Protective effects of different beta-blocking agents against electroshock lethality in mice.

The protective effect of phenytoin against an electroshock lethal dose (ELD), was compared with that of three different beta-blocking agents. These compounds were propranolol with quinidine-like activity (QLA) but no intrinsic sympathomimetic activity (ISA), practolol with ISA but no QLA and metoprolol with no ISA but some QLA. Phenytoin (15 mg/kg) and propranolol (70 mg/kg) protected all the animals. Metoprolol was only effective at higher concentrations (130 mg/kg). Practolol afforded some degree of protection at low doses (20 mg/kg) but at higher doses its ISA can be deleterious by decreasing the ELD threshold. These results suggest that QLA is more important than beta-blocking activity for protection against electroshock lethality.