Effects of adrenergic amines on electrophysiological properties and automaticity of neonatal and adult canine Purkinje fibers: evidence for alpha- and beta-adrenergic actions.

We determined age-related differences in automaticity and responsiveness of cardiac Purkinje fibers from adult and neonatal dogs to graded concentrations of epinephrine, isoproterenol, and phenylephrine. Purkinje fibers were studied with standard microelectrode techniques during superfusion with Tyrode's solution at 37 degrees C. Control spontaneous rates for adults and neonates did not differ significantly. There was a biphasic response to all agonists such that rate decreased at low and increased at high concentrations. The decrease was greater with phenylephrine and epinephrine than with isoproterenol. The increase in rate was greater with isoproterenol and epinephrine than with phenylephrine. Propranolol shifted the dose-response curves downward and to the right for all agonists; phentolamine, shifter the curves upward and to the left. Epinephrine and isoproterenol dose-response curves for the neonates were upward and to the left of those for adults. Phenylephrine curves were identical for adults and neonates. Thus there are alpha- and beta-adrenergic effects on Purkinje fiber automaticity; the former decrease and the latter increase rate. Furthermore, the effects on automiticity of beta-adrenergic amines are greater in the neonates than in the adult.