The effects of magnesium salts on the duration of epinephrine-induced ventricular tachyarrhythmias in anesthetized rats.

The effects of MgSO4 or MgCl2 infusion on the duration of epinephrine-induced cardiac arrhythmia were evaluated in male rats anesthetized with either halothane or pentobarbital. In addition, the duration of epinephrine-induced arrhythmia in pentobarbital (50 mg/kg) anesthetized rats was compared with the duration of arrhythmia in halothane (1.5%) anesthetized rats. During halothane anesthesia MgSO4 or MgCl2 infused at a dose rate of 8 mg.kg-1.min-1 for 20 min caused a significant reduction in the duration of arrhythmia (100% and 80%, respectively) following a 4-microgram/kg injection of epinephrine and a significant threefold reduction in arrhythmia duration for each salt following an 8- or 16-micrograms/kg injection of epinephrine. Significantly shorter periods of arrhythmia after each dose of epinephrine were seen in rats anesthetized with pentobarbital than were seen in rats anesthetized with halothane. No significant difference was seen between MgSO4 or MgCl2 infusions in any of these studies. Twenty-minute infusions of MgSO4 (8 mg.kg-1.min-1) were compared with propranolol (0.03 mg.kg-1.min-1) and verapamil (0.5 micrograms.kg-1.min-1) infusions on the duration of arrhythmia after epinephrine (8 micrograms/kg) injections in halothane anesthetized rats. MgSO4 and propranolol infusion caused a significant reduction in the duration of arrhythmia (81% and 70%, respectively). Verapamil infusion caused only a 48% reduction in arrhythmia duration. While there was no significant difference between MgSO4 or propranolol, both caused a significantly greater reduction in arrhythmia than verapamil. CaCl2 (0.15 mM.kg-1.min-1) infusion for 5 min caused a significant fivefold increase in the duration of arrhythmia during halothane anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)