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The effects of the dextro optical and levo optical isomers of propranolol on the ventricular fibrillation threshold

, : The effects of the dextro optical and levo optical isomers of propranolol on the ventricular fibrillation threshold. European Journal of Cardiology 7(2-3): 117-124

The minimum current required to induce ventricular fibrillation was determined in 22 sodium pentobarbital anesthetized open chest dogs in the presence of the d-or l-isomers of propranolol at concentrations of 0.2, 0.5 and 1.0 mg/kg. The hearts were paced from the right atrium at a constant basic cycle length of 350 ms and the current was delivered during the vulnerable period to the right ventricle as a 120 ms train of 4 ms square wave pulses at 100 Hz. The l-isomer of propranolol increased the ventricular fibrillation threshold (VFT) above control values at all concentrations; the maximum increase ranged from 17.8 to > 420.8% change from control. The d-isomer caused only a small increase in the ventricular fibrillation threshold with the maximum increase ranging between 14.0-65.2% change from control. The maximum increase in VFT for the racemic mixture of propranolol was 44.7 to > 500.0% above control and was similar to the l-isomer alone. Since the .beta.-blocking potency of the l-isomer is 100 times the potency of the d-isomer, apparently, propranolol's action in increasing the ventricular fibrillation threshold is dependent on its .beta.-blocking effect.


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