Dexmedetomidine does not modify the neuromuscular blocking action of vecuronium in the anaesthetized rat

Dexmedetomidine is a new alpha 2 adrenergic agonist anaesthetic adjuvant. In animal studies, dexmedetomidine produced muscle flaccidity and prevented opioid-induced muscle rigidity, apparently via a central mechanism. The effect of dexmedetomidine on the neuromuscular junction or on non-depolarizing neuromuscular block during anaesthesia has not been reported. We have studied in the anaesthesized rat, the effects of dexmedetomidine on vecuronium-induced twitch depression. Wistar rats (n = 35) were anaesthetized and their lungs ventilated to maintain normocapnia. An infusion of vecuronium of 2.3 (SEM 0.1) micrograms kg-1 min-1 produced a stable twitch height (T1) depression of the tibial nerve of 53 (2)% of control in all groups. Rats were allocated randomly to receive either saline or dexmedetomidine 10, 30 or 100 micrograms kg-1 i.v. and T1 height was measured continuously for 60 min. Dexmedetomidine did not significantly affect T1 height during the first 30 min of infusion. At later times there were minor differences between groups. With cessation of the infusion of vecuronium, T1 height recovered rapidly to normal in all groups. These data suggest that the neuromuscular blocking properties of dexmedetomidine are unlikely to be produced by action at the neuromuscular junction.