Different toxicological profiles for various beta-blocking agents on cardiac function in isolated rat hearts

Area of Science:

• Pharmacology
• Cardiology
• Toxicology

Background:

• Beta-adrenergic receptor antagonists (beta-blockers) are widely used medications.
• Understanding their cardiotoxic properties is crucial for patient safety.
• Previous studies suggest varying cardiotoxicity among different beta-blockers.

Purpose of the Study:

• To compare the cardiotoxic effects of propranolol, timolol, and sotalol.
• To investigate the mechanisms underlying beta-blocker-induced cardiotoxicity, excluding beta-adrenergic receptor interference.
• To determine the influence of drug lipophilicity on cardiotoxic profiles.

Main Methods:

• Isolated, perfused rat hearts were used, with catecholamine depletion to isolate drug effects.
• Dose-dependent effects on myocardial contractility, stimulus formation, and conduction were assessed.
• Effects on coronary flow and threshold voltage were measured to assess local anesthetic properties.
• Ventricular pacing was employed to differentiate direct myocardial depression from heart rate-mediated effects.

Main Results:

• Propranolol and timolol induced dose-dependent decreases in contractility, stimulus formation, and conduction.
• Timolol's negative inotropic and conduction effects were not due to beta-adrenoceptor antagonism or membrane stabilization.
• Both propranolol and timolol reduced contractility directly, irrespective of heart rate changes.
• Sotalol exhibited only slight cardiodepressant activity at higher concentrations.

Conclusions:

• Beta-blocker cardiotoxicity may involve pharmacological properties beyond beta-adrenoceptor blockade or membrane stabilization.
• Direct myocardial depression contributes significantly to the cardiotoxic effects of propranolol and timolol.
• Drug lipophilicity appears to be a key determinant of the cardiotoxic profile within this drug class.