Effect of Adrenergic Receptor Blockade with Yohimbin, Metroprolol or Prazosin on Arrhythmogenic Dose of Epinephrine in Xylazine-Kethamine Anesthetized Dogs


Abstract: The arrhythmias occurring and caused to death during the anaesthesia is generated endogenous release of epinephrine or norepinephrine. Therefore, the effects of yohimbine (alpa-2 blocker), prazosin (alpha-1 blocker), metoprolol (beta-1 blocker) on the arrhythogenic dose of epinephrine in 10 dogs anesthetized with xylazine and kethamine combination, were researched in this study. The infusion of epinephrine, 1 mg/ml/min; yohimbine, 0.125 mg/kg; prazosin, 0.1 mg/kg; metoprolol 0.5 mg/kg in dose were made intravenously. The dose of epinephrine produced ventricular premature contraction and ventricular tachycardia were determined as total dose of epinephrine in mg/kg, given until the time that arrhythmia appeared. Metoprolol and prazosin increased the arrhythmic dose of epinephrine significantly as compared with control group. But yohimbine decreased only the arrhythmic dose of epinephrine to produce ventricular tachnycardia, when it is compared with control. The average dose of epinephrine produced ventricular tachycardia were 0.1±0.09 mg/kg in control, 0.067±0.08 mg/kg in yohimbine, 0.213±0.06 mg/kg in metoprolol, 0.197±0.08 mg/kg in prazosin administered groups. Prazosin and metoprolol were found to be effective in similar manner on the arrhythmic dose of epinephrine. There was no significant difference in heart rate between control and drug administered groups. The length of anesthesia in animals given yohimbin was shorter than those given metoprolol or prazosin. The similar antiarrhythmic effect of metoprolol and prazosin suggest that this effect comes from their negative chronothropic and inotropic effect. In this condition, the general result is decreased oxygen consuming of myocardium. Thus, the increasing of myocardial oxygen consuming and resulted hypoxia due to that, is seemed to be main effect for production of the arrhythmias by epinephrine. As a result it is shown that the prazosin and metoprolol may be used in safe to prevent the lethal arrhythmias which may be induced during the xylazine -kethamine anesthesia. On the other hand, yohimbine may be used to evoke the animals in a shorter time during the anesthesia, but not as antiarrhythmic agents in clinics.

Keywords: Anesthesia, xylazine-kethamine, Adrenergic blocker, arrhythmias.

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