Reversal of medetomidine sedation in sheep by atipamezole and yohimbine.

The antagonistic effect of the alpha 2-adrenoceptor antagonists atipamezole and yohimbine on medetomidine-induced sedation was studied in male Awassi sheep. The animals were sedated with an im injection of 40 micrograms medetomidine/kg bw. After recumbency, the sheep were injected iv with either 5 ml physiological saline solution (control), 0.2 mg atipamezole/kg or 0.2 mg yohimbine/kg. The saline-treated animals remained sedated and recumbent for 61.3 +/- 3.0 (mean +/- SE) min. Atipamezole or yohimbine significantly reduced the recumbency period to 2.8 +/- 0.9 or 4.3 +/- 0.9 min, respectively. Atipamezole or yohimbine significantly increased the medetomidine-induced reductions in the heart rate, respiratory rate and ruminal contractions. Rectal temperature was neither affected by medetomidine nor by the subsequent administrations of antagonists. These data suggest the usefulness of atipamezole or yohimbine in antagonizing the sedative effects of medetomidine in sheep.