title: The effects of the d- and l-optical isomers of propranolol on the ventricular fibrillation threshold.
abstract: 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 msec and the current was delivered during the vulnerable period to the right ventricle as a 120 msec train of 4 msec 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 greater than 420.8% change from control. In contrast, the d-isomer caused only a small increase in the ventricular fibrillation threshold with the maximum increase ranging between 14.0 and 65.2% change from control. The maximum increase in VFT for the racemic mixture of propranolol was 44.7 to greater than 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 we conclude that propranolol's action in increasing the ventricular fibrillation threshold is dependent on its beta-blocking effect.
mesh_terms: D000818:Animals; D004285:Dogs; D004560:Electricity; D005260:Female; D006352:Heart Ventricles / Q000187:drug effects*; D007536:Isomerism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D011433:Propranolol / Q000378:metabolism / Q000494:pharmacology*; D014693:Ventricular Fibrillation / Q000378:metabolism*
chemical_list: D011433:Propranolol; D007545:Isoproterenol