• L M Plunkett and R L Tackett.
• J. Pharmacol. Exp. Ther. 1983 Dec 1; 227 (3): 683-6.

AbstractThe purpose of this study was to determine the role of alpha receptors in the inotropic and cardiotoxic actions of digoxin. Pentobarbital-anesthetized dogs were pretreated centrally with either prazosin, a selective alpha-1 antagonist, or yohimbine, a selective alpha-2 antagonist. Cardiac rhythm, blood pressure and contractile force were monitored during a 60-min period after pretreatment and during a continuous i.v. infusion of digoxin (2.5 micrograms/kg/min). Both agents, when administered into the lateral ventricle, produced depressant effects on hemodynamic parameters. Yohimbine (100 and 200 micrograms/kg i.c.v.) significantly increased the arrhythmogenic and lethal doses of digoxin in a dose-dependent manner. The protective effects of yohimbine (200 micrograms/kg) were not evident when the drug was given peripherally. Central alpha-1 blockade with prazosin increased the lethal dose of digoxin only at the largest dose (100 micrograms/kg i.c.v.) and its effects may be attributed to nonspecific central activity. BHT-933 (5 micrograms/kg i.c.v.), a selective alpha-2 agonist, enhanced the toxic effects of digoxin by decreasing both the arrhythmogenic and lethal dose of digoxin. These results suggest a central alpha-2 receptor mediation of the cardiotoxic actions of digoxin.

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