title: Effect of amitraz on heart rate and aortic blood pressure in conscious dogs: influence of atropine, prazosin, tolazoline, and yohimbine.
abstract: The effect of amitraz on heart rate (HR) and mean aortic blood pressure (MAP) were studied in five conscious male dogs. An iv injection of amitraz (1 mg/kg) caused a decrease in HR, which was accompanied by sinus arrhythmia for at least 60 min. Administration of amitraz also caused an increase in MAP for 20 min. Atropine sulfate (0.045 mg/kg, iv) increased HR and prevented amitraz-induced bradycardia. In addition, atropine potentiated amitraz-induced hypertension for 45 min. Yohimbine, an alpha 2-adrenoreceptor antagonist, given iv at 0.1 mg/kg, prevented hypertension, bradycardia, and sinus arrhythmia induced by amitraz. Tolazoline, a nonselective alpha-adrenoreceptor antagonist, given iv at 5 mg/kg, reduced the bradycardia and sinus arrhythmia caused by amitraz administration but did not change amitraz-induced hypertension. Tolazoline alone also increased both HR and MAP. Prazosin, an alpha 1-adrenoreceptor antagonist, given iv at 1 mg/kg, did not affect the cardiovascular actions of amitraz. The results suggest that (1) alpha 2-adrenoreceptors mediate amitraz-induced bradycardia and hypertension, and (2) yohimbine, but not atropine, can be used to control the untoward reactions of amitraz.
mesh_terms: D000818:Animals; D001146:Arrhythmia, Sinus / Q000139:chemically induced / Q000517:prevention & control; D001285:Atropine / Q000627:therapeutic use*; D001794:Blood Pressure / Q000187:drug effects*; D001919:Bradycardia / Q000139:chemically induced / Q000517:prevention & control; D004285:Dogs; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects*; D007275:Injections, Intravenous; D008297:Male; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D014043:Tolazoline / Q000627:therapeutic use*; D014052:Toluidines; D015016:Yohimbine / Q000627:therapeutic use*
chemical_list: D011942:Receptors, Adrenergic, alpha; D014052:Toluidines; D015016:Yohimbine; C014983:amitraz; D001285:Atropine; D014043:Tolazoline