The effect of prolonged treatment with oxyfedrine on intracellular potentials and on other features of cardiac function in rabbits and guinea-pigs.

1. Previous work in acute experiments has shown that the main pharmacological action of oxyfedrine is stimulation of beta-adrenoceptors, yet there have been clinical reports that the drug is beneficial in the treatment of angina pectoris.2. In the present experiments rabbits and guinea-pigs were treated for several weeks with daily i.p. injections of oxyfedrine.3. A daily dosage of 15 mg/kg oxyfedrine had no effect on growth rate for 4 weeks, but thereafter the growth rate of treated animals fell below that of controls.4. The heart weights of the treated animals, expressed as a percentage of body weight, were significantly lower than those of controls.5. Measurement of intracellular potentials in hearts taken from treated rabbits showed that the main effects were a reduction in the maximum rate of depolarization and a prolongation of the plateau of the action potential.6. Guinea-pigs treated for 6 weeks with 15 mg/kg oxyfedrine daily i.p. were protected to some extent from the toxic effect of ouabain infused intravenously.