Enhancement of lidocaine-induced epidural anesthesia by deoxyaconitine in the rabbit

Aconiti tuber has been used in traditional Oriental medicine to alleviate pain. The antinociceptive property of aconiti tuber is due to the action of its extracted alkaloids such as deoxyaconitine. The purpose of this study was to investigate the effect of epidural deoxyaconitine on epidural lidocaine anesthesia.

Five adult rabbits were used. Three different combinations of drugs were injected into the epidural space, in the following order: first (combination A), 1.5 ml of 2% lidocaine; second (combination B), 1.5 ml of 2% lidocaine and 150 micro g deoxyaconitine; and third (combination C), 3 mg nor-binaltorphimine followed by 1.5 ml of 2% lidocaine and 150 micro g deoxyaconitine 30 min later. The latency of onset and the duration of three end-points (sensory loss in the tail, loss of weight-bearing ability, and flaccid paresis of hind limb) were measured.

Onset times for the three end-points were not changed by deoxyaconitine or by nor-binaltorphimine. The duration of sensory loss was 27.0 +/- 2.7 min, the duration of loss of weight-bearing ability was 33.0 +/- 2.7 min, and the duration of flaccid paresis was 21.0 +/- 4.2 min in the combination A group. In the combination B group, deoxyaconitine extended the time of sensory loss by 80%, the time of loss of weight-bearing by 50%, and that of flaccid paresis by 60% compared with the combination A group. In the combination C group, this phenomenon was partially antagonized by pretreatment with nor-binaltorphimine, a kappa-opioid antagonist.

Based on our observations, deoxyaconitine enhanced epidural lidocaine anesthesia in the rabbit, and this effect seemed to be partly mediated by kappa-opioid receptors.