Effects of xylazole on heart rate and blood pressure in conscious dogs

Xylazole (Xyl) is an analogue of xylazine (Xyn) synthesized by Lanzhou Institute of Chinese Traditional Veterinary Medicine. The effects of Xyl on heart rate and blood pressure were studied in 5 conscious dogs. Xyl 1 mg/kg iv was similar to Xyn in producing bradycardia and an initial transient hypertension followed by a lasting hypotension which was less significant than Xyn. Yohimbine (0.1 and 0.3 mg/kg), an alpha 2-adrenoreceptor blocking agent, antagonized bradycardia and hypotension induced by Xyl. Tolazoline (3.3 mg/kg), a nonselective alpha-adrenoreceptor blocking agent, reversed the bradycardia and hypotensive effect. Prazosin (1 mg/kg), an alpha 1-adrenoreceptor blocking agent, did not change Xyl-induced bradycardia and hypotension. Atropine (20 micrograms/kg) not only antagonized Xyl-induced bradycardia but also changed from bradycardia to tachycardia, and greatly potentiated Xyl-induced hypertension for more than 30 min. The results suggested that Xyl-induced cardiovascular effects are similar to Xyn that mediated by alpha 2-adrenoreceptor.