Effect of xylazine on heart rate and arterial blood pressure in conscious dogs, as influenced by atropine, 4-aminopyridine, doxapram, and yohimbine.
The effects of xylazine on heart rate (HR) and mean arterial blood pressure (ABP) were studied in 5 conscious male dogs. An IV 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, IM) 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, IV) before xylazine-induced bradycardia was antagonized. In addition, atropine sulfate potentiated xylazine-induced hypertension for 60 minutes. Yohimbine, an alpha 2-adrenoreceptor blocking agent, given IV at a dosage of 0.1 mg/kg, antagonized hypertension, hypotension, and bradycardia induced by xylazine. In addition, doxapram HCl, given IV at a dosage of 5.5 mg/kg, antagonized bradycardia but potentiated xylazine-induced hypertension, and an IV injection of 4-aminopyridine at a dosage of 0.5 mg/kg did not affect the cardiovascular actions of xylazine. It was concluded that atropine sulfate at the IM dosage of 0.045 mg/kg may be insufficient to antagonize xylazine-induced bradycardia but may potentiate xylazine-induced hypertension, and 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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D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004285:Dogs / Q000502:physiology*; D004315:Doxapram / Q000494:pharmacology*; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D013843:Thiazines / Q000494:pharmacology*; D014991:Xylazine / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology*
D000631:Aminopyridines; D000697:Central Nervous System Stimulants; D013843:Thiazines; D014991:Xylazine; D015016:Yohimbine; D001285:Atropine; D004315:Doxapram; D015761:4-Aminopyridine