Effect of yohimbine on xylazine-induced prolongation of gastrointestinal transit in dogs.

The effect of xylazine on the transit of barium sulfate through the stomach and duodenum was evaluated in 4 dogs. Base-line transit time was determined while the dogs were nonsedated and undisturbed; the mean time for barium sulfate to move from the stomach to the duodenojejunal junction was 4.8 +/- 1.2 minutes. An IV injection of xylazine (1 mg/kg) prolonged the mean transit time to 157 +/- 37.8 minutes. During the xylazine-induced prolongation of gastrointestinal transit, there were no vigorous contractions for at least 90 minutes. Yohimbine, an alpha 2-adrenergic-blocking agent, given IV at a dosage of 0.1 mg/kg, did not affect gastrointestinal motility. It did, however, prevent both the gastrointestinal and sedative effects of xylazine. Atropine methylnitrate given IV at a dosage of 1 mg/kg prolonged the transit time to 13.8 +/- 2.4 minutes. After atropine methylnitrate injection, the gastrointestinal tract was more flaccid than with xylazine administration. The prolongation of transit induced by atropine methylnitrate was not prevented by yohimbine. It was concluded that gastrointestinal radiographic findings in animals under the influence of xylazine should be interpreted cautiously.