title: Halothane-catecholamine arrhythmias in swine (Sus scrofa).
abstract: The arrhythmogenic dose of epinephrine (ADE) was determined in 6 pigs during steady-state anesthesia (1.5% halothane in O2) and steady-state anesthesia plus xylazine (1.1 mg X kg-1 X hr-1; IV infusion) and after either prazosin (alpha 1) or metoprolol (beta 1) adrenergic blockade during halothane-xylazine (H-X) anesthesia. A constant infusion (1, 2, 3, 5, and 10 micrograms X kg-1 X min-1) of freshly mixed epinephrine (100 micrograms X ml-1 in saline solution) was used to determine ADE. The ADE was defined as the total dose of epinephrine which produced 4 or more continuous or intermittent, premature, ventricular contractions within a 15-s period. The mean epinephrine total dose values during 1.5% halothane anesthesia, H-X anesthesia alone, or H-X anesthesia after either prazosin (0.1 mg X kg-1) or metoprolol (0.5 mg X kg-1) adrenergic blockade were 3.60 +/- 0.844, 2.68 +/- 0.402, 11.85 +/- 3.804, and 5.17 +/- 0.587 micrograms X kg-1, respectively. Xylazine administration did not significantly decrease ADE, although mean arterial pressure significantly increased. Prazosin administration significantly increased ADE and was associated with an increased heart rate and a decreased mean arterial pressure. We conclude that alpha 1-blockade with prazosin is more protective to epinephrine-induced arrhythmias in H-X-anesthetized pigs than is beta 1-blockade with metoprolol.
mesh_terms: D000758:Anesthesia / Q000662:veterinary; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced*; D001794:Blood Pressure / Q000187:drug effects; D004837:Epinephrine / Q000633:toxicity*; D005260:Female; D006221:Halothane; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D013552:Swine; D014991:Xylazine / Q000494:pharmacology
chemical_list: D014991:Xylazine; D008790:Metoprolol; D006221:Halothane; D011224:Prazosin; D004837:Epinephrine