A new model to assess analgesic activity: Pain-induced functional impairment in the rat (PIFIR)

Quercetin decreases the antinociceptive effect of diclofenac in an arthritic gout-pain model in rats

OBJECTIVE

To analyse the antinociceptive interaction between quercetin (QUER) and diclofenac (DIC) in experimental arthritic gout-pain.

METHODS

The antinociceptive effect of DIC and QUER alone and in combination were evaluated using an arthritic gout-pain model. Pain was induced through intra-articular administration of uric acid in the rats and the treatments were administered 2 h later. Additionally, the cyclooxygenase (COX) activity was determined in rats treated with DIC, QUER and their combination.

KEY FINDINGS

DIC induced a maximal effect of 69.7 ± 2.7% with 3.1 mg/kg; whereas QUER only produced 17.6 ± 2.6% with the maximal dose (316 mg/kg). Ten of twelve DIC + QUER combinations showed a lesser antinociceptive effect than DIC alone did (P < 0.05). Moreover, DIC reduced total-COX (70.4 ± 1.3 versus 52.4 ± 1.8 and 77.4 ± 9.0 versus 56.1 ± 1.3, P < 0.05) and COX-2 (60.1 ± 1.0 versus 42.4 ± 1.8 and 58.1 ± 2.4 versus 48.7 ± 1.3, P < 0.05) activity after 1 and 3 h, respectively. Nevertheless, only the COX-2 activity induced by DIC was prevented in the presence of QUER (63.2 ± 3.0 versus 60.1 ± 1.0 and 56.6 ± 1.3 versus 58.1 ± 2.4 at 1 and 3 h, respectively).

CONCLUSIONS

All these data demonstrated that the simultaneous administration of QUER + DIC produces an unfavorable interaction on the antinociceptive effect of DIC. Therefore, this combination might not be recommendable to relieve arthritic gout-pain.

Pharmacokinetics and Pharmacodynamics of (S)-Ketoprofen Co-Administered with Caffeine: A Preclinical Study in Arthritic Rats

The purpose of the present study was to determine whether caffeine modifies the pharmacokinetics and pharmacodynamics of (S)-ketoprofen following oral administration in a gout-type pain model. 3.2 mg/kg of (S)-ketoprofen alone and combined with 17.8 mg/kg of caffeine were administered to Wistar rats and plasma levels were determined between 0.5 and 24.0 h. Additionally, antinociception was evaluated based on the protocol of the PIFIR (pain-induced functional impairment in the rat) model before blood sampling between 0.5 and 4.0 h. Significant differences in C_max, AUC_0-24, and AUC_0-∞ values were observed with caffeine administration (p < 0.05). Also, significant differences in E_max, T_max, and AUC_0-4 values were determined when comparing the treatments with and without caffeine (p < 0.05). By relating the pharmacokinetic and pharmacodynamic data, a counter-clockwise hysteresis loop was observed regardless of the administration of caffeine. When the relationship between AUCe and AUCp was fitted to the sigmoidal E_max model, a satisfactory correlation was found (R² > 0.99) as well as significant differences in E_max and EC₅₀ values (p < 0.05). With caffeine, E_max and EC₅₀ values changed by 489.5% and 695.4%, respectively. The combination studied represents a convenient alternative for the treatment of pain when considering the advantages offered by using drugs with different mechanisms of action.

Pharmacokinetics and pharmacodynamics of metamizol in co-administration with morphine under acute and chronic treatments in arthritic rats

Objective

To investigate the relationship between metamizol pharmacokinetics and the antinociceptive effect produced after subcutaneous administration of metamizol (177.8 mg/kg) alone or in combination with morphine (3.2 mg/kg), under acute and chronic treatments.

Methods

Antinociception was assessed using the pain-induced functional impairment model in rat (PIFIR). Serial blood samples were collected from the same animals to study the pharmacokinetics of metamizol.

Key findings

The co-administration of the drugs in single dose, confirmed the potentiation of their individual antinociceptive effects. When the drugs were administered alone following the chronic schedule, a pronounced tolerance development to their antinociceptive effects was found, whereas it was significantly attenuated when they were administered together. Metamizol pharmacokinetics was unaltered by the presence of morphine. Plasma concentrations of 4-methylaminoantipyrine, an active metabolite markedly decreased under chronic administration.

Conclusions

The mechanism involved in the potentiation of the antinociceptive effect produced by the combination, cannot be explained by the interaction of morphine on metamizol pharmacokinetics. Other pharmacokinetic interactions along with known pharmacodynamic interactions in which metamizol active metabolites contribute, should be considered. The frequency of administration enhances tolerance development and induces metamizol elimination process.

Nociceptive Alteration by High Sucrose Diet in Hypoestrogenic Wistar Rats

Preclinical Research Obesity is a risk factor associated with alterations in pain perception. The aim of this study was to analyse a time-course of nociceptive responses (plantar test) in hypoestrogenic rats after the induction of obesity. Animals (hypoestrogenic and naïve) received either a hypercaloric or regular diet for 24 weeks. Thermal nociception and body weight were measured during this period. At the 4th and 17th weeks after treatment, oral glucose tolerance, blood insulin levels, abdominal fat weight, and uric acid levels were measured. The hypoestrogenic rats on a high sucrose diet had higher body weight and abdominal fat weight than control rats. A biphasic response was observed in the ovariectomized group fed with sucrose with thermal latency being decreased in the fourth week. During weeks 12-18, thermal latency increased compared to that of the hypoestrogenic control. There were no differences in basal blood glucose levels at the 4th and 17th weeks; however, oral glucose tolerance, insulin, and uric acid levels were altered. This indicated that increased body weight and fat as well as alteration sin glucose tolerance, hyperinsulinemia and hyperuricemia, may be associated with the biphasic nociceptive response. Drug Dev Res 77 : 258-266, 2016. © 2016 Wiley Periodicals, Inc.

Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats

Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016.   © 2016 Wiley Periodicals, Inc.

Antinociceptive effects of a new sigma-1 receptor antagonist (N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamide) in two types of nociception

Pain has become an active clinical challenge due its etiological heterogeneity, symptoms and mechanisms of action. In the search for new pharmacological therapeutic alternatives, sigma receptors have been proposed as drug targets. This family consists of sigma-1 and sigma-2 receptors. The sigma-1 system is involved in nociception through its chaperone activity. Additionally, it has been shown that agonist to these receptors promote related sensitisation and pain hypersensitisation, suggesting the possible use of antagonists for sigma-1 receptors as an alternative therapy. The aim of this study was to evaluate the antinociceptive effect of a new sigma-1 receptor antagonist N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamida (NMIN) in two types of pain (arthritic and neuropathic) and to compare its efficacy and potency with reference drugs. The antinociceptive effects of NMIN were quantitatively evaluated using the pain-induced functional impairment model in the rat and the acetone test in a rat model of neuropathic pain. NMIN (sigma-1 receptor affinity of 324nM) did not show any antinociceptive activity in the arthritic pain model but showed a dose-dependent anti-allodynic effect in neuropathic pain. NMIN showed a similar efficacy compared to the effects obtained with morphine and the sigma-1 antagonist BD-1063. However, these reference drugs showed increased potency compared with NMIN. Our results suggest that sigma-1 receptors may play an important direct role in neuropathic pain but not in arthritic pain, supporting the hypothesis that NMIN may be useful for the treatment of neuropathic pain.

Effect of tramadol on metamizol pharmacokinetics and pharmacodynamics after single and repeated administrations in arthritic rats

Combined administration of certain doses of opioid compounds with a non-steroidal anti-inflammatory drug can produce additive or supra-additive effects while reducing unwanted effects. We have recently reported that co-administration of metamizol with tramadol produces antinociceptive effect potentiation, after acute treatment. However, none information about the effect produced by the combination after chronic or repeated dose administration exists. The aims of this study were to investigate whether the antinociceptive synergism produced by the combination of metamizol and tramadol (177.8 + 17.8 mg/kg, s.c. respectively) is maintained after repeated treatment and whether the effects observed are primarily due to pharmacodynamic interactions or may be related to pharmacokinetics changes. Administration of metamizol plus tramadol acute treatment significantly enhanced the antinociceptive effect of the drugs given alone (P < 0.05). Nevertheless, this effect decreased about 53% after the chronic treatment (3 doses per day, for 4 days). No pharmacokinetic interaction between metamizol and tramadol was found under acute treatment (P > 0.05). The mechanism involved in the synergism of the antinociceptive effect observed with the combination of metamizol and tramadol in single dose cannot be attributed to a pharmacokinetic interaction, and other pharmacodynamic interactions have to be considered. On the other hand, when metamizol and tramadol were co-administered under repeated administrations, a pharmacokinetic interaction and tolerance development occurred. Differences found in metamizol active metabolites’ pharmacokinetics (P < 0.05) were related to the development of tolerance produced by the combination after repeated doses. This work shows an additional preclinical support for the combination therapy. The clinical utility of this combination in a suitable dose range should be evaluated in future studies.

Nauclea latifolia Smith (Rubiaceae) exerts antinociceptive effects in neuropathic pain induced by chronic constriction injury of the sciatic nerve

ETHNOPHARMACOLOGICAL RELEVANCE

The roots of Nauclea latifolia Smith (Rubiaceae) popularly known as "koumkouma" is used in traditional Cameroonian medicine as neuropathic pain remedy and for the treatment of headache, inflammatory pain and convulsion. This study was conducted to evaluate the antinociceptive effects of the alkaloid fraction isolated from Nauclea latifolia in neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rat.

MATERIALS AND METHODS

Bioactive-guided fractionation of the root extracts of Nauclea latifolia using the Von Frey in a rat model of neuropathic pain (Benett model), afforded a potent anti-hyperalgesic fraction IV. Further fractionation of this fraction was performed by high-performance liquid chromatography (HPLC), yielded eight sub-fractions (F1-F8) which were tested for antinociceptive effects. The alkaloid fraction (F3) collected by HPLC, exhibited potent antinociceptive effects, and the anti-allodynic and anti-hyperalgesic effects of this fraction (8, 16, 40 and 80 mg/kg) were determined using the von Frey and acetone tests respectively in a rat model of neuropathic pain. Rota-rod performance and catalepsy tests were used for the assessment of motor coordination.

RESULTS

The alkaloid fraction (80 mg/kg) administered intraperitoneally induced a completely decreased hyperalgesia 90 min post-dosing. In the acetone test, the Nauclea latifolia fraction at 80mg/kg showed its maximal anti-allodynic effects 120 min post-injection. The areas under the curve (AUC) of the anti-allodynic or anti-hyperalgesic effects produced by the alkaloid fraction at 80 mg/kg were significantly (p<0.001) greater than the AUC of effects produced by vehicle in CCI rats. The alkaloid fraction did not exhibit any significant effects on the spontaneous locomotor activity of the mice in rota-rod performance and no sign of catalepsy was observed.

CONCLUSION

The analysis of the effects, expressed as the time course of AUC, supports the traditional use of Nauclea latifolia in neuropathic pain therapy. The pharmacological and chemical studies are continuing in order to characterize the mechanism(s) responsible for this anti-hyperalgesic and anti-allodynic action and also to identify the active substances present in the roots extracts of Nauclea latifolia.

Anti-nociceptive and anti-inflammatory activities of the Agastache mexicana extracts by using several experimental models in rodents

ETHNOPHARMACOLOGICAL RELEVANCE

Agastache mexicana is a plant that has long been used in large demand in Mexican folk medicine to treat pain, among others affections. Nevertheless, no scientific data confirming its use have been reported. The aim of this investigation was to examine the spectrum of antinociceptive activity of A. mexicana by using different experimental models of nociception in rodents.

MATERIAL AND METHODS

Nociceptive activity was induced 30 min post treatment of different doses of hexane, ethyl acetate and methanol extracts from A. mexicana aerial parts. The writhing test in mice, and the formalin and plantar tests as well as the pain-induced functional impairment assay in rats (PIFIR model) were the experimental nociceptive models used. Antinociceptive response of the organic extracts was compared to that observed with the analgesic drug tramadol.

RESULTS

A. mexicana organic extracts produced a dose-dependent and significant inhibition of the abdominal constrictions caused by 1% acetic acid injection (i.p.) in mice. A maximal antinociceptive effectiveness obtained with tramadol was also observed with the administration of hexane and ethyl acetate extracts in comparison to less effectiveness obtained with the methanol extract. At the same range of doses, A. mexicana organic extracts inhibited the behavioral responses in both phases of the formalin pain test, in which a more intense effect was observed in the inflammatory phase than in the neurogenic stage. With regard to the plantar test and PIFIR model, a significant but not dose-dependent antinociceptive response was observed at specific doses that depended on the organic extract evaluated.

CONCLUSION

The antinociceptive activity of A. mexicana aerial parts depends on the intensity of the painful stimulus induced and involves different kinds of constituents. Our present results reinforce the use of this species in traditional medicine and its utility for pain treatment mainly associated with inflammation.

Antinociceptive activity of Tilia americana var. mexicana inflorescences and quercetin in the formalin test and in an arthritic pain model in rats

Tilia species are well known around the world for their properties in traditional medicine. Antinociceptive activity of hexane, methanol and aqueous extracts from Tilia americana var. mexicana inflorescences was evaluated in the pain-induced functional impairment model in rats (PIFIR). A preliminar 300 mg/kg dosage of aqueous extracts i.p., but not the same dose of methanol or hexane extract, produced an antinociceptive response in rats similar to that of tramadol (17.8 mg/kg i.p.). A dose-response curve from aqueous extract allowed the determination of ED(50) = 364.97 mg/kg in comparison to ED(50) = 10.35 mg/kg for tramadol in this model. A previous HPLC-DAD analysis corroborated by an HPLC-MS technique in this study demonstrated the flavonoid composition in this Tilia aqueous extract revealing the presence of glycosides mainly derived from quercetin. Thus, Tilia aqueous extract and quercetin were tested at 30 and/or 100 mg/kg dosages i.p. in the PIFIR and formalin models producing a significant and dose-dependent antinociceptive response resembling that produced by a total and a partial agonist of 5-HT(1A) receptors like 8-OH-DPAT (0.1 mg/kg, s.c.) and buspirone (5 mg/kg, i.p.), respectively. In all the treatments, antinociceptive response was inhibited in the presence of WAY 100635 (0.12 mg/kg, i.p.). Our results support the analgesic activity of T. americana var. mexicana inflorescences attributed by folk medicine; they also indicate that quercetin is partly responsible for this pharmacological activity that is likely mediated by serotonin 5-HT(1A) receptors.

Dopamine receptors in the anterior insular cortex modulate long-term nociception in the rat

The rostral agranular insular cortex (RAIC) receives dopaminergic projections from the mesolimbic system, which has been involved in the modulation of nociceptive processes. In this study we determined the contribution of dopamine D(1) and D(2) receptors in the RAIC regarding nociception processing in a neuropathic pain model, as well as inflammatory articular nociception measured as pain-induced functional impairment in the rat (PIFIR). Microinjection of vehicle or substances into the RAIC was performed after the induction of nociception. The groups were treated with: a dopamine D(1) receptor antagonist (SCH-23390), a dopamine D(1) receptor agonist (SKF-38393), a dopamine D(2) receptor agonist (TNPA) and a dopamine D(2) receptor antagonist (spiperone). Chronic nociception, induced by denervation, was measured by the autotomy score in which onset and incidence were also determined. The SCH-23390 and TNPA groups showed a decrease in the autotomy score and a delay on the onset as compared to control, whereas the PIFIR groups did not show statistical differences. This work shows the differential role of dopamine receptors within the RAIC in which the activation of D(2) or the blockade of D(1) receptors elicit antinociception.

Co-administration of rofecoxib and tramadol results in additive or sub-additive interaction during arthritic nociception in rat

Over the decades, nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids are the most commonly used analgesics in the management of acute and chronic pain. In order to assess a possible antinociceptive interactions, the antinociceptive effects of rofecoxib p.o., a preferential inhibitor of cyclooxygenase-2, and tramadol-hydrochloride p.o., an atypical opioid analgesic, administered either separately or in combination, were determined using a rat model of arthritic pain. The data were interpreted using the surface of synergistic interaction (SSI) analysis and an isobolographic analysis to establish the nature of the interaction. The SSI was calculated from the total antinociceptive effect produced by the combination after subtraction of the antinociceptive effect produced by each individual drug. Female rats received orally rofecoxib alone (1.0, 1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg), tramadol alone (1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg) or 12 different combinations of rofecoxib plus tramadol. Five combinations exhibited various degrees of sub-additive (i.e. less than the sum of the effects produced by the each drug alone) antinociceptive effects (3.2 mg/kg tramadol with 7.8 mg/kg rofecoxib; 5.6 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib; 10.0 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib), whereas the other 7 combinations showed additive antinociceptive effects (i.e. the sum of the effects produced by each agent alone). Three combination of rofecoxib+tramadol (10.0+5.6, 10.0+10.0, and 17.8+5.6 mg/kg respectively) presented high sub-additive interactions (P<0.002: Q=9.5). The combination rofecoxib (17.8 mg/kg)+tramadol (10.0 mg/kg) caused gastric injuries less severe than those observed with indomethacin, but more severe than those obtained with rofecoxib or tramadol in single administration. The antinociceptive interaction of rofecoxib and tramadol suggests that combinations with these drugs may have no clinical utility in pain therapy.

Evaluation of the antinociceptive effect of Rosmarinus officinalis L. using three different experimental models in rodents

The rationale of this investigation was to examine the antinociceptive effect of an ethanol extract of Rosmarinus officinalis (RO) aerial parts, using three different experimental models: acetic acid-induced writhing test and formalin test in mice; and a model of arthritic pain: "pain-induced functional impairment model in the rat (PIFIR model)". The antinociceptive efficacies were evaluated using several dose-response curves and time courses. The antinociceptive effects from RO extract were compared with the antinociceptive effect of either tramadol (TR: 3.16-50 mg/kg, i.p. in mice, and 1.0-31.62 mg/kg, i.p. in rats) or acetylsalicylic acid (AA: 31.62-562.32 mg/kg, p.o.). RO extract (10-300 mg/kg, p.o.) significantly (P < 0.001) reduced the number of writhing movement induced by the i.p. administration of acetic acid solution in a dose-dependent way (ED50 = 108.84 mg/kg, whereas, TR showed an ED50 = 12.38 mg/kg). In addition, RO extract (30-300 mg/kg) significantly (P < 0.001) inhibited licking and shaking behaviours in both early (neurogenic pain) and in the late (inflammatory pain) phases of the formalin test. These effects were like those produced by TR. Concerning the results using the PIFIR model, RO extract (30-3000 mg/kg, p.o.) like either TR or AA, produced a significant (P < 0.001) and dose-dependent antinociceptive response in rats (RO: ED50 = 222.78 mg/kg versus TR: ED50 = 11.06 mg/kg and AA: ED50 = 206.13 mg/kg). These results strongly suggest that aerial parts of RO possess antinociceptive and anti-inflammatory activity, and reinforce the use of this plant in folk medicine.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.

Enhancement of antinociception by co-administration of ibuprofen and caffeine in arthritic rats

It has been observed that caffeine improves antinociceptive efficacy of some non-steroidal antiinflammatory drugs (NSAIDs) in several experimental models, however, these effects have been questioned in humans. Controversy in clinical studies may be due to the use of different protocols as well as to high interindividual variability in patient response. In addition, the antinociceptive interaction of ibuprofen+caffeine has not been studied. To assess a possible synergistic antinociceptive interaction, the antinociceptive effects of ibuprofen, and caffeine administered either separately or in combinations were determined in a model of arthritic pain: "Pain-induced functional impairment in the rat (PIFIR model). The antinociceptive efficacies were evaluated using several dose-response curves and time courses. The antinociceptive effects from the combination that produced the greater effect were compared with the maximal antinociceptive effect of either morphine or acetylsalicylic acid alone. The animals were administered with 0.05 ml intra-articular (i.a.) of uric acid to induce nociception. Groups of six rats received either acetylsalicylic acid, morphine, ibuprofen or caffeine, or a combination ibuprofen+caffeine (18 combinations). We report here that caffeine (17.8 and 31.6 mg/kg) is able to potentiate the antinociceptive effect of ibuprofen. This investigation showed that six combinations presented effects of potentiation and twelve combinations only showed antinociceptive effects not different from that of ibuprofen alone. The maximum antinociceptive effect was 270.7+/-12.7 area units (au), produced by ibuprofen 100 mg/kg+caffeine 17.8 mg/kg; this effect was greater than the maximum produced by morphine 17.8 mg/kg (244.7+/-22.9 au) in these experimental conditions. The maximum potentiation was 197 % produced with the combination of ibuprofen 17.8 mg/kg+caffeine 17.8 mg/kg. These results suggest that the antinociceptive effect of ibuprofen was significantly potentiated by doses of caffeine that by themselves are ineffective in this model.

Influence of inflammatory nociception on the anxiolytic-like effect of diazepam and buspirone in rats

RATIONALE

The effect of anxiety on nociception has been evaluated but not that of nociception on anxiety.

OBJECTIVE

The study was conducted to analyse the influence of nociception on basal levels of anxiety-like behaviour and on the action of anxiolytic drugs.

METHODS

Nociception was induced by an intra-articular injection of uric acid at 3.75 or 7.5%. Experimental anxiety was determined in the rat burying behaviour and the elevated plus maze tests. To separate specific anxiety-related drug actions, a spontaneous ambulatory test was included. The anxiolytics, buspirone (2.5 and 5.0 mg/kg, i.p.) and diazepam (0.5, 1.0 and 2.0 mg/kg, i.p.), were used.

RESULTS

In the nociception test, the pain-induced functional impairment rat model, uric acid at 3.75 and 7.5% had an effect of around 35 and 75%, respectively. Uric acid (UA) at the lower dose (3.75%) lacked an effect on burying behaviour but significantly increased the time spent and number of entries to the open arms; the higher UA dose (7.5%) produced a significant increase in the time spent and number of entries to the open arms and a statistically significant reduction in cumulative burying. Diazepam and buspirone produced a clear dose-dependent reduction in cumulative burying. In the plus maze, diazepam also induced an increase in the time spent and number of entries to the open arms. In the burying behaviour test, rats with a mild level of nociception (uric acid at 7.5%) were insensitive to the anxiolytic-like effect of these anxiolytic drugs. In the plus maze test, the anxiolytic-like effect of diazepam (1.0 mg/kg) was blocked under both levels of nociception.

CONCLUSIONS

These data demonstrate that nociception modifies the response to anxiolytic drugs. The role of factors with anxiogenic properties produced during inflammation, which may modify diazepam and buspirone effects, is discussed.

Peripheral involvement of the nitric oxide-cGMP pathway in the indomethacin-induced antinociception in rat

The role of nitric oxide (NO) in the antinociceptive effect of indomethacin was assessed in the pain-induced functional impairment model in the rat (PIFIR model), a model of inflammatory and chronic pain similar to that observed in clinical gout. Oral administration of indomethacin (5.6 mg/kg), a nonselective cyclooxygenase inhibitor, significantly decreased the nociceptive response elicited by uric acid injected into the knee joint of the right hind limb (2.0+/-3.0 and 149.7+/-18.0 area units [au], in the absence and the presence of indomethacin, respectively). This effect of indomethacin was reduced in nearly 50% by local pretreatment with the nonselective inhibitor of NO synthase, N G-L-nitro-arginine methyl ester (L-NAME) (72.9+/-10.7 vs. 149.7+/-18.0 au, P<0.05). On the other hand, local administration of L-arginine (a NO synthase substrate) or sodium nitroprusside (a non-enzymatic NO donor) each increased in almost 40% the antinociceptive effect of indomethacin (230.9+/-12.6 and 226.6+/-9.7 vs. 149.7+/-18.0 au, P<0.05), whereas D-arginine (the inactive isomer of arginine) had no effect on the indomethacin antinociceptive response (208.0+/-34.9 vs. 149.7+/-18.0 au). These results suggest that, the antinociceptive effect of indomethacin involves, at least in part, the NO-cyclic GMP pathway at peripheral level.

Antinociceptive activities of aqueous and ethanolic extracts of Alpinia calcarata rhizomes in rats

Rhizomes of Alpinia calcarata Roscoe (Zingiberaceae) posses several bio-activities and are used in traditional medicine of Sri Lanka. However, their antinociceptive activity has not been investigated so far. The aim of this study therefore, was to examine the antinociceptive activity of hot water extract (HWE) and hot ethanol extract (HEE) of Alpinia calcarata rhizomes using rats and three models of nociception (tail flick, hot plate and formalin tests). Different concentrations of HWE (100, 250, 500, 750, 1000 mg/kg) and HEE (100, 250, 500, 750, 1000 mg/kg) were made and orally administrated to rats and the reaction times determined. The results showed that the extracts have marked dose-dependent antinociceptive activity, when evaluated in the hot plate and the formalin tests but not in the tail flick test. The antinociceptive effect was slightly higher in HEE than that of HWE. The antinociceptive effect was mediated via opioid mechanisms.

Evidence for a central mechanism of action of S-(+)-ketoprofen

It has been observed that some non-steroidal anti-inflammatory drugs (NSAIDs) may act through several mechanisms, in addition to central inhibition of prostaglandin synthesis. These other mechanisms include the L-arginine-nitric oxide (L-arginine-NO) pathway, as well as endogenous opiate and serotonergic mechanisms. Some of these mechanisms can explain the efficacy of NSAIDs in chronic pain conditions such as rheumatoid arthritis. The present study was designed to elucidate the involvement of the above pathways/mechanisms in the antinociceptive effect of S-(+)-ketoprofen at supraspinal and spinal levels. S-(+)-ketoprofen induced dose-dependent antinociception in the pain-induced functional impairment model in the rat. The antinociceptive effect of S-(+)-ketoprofen was not altered by i.t. or intracerebroventricula (i.c.v.) pre-treatment with L-arginine (29.6 microg/site) and L-nitro-arginine-monomethylester (L-NAME) (21.1 microg/site) and neither was the effect of S-(+)-ketoprofen modified by the opiate antagonist, naloxone (1 mg/kg, s.c.). In marked contrast, both i.c.v. administration of the 5-hydroxytryptamine (5-HT)(1)/5-HT(2)/5-HT(7) receptor antagonist, methiothepin (1.5 microg/site), and i.t. administration of the 5-HT(3)/5-HT(4) receptor antagonist, tropisetron (0.9 microg/site), significantly inhibited the S-(+)-ketoprofen-induced antinociceptive effect. These data suggest that the antinociceptive response to S-(+)-ketoprofen involves serotoninergic mechanisms via both supraspinal 5-HT(1)/5-HT(2)/5-HT(7) receptors and 5-HT(3) receptors located at spinal level. A role of the L-arginine-NO and opiate systems in S-(+)-ketoprofen-induced antinociception in the pain-induced functional impairment model in the rat model seems unlikely.

Participation of the L-arginine-nitric oxide-cyclic GMP-ATP-sensitive K+ channel cascade in the antinociceptive effect of rofecoxib

The antinociceptive effect of rofecoxib, a preferential inhibitor of cyclooxygenase-2, was assessed in the pain-induced functional impairment model in the rat. Systemic administration of rofecoxib generated a dose-dependent antinociceptive effect in rats injected with uric acid into the knee joint of the right hindlimb in order to produce nociception. Ipsilateral intra-articular pretreatment with N(G)-L-nitro-arginine methyl ester (L-NAME, an inhibitor of nitric oxide (NO) synthesis), 1H-(1,2,4)-oxadiazolo (4,2-a)quinoxalin-1-one (ODQ, an inhibitor soluble guanylyl cyclase), and the ATP-sensitive potassium channel blocker glibenclamide reversed the antinociceptive effect of rofecoxib p.o. However, ipsilateral intra-articular pretreatment with L-arginine (a NO substrate), or 3-morpholino-sydnonimine-HCl (SIN-1, a non-enzymatic donor of NO), potentiated the antinociceptive effect induced by rofecoxib. The present results suggest that, in addition to cyclooxygenase-2 inhibition, the antinociceptive effect of rofecoxib could also involve activation of the L-arginine-NO-cyclic GMP (cGMP) pathway, followed by opening of ATP-sensitive K+ channels at the peripheral level.

Analysis of the analgesic interactions between ketorolac and tramadol during arthritic nociception in rat

The potential advantage of using combination therapy is that analgesia can be maximized while minimizing the incidence of adverse effects. In order to assess a possible synergistic antinociceptive interactions, the antinociceptive effects of ketorolac tromethamine, p.o., a nonsteroidal anti-inflammatory drug (NSAID), and tramadol hydrochloride, p.o., an atypical opioid analgesic, administered either separately or in combination, were determined using a rat model of arthritic pain. The data were interpreted using the surface of synergistic interaction (SSI) analysis and an isobolographic analysis to establish the nature of the interaction. The surface of synergistic interaction was calculated from the total antinociceptive effect produced by the combination after subtraction of the antinociceptive effect produced by each individual drug. Female rats received orally ketorolac alone (0.18, 0.32, 0.56, 1.0, 1.78, 3.16, and 5.62 mg/kg), tramadol alone (3.16, 5.62, 10.0, 17.78, 31.62, 56.23, and 100.0 mg/kg), or 24 different combinations of ketorolac plus tramadol. Ten combinations exhibited various degrees of potentiation of antinociceptive effects (17.78 mg/kg tramadol with either 0.18, 0.32, or 0.56 mg/kg ketorolac; 10.0 mg/kg tramadol with either 0.18, 0.32, 0.56, or 1.8 mg/kg ketorolac; 5.6 mg/kg tramadol with either 0.32 or 0.56 mg/kg ketorolac; and 3.16 mg/kg tramadol with 0.32 mg/kg ketorolac), whereas the other 14 combinations showed additive antinociceptive effects. Three combinations of ketorolac+tramadol (1.0+17.78, 1.78+10, and 1.78+17.78, mg/kg respectively) produced the maximum antinociceptive effects, and two combinations (0.32+10.0 and 0.56+10.0 mg/kg, respectively) presented effects of high potentiation (P<0.001). This combination caused gastric injuries less severe than those observed with indomethacin. The synergistic antinociceptive effects of ketorolac and tramadol were important and suggest that combinations with these drugs may have clinical utility in pain therapy.

Enhancement of antinociception by co-administration of an opioid drug (morphine) and a preferential cyclooxygenase-2 inhibitor (rofecoxib) in rats

Synergism has been used to obtain analgesia at doses at which side effects are minimal. In addition, it has been demonstrated that inhibition of cyclooxygenase-2 is responsible for the therapeutic effects of nonsteroidal anti-inflammatory drugs (NSAIDs). The aim of this study was to evaluate the antinociceptive interaction between the preferential COX-2 inhibitor, rofecoxib and morphine. Several combinations were evaluated using the pain-induced functional impairment model (PIFIR), a rat model of arthritic pain. Surface of synergistic interaction (SSI) analysis and an isobolographic method were used to detect the antinociceptive potency of the drugs, given either individually or in combination. The surface of synergistic interaction was calculated from the total antinociceptive effect produced by the combination after subtraction of the antinociceptive effect produced by each individual drug. Male rats received orally morphine alone (10, 17.8, 31.6, 56.2 and 100.0 mg/kg), rofecoxib alone (3.2, 5.6, 10, 31.6, 56.2 and 74.0 mg/kg) or 12 different combinations of morphine and rofecoxib. Three combinations exhibited potentiation of antinociceptive effects (10 mg/kg of morphine with either 5.6, 10 or 31.6 mg/kg of rofecoxib), whereas the other nine combinations showed additive antinociceptive effects. The combination of morphine, 56.2 mg/kg (p.o.), and rofecoxib, 31.6 mg/kg (p.o.), produced the maximum antinociceptive effect (P<0.05). This combination caused gastric injuries less severe than those observed with indomethacin, i.e. it reduced ulcers and erosion formation. The synergistic antinociceptive effects of rofecoxib and morphine are important and suggest that combinations with drugs may decrease the side effects associated with the use of nonselective NSAIDs. Furthermore, the present results suggest that combinations containing opioid drugs and selective COX-2 inhibitors may have clinical utility in pain therapy.

Metamizol potentiates morphine antinociception but not constipation after chronic treatment

This work evaluates the antinociceptive and constipating effects of the combination of 3.2 mg/kg s.c. morphine with 177.8 mg/kg s.c. metamizol in acutely and chronically treated (once a day for 12 days) rats. On the 13th day, antinociceptive effects were assessed using a model of inflammatory nociception, pain-induced functional impairment model, and the charcoal meal test was used to evaluate the intestinal transit. Simultaneous administration of morphine with metamizol resulted in a markedly antinociceptive potentiation and an increasing of the duration of action after a single (298+/-7 vs. 139+/-36 units area (ua); P<0.001) and repeated administration (280+/-17 vs. 131+/-22 ua; P<0.001). Antinociceptive effect of morphine was reduced in chronically treated rats (39+/-10 vs. 18+/-5 au) while the combination-induced antinociception was remained similar as an acute treatment (298+/-7 vs. 280+/-17 au). Acute antinociceptive effects of the combination were partially prevented by 3.2 mg/kg naloxone s.c. (P<0.05), suggesting the partial involvement of the opioidergic system in the synergism observed. In independent groups, morphine inhibited the intestinal transit in 48+/-4% and 38+/-4% after acute and chronic treatment, respectively, suggesting that tolerance did not develop to the constipating effects. The combination inhibited intestinal transit similar to that produced by morphine regardless of the time of treatment, suggesting that metamizol did not potentiate morphine-induced constipation. These findings show a significant interaction between morphine and metamizol in chronically treated rats, suggesting that this combination could be useful for the treatment of chronic pain.

Involvement of peripheral cyclooxygenase-1 and cyclooxygenase-2 in inflammatory pain

Pain-induced functional impairment in the rat (PIFIR) is a model of inflammatory and arthritic pain similar to that of clinical gout. Nociception is induced by the intra-articular injection of uric acid into the right hind limb, inducing its dysfunction. Animals then receive analgesic drugs and the recovery of functionality over time is assessed as an expression of antinociception. We have examined the role of peripheral prostaglandins synthesized by cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) in inflammatory pain using the PIFIR model. Rofecoxib (a selective COX-2 inhibitor) and SC-560 (a selective COX-1 inhibitor) both produced dose-dependent effects. When the inhibitors were administered before uric acid, they showed similar potency, but the antinociceptive efficacy of SC-560 was lower than rofecoxib; the best antinociceptive effects were obtained with the dose of 100 microg/articulation of each inhibitor (pre-treatment). In post-treatment (inhibitors administered after the uric acid), rofecoxib showed the least antinociceptive effect and SC-560 was more potent than rofecoxib. The inhibition of both COX-1 and COX-2 produced a more profound analgesic effect than the inhibition of either COX-1 or COX-2 alone. The present data support the idea that both COX isoforms contribute to the development and maintenance of local inflammatory nociception. Thus, it could be expected that inhibition of both COX-1 and COX-2 is required for non-steroidal anti-inflammatory drugs (NSAID)-induced antinociception in the rat. These findings suggest that the therapeutic effects of NSAIDs may involve, at least in part, inhibition of COX-1 and COX-2.

Effect of caffeine on antinociceptive action of ketoprofen in rats

BACKGROUND

To assess a possible synergistic antinociceptive interaction, the antinociceptive effects of ketoprofen (KET), and caffeine (CAF) administered either separately or in combinations were determined in a model of arthritic pain.

METHODS

Antinociceptive activity was assayed using "ellipsis pain-induced functional impairment in the rat" (PIFIR model). The antinociceptive efficacies were evaluated using several dose-response curves and time courses. The antinociceptive effects from the combination that produced the greater effect were compared with the maximal antinociceptive effect of either morphine, acetylsalicylic acid (ASA), or KET alone. The animals were administered with 0.05 mL intra-articular (i.a.) of uric acid to induce nociception. Groups of six rats received orally either ASA, morphine (MOR), KET, CAF, or a combination KET + CAF (24 combinations).

RESULTS

ASA (ED(50) 465.2 +/- 1.5 mg/kg), MOR (ED(50) 71.0 +/- 1.6 mg/kg), and KET (ED(50) 7.2 +/- 1.4 mg/kg) alone induced dose-dependent antinociception, whereas CAF alone showed no activity at the assayed doses. Nine combinations showed various degrees of potentiation (p <0.01), while the remainder exhibited the antinociceptive effect of KET only. Combinations of 17.8 mg/kg CAF with either 1.0, 1.8, 3.2, 5.6, or 10.0 mg/kg KET yielded the highest antinociceptive potentiations. For example, antinociceptive effect was 125.6 +/- 21.4 area units (au) with KET (3.2 mg/kg) alone, but the combination with CAF (17.8 mg/kg) showed 309.5 +/- 10.3 au. The median effective dose (ED(50)) of KET alone was 7.2 +/- 1.4 mg/kg, whereas the ED(50) of KET + CAF 17.8 mg/kg was 0.4 +/- 0.6 mg/kg: KET in the presence of CAF was approximately 18 times more potent than the analgesic drug without CAF.

CONCLUSIONS

These results showed that CAF was able to potentiate the analgesia of KET, but only at selected dose combinations: CAF in the doses of 10.0 and 17.8 mg/kg was able to potentiate the analgesic effect of KET, the most efficacious drug combination being CAF 17.8 mg/kg + KET 3.2 mg/kg. The combination of analgesic drugs and CAF can produce better antinociceptive effects than the analgesic drug alone. This knowledge will permit the selection of the therapeutically most effective combination ratio of drugs, employing lower doses of each drug.

Characterization of the potentiation of the antinociceptive effect of diclofenac by vitamin B complex in the rat

The role of vitamin B complex preparations as an analgesic adjuvant is controversial. Therefore, the purpose of the present study was to characterize the potentiation of the antinociceptive effect of diclofenac by a vitamin B complex preparation and its individual components by using the pain-induced functional-impairment model in the rat (PIFIR). Pain was produced by the intraarticular injection of uric acid in the right hind limb. Oral administration of diclofenac resulted in a dose-dependent antinociceptive effect. Oral administration of a vitamin B complex preparation containing thiamine (vitamin B(1)), pyridoxine (vitamin B(6)), and cyanocobalamin (vitamin B(12)) in a 1:1:0.01 proportion did not produce any antinociception by itself, but it significantly potentiated the effect of diclofenac. Coadministration of diclofenac with either thiamine or pyridoxine resulted in an antinociceptive effect similar to that of diclofenac alone. On the other hand, coadministration of cyanocobalamin significantly increased diclofenac-induced antinociception. It is concluded that the potentiation of diclofenac-induced antinociception in the PIFIR model is due to cyanocobalamin.

A review of the pharmacokinetic and pharmacodynamic factors in the potentiation of the antinociceptive effect of nonsteroidal anti-inflammatory drugs by caffeine

Caffeine is an effective analgesic adjuvant because it increases the antinociceptive effect of NSAIDs while reducing the probability of side effects. The mechanism by which caffeine increases the antinociceptive action of NSAIDs does not appear to include a pharmacokinetic interaction. The potentiation appears to be due to a pharmacokinetic mechanism including actions at the central and the peripheral levels. Because caffeine shifts the effect-compartment concentration-effect relation of NSAIDs to the left and this relationship is sigmoidal, there is no potentiation if the NSAID concentrations are too high or too low with respect to EC(50). The best potentiation can be observed if the NSAID doses used yield effect-compartment concentrations in the vicinity of EC(50). Therefore further investigation of the PK/PD relations of caffeine-NSAID combinations for different pain states and intensities is needed to optimize the therapeutic use of these mixtures.

Effect of coadministration of caffeine and either adenosine agonists or cyclic nucleotides on ketorolac analgesia

Caffeine potentiation of ketorolac-induced antinociception in the pain-induced functional impairment model in rats was assessed. Caffeine alone was ineffective, but increased the effect of ketorolac without affecting its pharmacokinetics. Intra-articular administration of adenosine and N6-cyclohexyladenosine (CHA, an adenosine A1 receptor agonist), but not 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680, an adenosine A2A receptor agonist), significantly increased ketorolac antinociception. This effect was not local, as contralateral administration was also effective. Ipsilateral and contralateral administration of adenosine and CHA also increased antinociception by ketorolac-caffeine. Intra-articular 8-Bromo-adenosine cyclic 3',5'-hydrogen phosphate sodium or 8-Bromo-guanosine-3',5'-cyclophosphate sodium (cGMP) given ipsilaterally or contralaterally did not affect ketorolac-induced antinociception. Nevertheless, ipsilateral, but not contralateral, administration of 8-Br-cGMP significantly increased antinociception by ketorolac-caffeine, suggesting a local effect. The results suggest that caffeine potentiation of ketorolac antinociception is mediated, at least partially, by a local increase in cGMP and rule out the participation of adenosine receptor blockade.

Effect of caffeine coadministration and of nitric oxide synthesis inhibition on the antinociceptive action of ketorolac

The effects of caffeine and nitric oxide synthesis inhibition on the antinociceptive action of ketorolac were assessed using the pain-induced functional impairment model in the rat. Nociception was induced by the intra-articular injection of uric acid. Ketorolac, but not caffeine, produced an antinociceptive effect which was reduced by NG nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis. Caffeine coadministration potentiated the ketorolac effect. L-NAME induced a dose-dependent reduction of this potentiation. The results suggest the participation of the L-arginine-nitric oxide-cyclic GMP pathway in the caffeine potentiation of ketorolac-induced antinociception.