kg, p.o.) were determined in the mechanical allodynia assay for lamotrigine (82), dextromethorphan (94), gabapentin (400), acetaminophen (1100) and carbamazepine (3600); however, aspirin and ibuprofen had no effects up to 300 and 1000 micromol/kg, respectively. Additionally, ED(50) values (micromol/kg, i.p.) were determined in the mechanical allodynia assay for clonidine (0.35) and morphine (0.62), but desipramine and celecoxib had no effects up to 66 and 260 micromol/kg, respectively. Findings from the current, preclinical study further validate this model as clinically relevant for chemotherapy-induced pain. The surprisingly good effects observed with acetaminophen warrant further investigation of its mechanism(s) of action in neuropathic pain.     

Gabapentin antinociception in mice with acute herpetic pain induced by herpes simplex virus infection

The effects of systemic and local injections of gabapentin, a novel anticonvulsant agent, were tested on nociceptive behaviors in mice with acute herpetic pain. Transdermal infection with herpes simplex virus type-1 (HSV-1) produced nociceptive hypersensitivity of the infected hind paw to innocuous (allodynia) and noxious mechanical stimulation (hyperalgesia) with von Frey filaments. Systemic administration of gabapentin (10-100 mg/kg, peroral) produced a dose-dependent inhibition of both allodynia and hyperalgesia; gabapentin (30-300 mg/kg) did not affect locomotor activity. Intrathecal injection of gabapentin (10-100 microg/animal) also attenuated dose dependently both nociceptive hypersensitivities. In contrast, intraplantar, intracisternal, and intracerebroventricular administration of gabapentin (10-100 microg/animal) had no effect on the HSV-1-induced nociceptive hypersensitivities. Pretreatment with naltrexone (1 mg/kg) inhibited antinociceptive effect of morphine (5 mg/kg), but not gabapentin (100 mg/kg). Repeated administration of morphine (5 mg/kg, four times) led to tolerance of antinociceptive action, whereas gabapentin (100 mg/kg, four times) had antinociceptive effect even after the forth administration. The present results suggest that gabapentin is effective in the treatment of acute herpetic pain without apparent adverse effects, and analgesic action of gabapentin is mainly mediated by actions on the spinal cord.     

Pemedolac: a novel and long-acting non-narcotic analgesic

Pemedolac [cis-1-ethyl-1,3,4,9-tetrahydro-4-(phenylmethyl)-pyrano [3,4-b]indole-1-acetic acid; AY-30,715] exhibited potent analgesic effects against chemically induced pain in rats and mice and against inflammatory pain in rats. In each of the animal models used the analgesic potency of pemedolac was defined by an ED50 of 2.0 mg/kg p.o. or less. Significant analgesic activity was detected in rats at 16 hr after administration of 1 mg/kg p.o. (paw pressure test) and at 10 hr after administration of 10 mg/kg p.o. to mice (p-phenylbenzoquinone writhing). Inasmuch as pemedolac was inactive in the hot plate and tail-flick tests; and its analgesic activity was not antagonized by naloxone (1 mg/kg s.c.), and tolerance did not develop upon multiple administration; this drug does not exert its analgesic effects through an opiate mechanism. Pemedolac differed from standard nonsteroidal anti-inflammatory drugs (NSAIDs) in that the doses which produced analgesia were much lower than those required for either anti-inflammatory or gastric irritant effects. In acute anti-inflammatory tests, pemedolac exhibited only weak activity as evidenced by an ED50 approximately 100 mg/kg p.o. in the carrageenan paw edema procedure. This demonstrates for pemedolac a separation of at least 50-fold between the acute analgesic and anti-inflammatory activities, which was greater than that observed with reference NSAIDs. The compound also had a low ulcerogenic liability with an acute UD50 = 107 mg/kg p.o. and a subacute UD50 estimated to be 140 mg/kg/day p.o. In contrast, the reference NSAIDS (piroxicam, indomethacin, naproxen and ibuprofen) exhibited similar dose-response relationships for the analgesic, anti-inflammatory and gastric irritant effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of 2-[N-(4-chlorophenyl)-N-methylamino]-4H-pyrido[3.2-e]-1,3-thiazin-4-one (YM928), an orally active alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist, in models of generalized epileptic seizure in mice and rats

The anticonvulsant activity of 2-[N-(4-chlorophenyl)-N-methylamino]-4H-pyrido[3.2-e]-1,3-thiazin-4-one (YM928), a novel alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, was studied in animal models of generalized seizure. YM928 exerted significant anticonvulsant effects in the maximal electroshock (MES) seizure test (ED50 = 7.4 mg/kg p.o.), pentylenetetrazol (PTZ)-induced seizure test (ED50 = 9.6 mg/kg p.o.), AMPA-induced seizure test (ED50 = 5.5 mg/kg p.o.), and strychnine-induced seizure test (ED50 = 14.0 mg/kg p.o.) in mice. Effects in rats were detected in the MES seizure test (ED50 = 4.0 mg/kg p.o.) and PTZ-induced seizure test (ED50 = 6.2 mg/kg p.o.). The profile of YM928 was compared with that of established antiepileptics. Valproate showed beneficial effects in all tests used. In contrast, carbamazepine, phenytoin, lamotrigine, phenobarbital, diazepam, ethosuximide, and gabapentin were not active against seizures induced by at least one stimulant. In the rotarod test, YM928 impaired motor coordination (TD50 = 22.5 mg/kg p.o.). The protective index (TD50 value of the rotarod test/ED50 value of MES seizure) was 3.0, suggesting that YM928 can exert antiepileptic effects with only minor motor disturbances. YM928 at doses of 2, 4, and 8 mg/kg p.o. did not significantly affect the threshold of electroshock seizure in rats after 16 days of repeated administration. These data indicate that YM928 does not induce tolerance after subchronic administration. These results indicate that YM928 is a broad-spectrum anticonvulsant that would prove useful for the treatment of generalized seizure in human epileptic patients.     

In vivo characterization of the novel imidazopyridine BYK191023 [2-[2-(4-methoxy-pyridin-2-yl)-ethyl]-3H-imidazo[4,5-b]pyridine], a potent and highly selective inhibitor of inducible nitric-oxide synthase

Excessive release of nitric oxide from inducible nitric-oxide synthase (iNOS) has been postulated to contribute to pathology in a number of inflammatory diseases. We recently identified imidazopyridine derivatives as a novel class of potent nitricoxide synthase inhibitors with high selectivity for the inducible isoform. In the present study, we tested the in vivo potency of BYK191023 [2-[2-(4-methoxy-pyridin-2-yl)-ethyl]-3H-imidazo-[4,5-b]pyridine], a selected member of this inhibitor class, in three different rat models of lipopolysaccharide-induced systemic inflammation. Delayed administration of BYK191023 dose-dependently suppressed the lipopolysaccharide-induced increase in plasma nitrate/nitrite (NO(x)) levels with an ED(50) of 14.9 micromol/kg/h. In a model of systemic hypotension following high-dose lipopolysaccharide challenge, curative administration of BYK191023 at a dose that inhibited 83% of the NO(x) increase completely prevented the gradual decrease in mean arterial blood pressure observed in vehicle-treated control animals. The vasopressor effect was specific for endotoxemic animals since BYK191023 did not affect blood pressure in saline-challenged controls. In addition, in a model of lipopolysaccharide-induced vascular hyporesponsiveness, BYK191023 infusion partially restored normal blood pressure responses to norepinephrine and sodium nitroprusside via an l-arginine competitive mechanism. Taken together, BYK191023 is a member of a novel class of highly isoform-selective iNOS inhibitors with promising in vivo activity suitable for mechanistic studies on the role of selective iNOS inhibition as well as clinical development.     

Characterization of the acute and persistent pain state present in K/BxN serum transfer arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune arthritis that affects approximately 1% of the population. Synovial inflammation cannot fully explain the level of pain reported by patients and facilitation of pain processing at the spinal level has been implicated. We characterized the K/BxN serum transfer arthritis model as a model of joint inflammation-induced pain and examined pharmacologic responsiveness and spinal glia activation. Mechanical allodynia developed congruently with joint swelling. Surprisingly, allodynia persisted after resolution of inflammation. At the peak of joint inflammation (days 4-10), hypersensitivity was attenuated with i.p. etanercept, gabapentin, and ketorolac. Following resolution of synovial inflammation (days 19-23), only gabapentin relieved allodynia. The superficial dorsal horn of arthritic mice displayed increased staining of microglia at early and late time points, but astrocyte staining increased only during the inflammatory phase. ATF3, a marker of nerve injury, was significantly increased in the lumbar dorsal root ganglia during the late phase (day 28). Hence, serum transfer in the K/BxN serum transfer arthritis model produces a persistent pain state, where the allodynia during the inflammatory state is attenuated by TNF and prostaglandin inhibitors, and the pharmacology and histochemistry data suggest a transition from an inflammatory state to a state that resembles a neuropathic condition over time. Therefore, the K/BxN serum transfer model represents a multifaceted model for studies exploring pain mechanisms in conditions of joint inflammation and may serve as a platform for exploring novel treatment strategies for pain in human arthritic conditions.     

Pharmacology of pravadoline: a new analgesic agent

Pravadoline is a new chemical entity with analgesic activity in humans. This report describes the pharmacology of pravadoline and compares the activity of pravadoline with that of two major classes of analgesics, the opioids and the nonsteroidal anti-inflammatory drugs (NSAIDs). Like the NSAIDs, pravadoline inhibited the synthesis of prostaglandins (PGs) in mouse brain both in vitro (IC50, 4.9 microM) and ex vivo (ED50, 20 mg/kg p.o.) and displayed antinociceptive activity in rodents subjected to a variety of chemical, thermal and mechanical nociceptive stimuli. Administration of pravadoline prevented the writhing response induced by i.p. administration of acetylcholine (ED50, 41 mg/kg p.o.) or PGE2 (ED50, 24 mg/kg p.o.) and prolonged the response latency induced by tail immersion in hot water at a temperature of 55 degrees C (minimum effective dose, 100 mg/kg s.c.). In the rat, treatment with pravadoline prevented acetic acid-induced writhing (ED50, 15 mg/kg p.o.), brewer's yeast-induced hyperalgesia (Randall-Selitto test) (minimum effective dose, 1 mg/kg p.o.), the nociceptive response induced by paw flexion in the adjuvant-arthritic rat (ED50, 41 mg/kg p.o.) and bradykinin-induced head and forepaw flexion (ED50, 78 mg/kg, p.o.). The antinociceptive activity of pravadoline cannot be explained by an opioid mechanism, because pravadoline-induced antinociception was not antagonized by naloxone (1 mg/kg s.c.) and pravadoline did not bind to opioid receptors at concentrations up to 10 microM. However, like the opioid analgesics, pravadoline diminished the electrically induced twitch response of mouse vas deferens preparations, but, in contrast to opioids, this action of pravadoline was not attenuated by naloxone. The possibility is discussed that this effect of pravadoline upon isolated tissues may contribute to its antinociceptive activity. In contrast to NSAIDs, pravadoline was more potent ex vivo as an inhibitor of the formation of PGs in brain vs. stomach. In addition, pravadoline failed to produce gastrointestinal lesions when administered p.o. to rats or mice, and did not possess significant anti-inflammatory activity at antinociceptive doses. Also unlike NSAIDs, pravadoline inhibited rat gastrointestinal transit when administered at doses similar to those which were antinociceptive. The overall pharmacologic profile of pravadoline suggests that the compound may be capable of managing more diverse or more severe pain than is achieved by anti-inflammatory analgesics, without producing side effects commonly associated with either the opioid or the nonopioid analgesics.     

7-nitroindazole, but not L-NAME or aminoguanidine, attenuates anaphylactic hypotension in conscious rats

The roles of NO and isozymes of NO synthase (NOS) are not known in anaphylactic hypotension of unanesthetized rats. Effects of inhibition of NOS, iNOS, and nNOS by N-nitro-L-arginine methyl ester (L-NAME), aminoguanidine, and 7-nitroindazole, respectively, were determined on the antigen-induced systemic hypotension and portal hypertension in conscious Sprague-Dawley rats sensitized with the ovalbumin antigen. The MAP and portal venous pressure were directly and simultaneously measured. The control rats showed a decrease in MAP along with an increase in portal venous pressure but did not die within 48 h after antigen injection. In the rats pretreated with the nonselective NOS inhibitor L-NAME (10 mg/kg), MAP before and after antigen administration was significantly higher than that of the control rats, but the net decrease in MAP and increase in portal venous pressure were rather greater than those of the control, resulting in fatal outcome within 12 h after antigen administration. In contrast, pretreatment with the relatively selective nNOS inhibitor 7-nitroindazole (50 mg/kg) substantially attenuated anaphylactic hypotension over 20 min after antigen administration, whereas the relatively selective iNOS inhibitor aminoguanidine (100 mg/kg) did not affect it. In conclusion, in anaphylactic hypotension of unanesthetized rats, NO derived from nNOS, but not from iNOS, may be involved, and the nonselective NOS inhibitor L-NAME is lethal.     

Suppression of acute experimental colitis by a highly selective inducible nitric-oxide synthase inhibitor, N-[3-(aminomethyl)benzyl]acetamidine

High concentrations of nitric oxide (NO) produced by the inducible nitric-oxide synthase (iNOS) are associated with ulcerative inflammation and disease activity in colitis. Therefore, inhibition of iNOS serves as a novel experimental approach to treat gut inflammation. The aim of the present study was to investigate the effects of a novel highly selective iNOS inhibitor, N-[3-(aminomethyl)benzyl]acetamidine (1400W), as compared with a nonselective NOS inhibitor, N(G)-nitro-L-arginine-methyl-ester (L-NAME), in 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced acute colitis in the rat. Increased expression of iNOS protein and mRNA was found in acute TNBS-induced colitis along with neutrophil infiltration, inflammatory edema, and tissue damage. In a 24-h model of acute colitis, subcutaneous injections of 1400W (5 or 10 mg/kg t.i.d.) produced a 56 and 95% reduction in inflammatory edema formation, a 68 and 63% reduction in neutrophil infiltration (measured as myeloperoxidase activity), and a 19 and 26% decrease in the size of mucosal lesions as compared with vehicle treatment. Administration of L-NAME (35 mg/kg) failed to produce any significant beneficial effects as compared with vehicle treatment in this experimental model of acute colitis. Treatment with 1400W, a highly selective inhibitor of iNOS, reduced formation of edema, neutrophil infiltration, and macroscopic inflammatory damage in experimentally induced acute colitis in the rat. In contrast, nonselective nitric-oxide synthase inhibition with L-NAME provided no benefit. These results support the idea that selective iNOS inhibitors have a promise in the treatment of colitis.     

Effects of ORF 17583, other histamine H2-receptor antagonists and omeprazole on gastric acid secretory states in rats and dogs

ORF 17583, a histamine H2-receptor antagonist, inhibited gastric acid secretion in pylorus-ligated rats (ED50 = 4.9 mg/kg intraduodenal; 3.4 mg/kg p.o.; and 0.21 mg/kg i.p.) and in total gastric fistula or Heidenhain pouch dogs stimulated by betazole (ED50 = 0.12 mg/kg p.o. and 0.08 mg/kg i.v.), histamine, tetragastrin, bethanechol, 2-deoxy-D-glucose or a meal (ED50 values ranged from 0.11-0.26 mg/kg p.o.). The nonspecific inhibition of gastric acid by ORF 17583 supports the existence of interdependence between histamine and the gastrin and cholinergic receptors on the parietal cell surface. Antisecretory potency of ORF 17583 after intraduodenal administration in pylorus-ligated rats was 6.4 times greater than cimetidine, 1.8 times greater than ranitidine, equal to that of omeprazole and 8 times less than that of famotidine. Oral antisecretory potency of ORF 17583 in gastric fistula dogs was 31 times greater than cimetidine, 3.7 times greater than ranitidine and equal to that of omeprazole and famotidine. Studies using equieffective antisecretory doses of ORF 17583 and ranitidine in dogs suggested that ORF 17583 has a short duration of antisecretory activity similar to that of ranitidine.     

Suppression of acute herpetic pain-related responses by the kappa-opioid receptor agonist (-)-17-cyclopropylmethyl-3,14beta-dihydroxy-4,5alpha-epoxy-beta-[n-methyl-3-trans-3-(3-furyl) acrylamido] morphinan hydrochloride (TRK-820) in mice

(-)-17-Cyclopropylmethyl-3,14beta-dihydroxy-4,5alpha-epoxy-6beta-[N-methyl-3-trans-3-(3-furyl) acrylamido] morphinan hydrochloride (TRK-820) is a kappa-opioid receptor agonist that has pharmacological characteristics different from typical kappa-opioid receptor agonists. This study was conducted to determine the antiallodynic and antihyperalgesic effects of TRK-820 in a mouse model of acute herpetic pain and to compare them with those of the kappa-opioid receptor agonist enadoline and the mu-opioid receptor agonist morphine. Percutaneous inoculation with herpes simplex virus type-1 induced tactile allodynia and mechanical hyperalgesia in the hind paw on the inoculated side. TRK-820 (0.01-0.1 mg/kg p.o.), enadoline (1-10 mg/kg p.o.) and morphine (5-20 mg/kg p.o.) dose dependently inhibited the allodynia and hyperalgesia, but the antiallodynic and antihyperalgesic dose of enadoline markedly decreased spontaneous locomotor activity. The antinociceptive action of TRK-820 (0.1 mg/kg) was completely antagonized by pretreatment with norbinaltorphimine, a kappa-opioid receptor antagonist, but not by naltrexone, a mu-opioid receptor antagonist. Repeated treatment with morphine (20 mg/kg, four times) resulted in the reduction of antiallodynic and antihyperalgesic effects, whereas the inhibitory potency of TRK-820 (0.1 mg/kg) was almost the same even after the fourth administration. There was no cross-tolerance in antinociceptive activities between TRK-820 and morphine. Intrathecal and intracerebroventricular, but not intraplantar, injections of TRK-820 (10-100 ng/site) suppressed the allodynia and hyperalgesia. These results suggest that TRK-820 inhibits acute herpetic pain through kappa-opioid receptors in the spinal and supraspinal levels. TRK-820 may have clinical efficacy in acute herpetic pain with enough safety margins.