Influence of yohimbine on xylazine-induced depression of central nervous, gastrointestinal and cardiovascular function in the calf.

The antagonistic effect of yohimbine HCl (0.25 mg/kg IV), and alpha 2-adrenergic antagonist, on xylazine (0.05 mg/kg IV)-induced depression of central nervous and cardiovascular activity and rumen motility was studied in post-weaning calves. Yohimbine, administered 3 min post-xylazine, significantly decreased the duration of rumen amotility (38.3 +/- 4.2 min versus 14.0 +/- 2.2 min). Sedation, however, as monitored by the duration of fetlock knuckling in calves suspended in a body sling, was not shortened by yohimbine treatment. Yohimbine alone produced a significant tachycardia and led to a reduction of the duration of xylazine-induced bradycardia. Our data indicate that yohimbine produces a significant reversal of xylazine-induced rumen hypomotility at dosage levels that are without effect on sedation induced by this drug.