Analgesic effects of N-acetyl-5HTP-5HTP amide are not directly related to brain serotonin levels.

A synthetic dipeptide, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, was shown previously to inhibit the binding of serotonin to a soluble specific serotonin binding protein as well as to alter brain serotonin levels. When injected into rats intraventricularly, the dipeptide caused an increase in pain threshold, lasting for several hours, as determined by either a flinch-jump test or a tail-flick test. This effect was reversed by naloxone. The dipeptide is a very weak inhibitor of the binding of labelled naloxone or dihydromorphine to a membranous opiate receptor preparation. The analgesic activity of the dipeptide was not diminished by p-chlorophenylalanine or the setonergic neurotoxin 5,7-dihydroxytryptamine, which depleted brain serotonin levels. This implies that the analgesic action of the dipeptide is not mediated directly by its effect on serotonin concentration.     

Comparative analysis of analgesic activities of dermorphin, [DPro<Superscript>6</Superscript>]-dermorphin,and their C-terminal tripeptides

Analgesic activities of dermorphin (DM), [DPro⁶]-DM, and their C-terminal tripeptides were comparatively studied. Analgesic activity was evaluated in tail flick, hot plate, tail pinch, formalin, and acetic acid writhing tests describing different levels of organization of pain sensitivity. Intraperitoneal administration of the peptides decreased the pain threshold in all these tests. The C-terminal tripeptides DM_5–7 and [DPro⁶]-DM_5–7 demonstrated analgesics activity comparable or sometimes higher than that of the full-length molecules. The effect of DM, [DPro⁶]-DM, and C-terminals fragments DM_5–7 and [DPro⁶]-DM_5–7 decreased after co-administration with naloxone, which points to the opioid nature of analgesic activity of the peptides.     

Effect of Structural Changes of Pro6 in Dermorphin Molecule on Its Antinociceptive Activity

We studied effect of dermorphin (H-Tyr-DAla-Phe-Gly-Tyr-Pro-Ser-NH₂) and its analogs with modified amino acid residue proline in position 6, H-Tyr-DAla-Phe-Gly-Tyr-[DPro]-Ser-NH₂, H-Tyr-DAla-Phe-Gly-Tyr-[dehydro-Pro]-Ser-NH₂, and H-Tyr-DAla-Phe-Gly-Tyr-[D-dehydro-Pro]-Ser-NH₂, on nociception in the tail-flick and hot plate tests after intraperitoneal injection. Replacement of LPro with the stereoisomer DPro as well as Pro dehydration (LdHPro) was shown to increase antinociceptive activity. Replacement of LdHPro with DdHPro cancelled the activity in the tail-flick test. All three dermorphin analogs retained antinociceptive activity in the hot plate test; however, the effect of dermorphin was more pronounced.     

Augmentation of analgesic effect of ibuprofen by alprazolam in experimental model of pain

The reports of analgesic effects of benzodiazepines are inconsistent. There is evidence of a hyperalgesic effect induced by activation of supraspinal GABAA receptors and an antinociceptive effect induced by activation of receptors located in the spinal cord (dorsal horns). The aim of the study was to discover whether the systemic administration of a benzodiazepine agent alprazolam increases the systemic analgesic efficacy of non-opioid analgesic ibuprofen. Experimental studies combining these agents have not yet been published. We used three experimental methods - writhing test (with acetic acid), tail-flick test and plantar test to assess analgesic action. The drugs were administered orally. Augmentation of the analgesic effect of ibuprofen by alprazolam was proved for the writhing test at a dose of 30 mg/kg of ibuprofen and alprazolam 1 mg/kg. The reaction time of the combination was significantly prolonged in comparison with ibuprofen alone. The results of the tail-flick test and plantar test were negative. The effect of ibuprofen was not enhanced by alprazolam in tests of acute thermal pain. Our results have demonstrated that the analgesic action of ibuprofen is only weakly enhanced by alprazolam.     

Identification of functionally important dipeptide in sequences of atypical opioid peptides

The occurrence of individual amino acids and dipeptide fragments in the sequences of 60 known atypical opioid peptides was analyzed. An expressed predominance of Tyr-Pro fragment suggested a high probability of analgesic activity for this dipeptide, and it was experimentally studied. It was shown on the somatic and visceral pain sensitivity models that, at the i.p. administration of Tyr-Pro in doses of 1.0–10 mg/kg of body mass, it exhibits an analgesic activity eliminated by naloxone and naloxone metiodide. However, in tests on ileum preparations of guinea pig and mouse vas deference in vitro, Tyr-Pro was devoid of opioid activity, which proved its indirect influence on opioid receptors.     

Study of the relationship between analgesic activity and structure of synthetic melanocortin analogs

Melanocortins, peptides of the family of adrenocorticotropic (ACTH) and melanocyte-stimulating (MSH) hormones, have a wide range of physiological activity. Heptapeptide semax (MEHFPGP) is an analog of the ACTH_4–10 fragment. Previously, pronounced nootropic and neuroprotective activities were shown for this peptide; in addition, it decreases pain sensitivity in animals. In this work, the relationship between analgesic activity of the peptide and its structure was studied. The following analogs of the N-terminal ACTH fragments were used: rMEHFPGP, where r is glucuronic acid, KEHFPGP, GEHFPGP, EHFPGP, HFPGP, and ERP. The peptides were administered intraperitoneally at doses of 0.015, 0.05 and 0.5 mg/kg. Rat pain sensitivity was assessed using the paw-withdrawal test. Truncations of the N-terminal residues eliminated the analgesic activity. The peptide analgesic effect was observed after the replacement of the N-terminal methionine with lysine or after the attachment of glucuronic acid to the methionine, while the peptide with glycine instead of the methionine had no effect on pain sensitivity. Hence, the amino acid at position 1 of semax analogs plays a key role in mediating the analgesic effects of the peptides.     

A spinal site mediates opiate analgesia in frogs

The application of acetic acid to the hind leg of a frog will induce a spinally mediated wiping reflex only if the acetic acid concentration is above a certain threshold. By using this reflex as the basis of a test for nociception, we show that morphine sulfate is a potent analgesic in the frog when injected into the lumbar area of the spinal cord. Significant analgesia is induced within 5 min after injection of as little as 0.0316 μg of morphine sulfate. Low doses of morphine sulfate (0.0316 or 0.1 μg) induce analgesia which dissipates within 1 h while for higher doses (0.316, 1.0 or 3.16 μg) the analgesia persists for at least 3 h. The analgesic effect of 0.316 μg of morphine sulfate is completely blocked by naloxone HCl at either 0.158 or 0.316 μg. Animals receiving naloxone alone (0.316 μg) appear to be slightly hyperalgesic compared to saline injected controls but this effect is not significant.     

Comparison of the behavioral effects of β-endorphin and enkephalin analogs

The behavioral effects of β-endorphin, enkephalin analogs, morphine and etorphine were briefly compared. In the tail-flick test in mice and in the wet shake test in rats, β-endorphin and D-Ala²-D-Leu⁵-enkephalin had equal antinociceptive activity; D-Ala² -Met-enkephalinamide and D-Leu⁵-enkephalin were less active. The order of activity of the enkephalin analogs and opiate alkaloids for stimulating locomotor activity in mice paralleled their analgesic activities; β-endorphin, however, had only minimal stimulatory actions. Morphine sulfate, 50 μg injected into the periaqueductal gray, produced hyperactivity but this effect was not observed with etorphine or opioid peptides. By contrast, “wet dog” shakes was observed with the opioid peptides but not with either opiate alkaloid. These heterogenous behavioral responses, which were all antagonized by naloxone, indicate that multiple types of receptors mediate the effects of opiates in the central nervous system.     

Involvement of NMDA receptors in the analgesic properties of psychotridine.

We have previously reported that the alkaloid extract of Psychotria colorata (Willd. ex R. & S.) Muell. Arg., had marked dose-dependent, opioid-like activity. Phytochemical analyses of P. colorata flowers and leaves identified several pyrrolidinoindoline alkaloids, including psychotridine. To further investigate the activity and mechanism of action of Psychotria alkaloids, we studied the effects of psychotridine on thermal and chemical models of analgesia. In the tail-flick model, psychotridine presents a dose-dependent analgesic effect; the effect is not reversed by prior treatment with naloxone. Psychotridine dose-dependently decreased capsaicin-induced pain. Performance in the rotarod test showed that psychotridine does not induce motor deficits at doses effective in analgesia models. Psychotridine inhibited [3H]MK-801 (dizocilpine) binding to cortex membranes in a dose-dependent manner. Binding is completely abolished at 300 nM. The data rule out opioid activity, and the inhibition of capsaicin-induced pain and of radioligand binding strongly suggest the participation of NMDA receptors in psychotridine-induced analgesia.     

Studies on the analgesic activities of Jia-Yuan-Qing pill and its safety evaluation in mice

The analgesic activity of Porcellio laevis Latreille, Rhizoma Corydalis, and Radix Cynanchi Paniculati have been reported in recent years. A new formula named Jia-Yuan-Qing pill (JYQP) is therefore created by combining the three herbs at 9:7:7 ratio according to traditional Chinese theories. The present study aims to evaluate the effect of JYQP as a novel painkiller in various models. Acute toxicity test was applied to evaluate the safety of JYQP. Acetic-acid-induced writhing, hot plate test, formalin test, and naloxone-pretreated writhing test were employed to elaborate the analgesic activity of JYQP and its possible mechanism. A bone cancer pain mouse model was performed to further assess the effect of JYQP in relieving cancer pain. Test on naloxone-precipitated withdrawal symptoms was conduct to examine the physical dependence of mice on JYQP. Data revealed that JYQP reduced writhing and stretching induced by acetic acid; however, this effect could not be blocked by naloxone. JYQP specifically suppressed the phase II reaction time in formalin-treated mice; meanwhile, no analgesic effect of JYQP in hot plate test was observed, indicating that JYQP exerts analgesic activity against inflammatory pain rather than neurogenic pain. Furthermore, JYQP could successfully relieve bone cancer pain in mice. No physical dependence could be observed upon long-term administration in mice. Collectively, our present results provide experimental evidence in supporting clinical use of JYQP as an effective and safe agent for pain treatment.     

Pharmacological analysis of inhomogeneous static magnetic field-induced antinociceptive action in the mouse

The effect of inhomogeneous, 2-754 mT static magnetic field (SMF) on visceral pain elicited by intraperitoneal injection of 0.6% acetic acid (writhing test) was studied in the mouse. Exposure of mice to static magnetic field (permanent NdFeB N50 grade 10 mm x 10 mm cylindrical magnets with alternating poles) during the nociceptive stimulus (0-30 min) resulted in inhibition of pain reaction: the number of writhings decreased from 9 +/- 2, 32 +/- 4 and 30 +/- 3 to 2 +/- 0.03, 15 +/- 1.6, and 14 +/- 1.6, respectively, measured in 0-5th, 6-20th, and 21-30th min following the acetic acid challenge. The pain reaction during the total observation period was reduced by 57% (P < 0.005). The analgesic action induced by SMF was inhibited by subcutaneous administration of naloxone (1 and 0.2 mg kg(-1)), irreversible micro-opioid receptor antagonist beta-funaltrexamine (20 mg kg(-1)) and delta-opioid receptor antagonist naltrindole (0.5 mg kg(-1)), but the kappa-opioid receptor antagonist norbinaltorphimine (20 mg kg(-1)) failed to affect the SMF-induced antinociception. In contrast to the subcutaneous administration, the intracerebroventricularly injected naloxone (10 microg mouse(-1)) did not antagonize the antinociceptive effect of SMF. The results suggest that acute exposure of mice to static magnetic field results in an opioid-mediated analgesic action in the writhing test in the mouse. The antinociceptive effect is likely to be mediated by micro and (to a lesser extent) delta-opioid receptors.     

Intragastric administration of cyclo(Leu-Gly) inhibits the development of tolerance to the analgesic effect of morphine in the rat

The effect of intragastric administration of cyclo(Leu-Gly), a cyclic dipeptide derived from melanotropin release inhibiting factor (Pro-Leu-Gly-NH2), on the development of tolerance to the analgesic effect of morphine in the rat was determined. The tolerance to morphine in the rat was induced by subcutaneous implantation of four morphine pellets during a 3-day period. The rats which served as controls were implanted with placebo pellets. The analgesic response to a challenge dose of morphine was determined by the tail-flick test. The tail-flick latencies were determined before and then every 30 min for 180 min. The analgesic response was computed by determining the area under the time-response curve. Implantation of morphine pellets resulted in the development of tolerance as evidenced by decreased analgesic response to morphine in morphine pellet implanted rats as compared to placebo pellet implanted rats. Chronic intragastric administration of cyclo(Leu-Gly) (4 to 16 mg/kg) inhibited the development of tolerance to morphine. A dose of 8 mg/kg of cyclo(Leu-Gly) completely blocked the tolerance to morphine. The study provides for the first time evidence that intragastric administration of a cyclic peptide can inhibit the development of tolerance to morphine, and that effective neuropeptides and their analogs can be developed as potential drugs to inhibit opiate-induced tolerance.     

Antinociceptive activity of salsolinol (racemate, R(+)-, S(-)-enantiomers): evidence of a peripheral mechanism

The existence and the characteristics of the antinociceptive action of salsolinol (racemate) and its two R(+)- and S(-)-enantiomers were studied using different pain tests in mice. None of these drugs possessed a significant activity on the tests sensitive to central acting analgesics (hot-plate and tail-flick tests), either after systemic (i.p.) or central (i.c.v.) injections. However, injected i.p., they reduced the number of writhes induced by phenylbenzoquinone; the ED50 was 79 +/- 2, 73 +/- 2 and 61 +/- 2 mg/kg for racemate, R(+)- and S(-)-enantiomer respectively. This activity was not antagonized by naloxone. Moreover, racemate and S(-) reduced, only for the highest used active dose on the PBQ test (128 mg/kg, i.p.), the edema induced by an intraplantar injection of carrageenin. These results provide evidence of an analgesic activity independent of the endogenous opiate systems and involving a peripheral mechanism.     

Molecular docking and analgesic studies of Erythrina variegata?s derived phytochemicals with COX enzymes

Secondary metabolites from plants are a good source for the NSAID drug development. We studied the analgesic activity of ethanolic extract of Erythrina variegata L. (Fabaceae) followed by molecular docking analysis. The analgesic activity of Erythrina variegata L. is evaluated by various methods viz., acetic acid-induced writhing test, hot plate and tail immersion test. Subsequently, molecular docking analysis has been performed to identify compounds having activity against COX-1 and COX-2 enzymes by using GOLD docking fitness. The result of preliminary phytochemical screening revealed that the extract contains alkaloids and flavonoids. In analgesic activity tests, the extract at the doses of 50, 100 and 200 mg/kg body weight (b.w.) produced a increase in pain threshold in a dose dependent manner. In acetic acid induced writhing test, the inhibitory effect was similar to the reference drug diclofenac sodium. The extract showed 18.89% writhing inhibitory effect at the dose 200 mg/kg b.w., whereas diclofenac sodium showed 79.42% inhibition of writhing at a dose of 10 mg/kg b.w. The results of tail immersion and hot plate test also showed potential analgesic activity of the extract which is also comparable to the standard drug morphine (5 mg/kg b.w.). Docking studies shows that phaseollin of Erythrina variegata L. has the best fitness score against the COX-1 which is 56.64 and 59.63 for COX- 2 enzyme. Phaseollin of Erythrina variegata L. detected with significant fitness score and hydrogen bonding against COX-1 and COX-2 is reported for further validation.     

Partial reversal of behavioral action of the agonist D-Trp-6-LH-RH by naloxone in mice

The effects of the superactive agonist analog D-Trp-6-LH-RH were investigated in several neuropharmacological tests: inhibition of picrotoxin-induced seizures, open-field behavior, hot-plate and tail-flick tests, assessment of catalepsy and apomorphine-induced cage-climbing. In most tests, D-Trp-6-LH-RH was administered subcutaneously (sc.) at the dose of 100 micrograms/kg. The opiate involvement in the peptide action was checked by using naloxone HCl (NX) in a dose of 1 mg/kg intraperitoneally (ip.), with the exception of the analgesic tests where the dose was 0.5 mg/kg. The analog significantly suppressed the open-field parameters of ambulation, rearing and grooming; except for grooming, these actions were fully antagonized by NX. Similarly, NX pretreatment restored to the control levels the latencies of seizure parameters increased by D-Trp-6-LH-RH. The hot-plate latencies did not change after pretreatment with NX but the opiate antagonist was fully able to antagonize the analgesic effect of the peptide in the tail-flick test. The cataleptogenic effect and the inhibition of apomorphine-induced cage-climbing demonstrated after D-Trp-LH-RH were not antagonized by NX.     

Immobility response elicited by clamping the neck induces antinociception in a "tonic pain" test in mice

Clamping the neck followed by body inversion to a supine position in mice elicits an immobility response called immobility by clamping the neck (ICN). The noxious pinch to the scruff of the neck produces antinociception in "phasic pain" models (e.g. tail-flick test). Here, a "tonic pain" model was used to test the antinociception associated with the ICN, and naloxone was used to determine the role of opioids in such antinociception. Mice were injected intraperitoneally with 0.3 mL of 0.4% acetic acid to produce writhing responses that were measured for one hour. ICN was induced every five minutes for one hour. Naloxone (5 mg/kg ip) was injected 10 min before acetic acid administration. There was a control group, sham clamping (SCLA). These mice were handled and restricted every five minutes as in the ICN but without real clamping. The repetitive inductions of ICN were able to reduce the writhing behavior; this antinociception was blocked by the naloxone pretreatment. In the SCLA group antinociception was not observed. These findings indicate that as in the "phasic pain" model, ICN also was able to elicit antinociception in this "tonic pain" model, and such antinociception seems to be mediated by opioids.     

Potent analgesic activity of the enkephalin-like tetrapeptide H-Tyr-D-Ala-Gly-Phe-NH2.

The N-terminal tetrapeptide amide analog of enkephalin (H-Tyr-D-Ala-Gly-Phe-NH₂) is approximately equipotent with highly active pentapeptide analogs of enkephalin (and with morphine) in producing analgesia after either intracerebroventricular or intravenous administration. Smaller fragments exhibited diminished potency, but even the dipeptide (H-Tyr-D-Ala-NH₂) retained naloxone-reversible analgesic activity at high intraventricular doses. These findings suggest that while the dipeptide has full intrinsic activity, the tetrapeptide sequence may be a minimum structural requirement for potent analgesia.     

A tetrapeptide isolated from hamster embryo with central opiate properties on gastrointestinal motility but not on pain perception

The effects of centrally administered kentsin (H-Thr-Pro-Arg-Lys-OH) on intestinal motility and on pain perception were investigated in rats chronically equipped with lateral ventricle catheters. Intestinal motility was recorded electromyographically from electrodes placed on the duodeno-jejunum; analgesia was evaluated by the hot-plate and tail-flick tests. Kentsin (4.0 ug/kg), injected intracerebroventricularly (ICV) 2 hours after the beginning of a meal, restores the "fasted" i.e. the migrating myoelectric complex of intestinal motility, while a 5 times higher dose administered subcutaneously was inactive. The ICV effect of kentsin was blocked by previous ICV administration of naloxone (400 ug/kg). In contrast, kentsin administered ICV (40 ug/kg) or SC (200 ug/kg) did not affect significantly (P greater than 0.05) the time latency in the two analgesic tests during 90 minutes after its administration and did not significantly modify the analgesic effects of (D5-Ala2, Met5) enkephalinamide. We conclude that kentsin when centrally administered acts on opiate receptors to alter gastrointestinal motility but without effects on pain perception.     

活络效灵丹抗炎镇痛作用的实验研究

目的：研究活络效灵丹的抗炎、镇痛、消肿等药理作用,为该药的临床研究提供基础。方法：用二甲苯致小鼠耳肿胀法和角又莱胶致大鼠足肿胀法研究抗炎作用,用热板法和扭体法研究镇痛作用。结果：活络效灵丹能较好地抑制二甲苯引起的小鼠耳廓炎性肿胀和大鼠甲醛致足跖肿胀,能显著提高热板试验小鼠的痛阈,有效抑制冰醋酸引起的小鼠扭体反应次数。结论：活络效灵丹具有良好的抗炎、镇痛、消肿等作用。     

Applications of the hexanic fraction of Agave sisalana Perrine ex Engelm (Asparagaceae): control of inflammation and pain screening

The present study evaluated the anti-inflammatory and analgesic properties of Agave sisalana Perrine in classic models of inflammation and pain. The hexanic fraction of A. sisalana (HFAS) was obtained by acid hydrolysis followed by hexanic reflux. Anti-inflammatory properties were examined in three acute mouse models (xylene ear oedema, hind paw oedema and pleurisy) and a chronic mouse model (granuloma cotton pellet). The antinociceptive potential was evaluated in chemical (acetic-acid) and thermal (tail-flick and hot-plate test) models of pain. When given orally, HFAS (5, 10, 25 and 50 mg/kg) reduced ear oedema (p < 0.0001; 52%, 71%, 62% and 42%, respectively). HFAS also reduced hind paw oedema at doses of 10 mg/kg and 25 mg/kg (p < 0.05; 42% and 58%, respectively) and pleurisy at doses of 10 mg/kg and 25 mg/kg (41% and 50%, respectively). In a chronic model, HFAS reduced inflammation by 46% and 58% at doses of 10 mg/kg and 25 mg/kg, respectively. Moreover, this fraction showed analgesic properties against the abdominal writhing in an acetic acid model (at doses of 5-25 mg/kg) with inhibitory rates of 24%, 54% and 48%. The HFAS also showed an increased latency time in the hot-plate (23% and 28%) and tail-flick tests (61% and 66%) for the 25 mg/kg and 50 mg/kg doses, respectively. These results suggest that HFAS has anti-inflammatory and analgesic properties.