Effect Of Different Doses Of Atipamezole On Reversal Of Medetomidine-Induced Tear-Flow Decrease In Rats

It has been reported that alpha(2)-adrenoceptor agonists such as medetomidine decrease tear flow in many species, including rats. Few studies have investigated the involvement of alpha(2)-adrenoceptor in decreased tear flow; the issue has not been illustrated sufficiently. Therefore, we aimed to investigate the effect of different doses of atipamezole on the reversal of medetomidine-induced tear-flow decrease to reveal the specific involvement of alpha(2)-adrenoceptor. Treatment with 400, 800, or 1600 mu g/kg atipamezole (or saline as the control) was intramuscularly administered to rats 15 min following intramuscular administration of 200 mu g/kg medetomidine. After medetomidine administration, tear flow was measured using a phenol red thread test (PRTT). PRTT values decreased significantly after 200 mu g/kg medetomidine administration. The PRTT values after 800 (optimal dose to reverse) and 1600 mu g/kg atipamezole administration reached baseline, but never exceeded it significantly. Treatment with 400 mu g/kg atipamezole also reversed the decrease in PRTT value but the PRTT remained lower than baseline. The optimal dose and the higher dose of atipamezole fully reversed the medetomidine-induced decrease in tear flow to the baseline level in rats, while the lower dose of atipamezole partially recovered tear flow.