Effects of alpha adrenoreceptor antagonists, prazosin and yohimbine, on intrathecal lidoeaine-induced antinociception in mice

Background: The precise mechanisms involved in the spinal analgesic effect of lidocaine are not yet clear. We previously found that lidocaine releases noradrenaline, a modulator of nociception, in rat spinal cord. Here, we at tempted to clarify whether or not the noradrenaline release contributes to spinal analgesia by lidocaine. Methods: The effects of intrathecal injections of the alpha adrenoreceptor antagonists, prazosin (0.01-0.3 nmol) and yohimbine (0.1-3 nmol), on intrat hecal 2% lidocaine were assessed using the tail-flick (TF) test in mice. Results: Lidocaine significantly increased the TF latency for 15 min. Prazo sin (0.03, 0.1 or 0.3 nmol) and yohimbine (0.3, 1.0 or 3.0 nmol) significan tly reduced the lidocaine-induced increase of the TF latency 10 min after i njection, although both drugs showed a ceiling effect. Conclusion: These results suggest that stimulation of the noradrenergic sys tems plays an important role in spinal analgesia by lidocaine.