Antagonism of Medetomidine Sedation in Goats by Atipamezole and Yohimbine

Authors: MAHMOOD B. MAHMOOD, FOUAD K. MOHAMMAD

Abstract: The alpha 2-adrenoceptor antagonists atipamezole and yohimbine were used to antagonize medetomidine-induced sedation in 6-8-month-old native breed female goats. Intramuscular injection of medetomidine at the dose rate of 40 \mu g/kg body weight induced sedation and recumbency within 10-20 min in the goats. After recumbency, the goats were injected with saline (5 ml) (control group), atipamezole (0.2 mg/kg), or yohimbine (0.2 mg/kg) via the jugular vein. The duration of recumbency in the control group was 90 ± 9 min (mean ± SE). The effects of sedation continued in the control group goats even after regaining the righting reflex and standing. Atipamezole and yohimbine significantly reduced the recumbency period to 2 ± 1 and 45 ± 8 min, respectively, in comparison to the control group. The signs of arousal consisted of head raising, assuming sternal recumbency, and standing within 1 min in the atipamezole group and within 15-20 min in the yohimbine group. In contrast to the control group, the atipamezole- and yohimbine-treated goats appeared alert after standing. Atipamezole significantly, but partially reversed medetomidine-induced reductions in heart rate and ruminal contractions, whereas yohimbine partially reversed the medetomidine-induced decrease in heart rate only. The data suggest that atipamezole is useful for antagonizing the central nervous system depressant effects of medetomidine in goats. Atipamezole was also superior to yohimbine as a medetomidine antagonist.

Keywords: Alpha 2-antagonist, atipamezole, goat, medetomidine, yohimbine

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