Effects of acute administration of medetomidine on the behaviour, temperature and turnover rates of brain biogenic amines in rodents and reversal of these effects by atipamezole.

The effects of acute administration of medetomidine in rodents were examined. Low doses (2.5 micrograms/kg) were anxiolytic, higher doses (10-100 micrograms/kg) sedating, and above 100 micrograms/kg medetomidine treated rats lost their righting reflex and were hypothermic. These higher doses of medetomidine inhibited the release of noradrenaline (NA), dopamine and serotonin in the central nervous system, inhibition of NA release being the most sensitive to medetomidine. All the above effects could be antagonized by administration of suitable doses of the alpha 2-antagonist, atipamezole, indicating that the actions of medetomidine were mediated via activation of alpha 2-adrenoceptors.