AJP - Heart and Circulatory Physiology, Vol 257, Issue 4 1156-H1164, Copyright © 1989 by American Physiological Society
Alpha-adrenergic effects on relative refractory period in Purkinje system of intact canine left ventricles
J. B. Martins and D. J. Wendt
Department of Internal Medicine, University of Iowa, Iowa City 52242.
To investigate the electrophysiological effects of alpha-agonists, we
studied 23 chloralose-anesthetized sinoaortic and vagotomized dogs,
measuring epicardial and endocardial effective refractory period and
relative refractory period of the Purkinje system during graded infusions
of norepinephrine and phenylephrine. In group 1, epicardial and endocardial
effective refractory periods shortened equivalently with norepinephrine.
These effects were blocked with metoprolol. In group 2, epicardial and
endocardial refractory periods did not prolong with phenylephrine despite
addition of metoprolol. In group 3, phenylephrine, after the addition of
metoprolol, prolonged the relative refractory period of Purkinje only at
the highest phenylephrine dose of 50 micrograms.kg-1.min-1. In group 4,
these latter effects were not produced by raising pressure with descending
aortic occlusion. However, the effects of phenylephrine were blocked with
prazosin (1.0 mg/kg). Taken together, these data demonstrate that
alpha-adrenergic influences prolong Purkinje but not muscle refractory
period in the intact canine ventricle. The high dose of phenylephrine and
resulting hypertension suggest that this may be a pharmacological and not a
physiological response.
