title: Alteration in the arrhythmogenic dose of epinephrine (ADE) following xylazine administration to halothane-anesthetized dogs.
abstract: The arrhythmogenic dose of epinephrine (ADE) was determined in six dogs during halothane (1.35%) anesthesia before and after xylazine administration (1.1 mg/kg, i.v. bolus; 1.1 mg/kg/hr, i.v. infusion). The arrhythmogenic dose was determined by constant infusion of freshly mixed epinephrine (100 microgram/ml). The ADE was defined as the total dose of epinephrine which produced four or more intermittent or continuous premature ventricular contractions within a 15-sec period. Total dose was calculated as a function of infusion rate and time to arrhythmia. Following xylazine administration, ADE significantly decreased from 6.28 +/- 0.522 to 4.17 +/- 0.679 micrograms/kg. At the end of i.v. xylazine bolus administration, heart rate significantly decreased (115 +/- 4 to 99 +/- 4.9 b.p.m.), and mean arterial pressure significantly increased (83 +/- 4.0 to 122 +/- 3.4 mm Hg). Heart rate measured immediately prior to epinephrine-induced arrhythmia formation was significantly increased following xylazine administration (177 +/- 8 vs 78 +/- 3 b.p.m.). Mean arterial blood pressure was unchanged. Apparently, xylazine, a mixed alpha agonist, potentiated halothane-induced myocardial sensitization to ventricular arrhythmogenesis and was associated with a significant increase in heart rate, but not blood pressure, during subsequent epinephrine infusions.
mesh_terms: D000768:Anesthesia, General / Q000662:veterinary; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced / Q000662:veterinary*; D001794:Blood Pressure / Q000187:drug effects; D004283:Dog Diseases / Q000139:chemically induced*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004837:Epinephrine / Q000633:toxicity*; D005260:Female; D006221:Halothane; D007263:Infusions, Parenteral / Q000662:veterinary; D008297:Male; D014991:Xylazine
chemical_list: D014991:Xylazine; D006221:Halothane; D004837:Epinephrine