The effects of dexketoprofen on duration of analgesia to a thermal stimulus when compared with a systemic control in a rat sciatic nerve block with levobupivacaine

Effects of dexmedetomidine and dexketoprofen on the conduction block of rat sciatic nerve

Dexmedetomidine is a selective α2-adrenoceptor agonist that is used because of its sedative, anxiolytic, and analgesic effects. Dexketoprofen, which is used as an analgesic, is a nonselective nonsteroidal anti-inflammatory drug (NSAID). The use of dexmedetomidine and dexketoprofen as adjuvants to local anesthetics for the peripheral nerve is gradually increasing. In this study, we aimed to investigate the effects of different doses of dexmedetomidine and dexketoprofen on conduction block of rat sciatic nerve. The isolated sciatic nerve from adult rats was transferred to a nerve chamber. The compound action potentials (CAPs) were recorded from stimulated nerve with electrophysiological methods. Dexmedetomidine (n = 8) and dexketoprofen (n = 8) were administered in the chamber with cumulative concentrations of 10-9 to 10-5 M, and the CAPs were recorded for 5 and 10 minutes. The CAP parameters were calculated. Both dexmedetomidine and dexketoprofen significantly depressed all CAP parameters in a dose-dependent manner compared with the control group, i.e., the group in which rats did not receive treatment. CAP parameters showed there was no significant difference in nerve conduction inhibition between dexmedetomidine and dexketoprofen. Higher doses of dexmedetomidine suppressed the conduction in the fast-conducting fibers; however, dexketoprofen was found to suppress the conduction in the slow-conducting fibers in a time-dependent manner and suppress the conduction in the medium- and slow-conducting fibers in a dose-dependent manner. These findings suggest that dexmedetomidine and dexketoprofen exhibit better anesthetic effects on peripheral nerve through different ways of action. The experimental procedures were approved by the Necmettin Erbakan University on January 30, 2013 (approval No. 2013-024).

Axonal excitability and conduction alterations caused by levobupivacaine in rat

In this study, effects of the long-acting amide-type local anesthetic levobupivacaine on axonal conduction and excitability parameters of the rat sciatic nerve were thoroughly examined both in vitro and in vivo. In order to deduce its effects on isolated nerve conduction, compound nerve action potential (CNAP) recordings were performed using the suction method over sciatic nerves of Wistar rats before and after administration of 0.05 % (1.7 mmol L-1) levobupivacaine. Levobupivacaine caused complete CNAP area and amplitude depression by blocking conduction in a time-dependent manner. To assess the influence of levobupivacaine on in vivo excitability properties, threshold-tracking (TT) protocols were performed at sciatic nerves of rats injected with perineural 0.05 % (1.7 mmol L-1) levobupivacaine or vehicle alone. Charge-duration TT results revealed that levobupivacaine increases the rheobase and decreases the strength-duration time constant, suggesting interference of the anesthetic with the opening of Na+ channels. Twenty and 40 % threshold electrotonus curves were found for both groups to follow the same paths, suggesting no significant effect of levobupivacaine on K+ channels for either the fastest or relatively slow conducting fibers. Current-threshold relationship results revealed no significant effect on axonal rectifying channels. However, according to the results of the recovery cycle protocol yielding the pattern of excitability changes following the impulse, potential deviation was found in the recovery characteristics of Na+ channels from the absolute refractory period. Consequently, conduction blockage caused by levobupivacaine may not be due to the passive (capacitive) properties of axon or the conductance of potassium channels but to the decrease in sodium channel conductance.