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

Abstract

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 attempted to clarify whether or not the noradrenaline release contributes to spinal analgesia by lidocaine. The effects of intrathecal injections of the alpha adrenoreceptor antagonists, prazosin (0.01-0.3 nmol) and yohimbine (0.1-3 nmol), on intrathecal 2% lidocaine were assessed using the tail-flick (TF) test in mice. Lidocaine significantly increased the TF latency for 15 min. Prazosin (0.03, 0.1 or 0.3 nmol) and yohimbine (0.3, 1.0 or 3.0 nmol) significantly reduced the lidocaine-induced increase of the TF latency 10 min after injection, although both drugs showed a ceiling effect. These results suggest that stimulation of the noradrenergic systems plays an important role in spinal analgesia by lidocaine.