EFFECT OF XYLAZINE ON HEART-RATE AND ARTERIAL BLOOD-PRESSURE IN CONSCIOUS DOGS, AS INFLUENCED BY ATROPINE, 4-AMINOPYRIDINE, DOXAPRAM, AND YOHIMBINE

  • 1 January 1985
    • journal article
    • research article
    • Vol. 186  (2) , 153-156
Abstract
The effects of xylazine on heart rate (HR) and mean arterial blood pressure (ABP) were studied in 5 conscious male dogs. An i.v. injection of xylazine (1 mg/kg) caused a decrease in HR, which was accompanied by sinus arrhythmia. Xylazine administration also caused an initial increase in ABP, which was followed by a decrease. Atropine sulfate (0.045 mg/kg, i.m.) increased both the ABP and HR, but prevented xylazine-induced bradycardia only in 3 of 5 dogs. The other 2 dogs had to be given a supplemental dose of atropine sulfate (0.01 mg/kg, i.v.) before xylazine-induced bradycardia was antagonized. In addition, atropine sulfate potentiated xylazine-induced hypertension for 60 min. Yohimbine, an .alpha.2-adrenoreceptor blocking agent, given i.v. at a dosage of 0.1 mg/kg, antagonized hypertension, hypotension and bradycardia induced by xylazine. In addition, doxapram HCl, given i.v. at a dosage of 5.5 mg/kg, antagonized bradycardia but potentiated xylazine-induced hypertension and an i.v. injection of 4-aminopyridine at a dosage of 0.5 mg/kg did not affect the cardiovascular actions of xylazine. Atropine sulfate at the i.m. dosage of 0.045 mg/kg may be insufficient to antagonize xylazine-induced bradycardia but may potentiate xylazine-induced hypertension; yohimbine may be useful in antagonizing these untoward reactions associated with xylazine administration. Doxapram and 4-aminopyridine were not found to be beneficial.

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