The
sedative action of alpha 2-adrenergic agonists is generally ascribed to inhibition of the locus coeruleus (LC) and its ascending activating projection to the forebrain, although postsynaptic effects in the neocortex may also play a part. The
sedative effect of the drugs varies considerably between different species. Systemic application of alpha 2-adrenergic agents have
analgesic effects in addition to their
sedative actions. Descending noradrenergic projections from the LC area modulate
pain transmission at the spinal level. The purpose of this trial was to investigate the
sedative properties of
medetomidine in the cat.
Medetomidine was injected intramuscularly at dose rates of 0.02, 0.06 and 0.18 mg/kg.
Xylazine 3.0 mg/kg and saline were used for comparison.
Medetomidine increased drowsy waking at the expense of both arousal and sleep. Nociceptive reflexes were suppressed in the case of the smallest dose of
medetomidine, and abolished by the others. The 0.18 mg/kg dose of
medetomidine had approximately equal effect on vigilance as 3.0 mg/kg of
xylazine. The duration of the effect of
medetomidine was dose-dependent. The alpha-receptor blocker
phentolamine i.m. reversed the heavy sedation produced by
medetomidine.
Medetomidine also produced significant
bradycardia, but the duration of this effect was not dose-dependent.