We have confirmed in a sensory blockade model that QX-314 is a local anesthetic with a slow onset and a long duration of reversible blockade. Capsaicin, a transient receptor potential vanilloid receptor agonist, accelerated QX-314's onset kinetics, whereas capsazepine, a transient receptor potential vanilloid receptor antagonist, decreased QX-314's efficacy. These observations raise the possibility that endovanilloids may modulate cell entry of QX-314.
Lumbar intrathecal QX-314 concentration-dependently produced irritation and death in mice, at lower concentrations than those associated with robust motor blockade. Although QX-314 did produce long-lasting neural blockade, these findings indicate that QX-314 is unlikely to be a suitable candidate for spinal anesthesia in humans.
Isovaline reduced responses in mouse pain models without producing acute toxicity, possibly by enhancing receptor modulation of nociceptive information.
Purpose The use of peripheral tramadol to block pain has been advocated. However, since its actions in the periphery have not been elucidated fully, we tested the hypothesis that peripheral tramadol blocks peripheral glutamate-induced nociceptive behaviour in mice. Methods First, we compared the duration of paw licking after intraplantar (ipl.) glutamate administration, with and without tramadol, using a randomized blinded controlled design. Next, we established the half maximal effective concentrations (EC 50s ) for local tramadol and reference compound lidocaine in the hot water tail-flick latency test and the glutamate-induced paw allodynia assay. Results Tramadol reduced glutamate-induced paw licking from 33 ± 12 sec to 4 ± 4 sec (mean ± SD; t test, P \ 0.05; n = 6 per group). The tramadol and lidocaine EC 50 nerve conduction blocks in the tail did not differ significantly (84 ± 24 mM vs 69 ± 5 mM, respectively).Although tramadol reduced glutamate-induced allodynia (EC 50 , 46 ± 13 mM), lidocaine was more potent (EC 50 , 13 ± 5 mM; Dixon's up-and-down method; P \ 0.05). Tramadol was 2.5 times as effective at blocking nerve conduction in the tail compared with allodynia in the paw. Conclusions Local tramadol administration blocked nociceptive behaviour in mice induced by peripheral glutamate. Compared with lidocaine, the relative potency of tramadol was lower for blocking glutamate-induced allodynia than for sensory nerve conduction blockade, suggesting the activation of a pronociceptive receptor system in the periphery.
RésuméObjectif L'utilisation de tramadol pe´riphe´rique a e´teṕ ropose´e pour bloquer la douleur. Cependant, comme nous ne connaissons pas pleinement ses actions sur les nerfs pe´riphe´riques, nous avons e´mis l'hypothe`se que le tramadol pe´riphe´rique bloquait les comportements nociceptifs provoque´s par le glutamate pe´riphe´rique chez la souris. Méthode Nous avons d'abord compare´la dure´e du le´chage de la patte apre`s une administration intraplantaire (ipl.) de glutamate, avec ou sans tramadol, en utilisant une me´thode contrôle´e randomise´e en aveugle. Ensuite, nous avons de´termine´les concentrations efficaces moyennes (CE 50 ) pour le tramadol administre´localement et un compose´de lidocaı¨ne comme re´fe´rence a`l'aide du test de latence du retrait de la queue et du test d'allodynie de la patte provoque´e par le glutamate. Résultats Le tramadol a re´duit le le´chage de patte provoque´par le glutamate de 33 ± 12 sec a`4 ± 4 sec (moyenne ± ET; test t, P \ 0,05; n = 6 par groupe). Les CE 50 pour le bloc de conduction nerveuse re´alise´avec le
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