AJP - Heart and Circulatory Physiology, Vol 258, Issue 5 1339-H1347, Copyright © 1990 by American Physiological Society
Postsynaptic alpha- and beta-adrenergic supersensitivity of recovery properties in the canine ventricle
K. J. Van Why, D. D. Lund and J. B. Martins
Department of Internal Medicine, University of Iowa Hospitals.
We studied postsynaptic manifestations of adrenergic supersensitivity in
the canine left ventricle (LV) regionally denervated by phenol in 14 dogs.
Measurements were performed from 17 to 23 days later under alpha-chloralose
anesthesia after sinoaortic denervation and vagotomy. After the sternum was
split, multipolar pacing and recording electrodes were placed in both
innervated and denervated LV. With isoproterenol infusion at 0.1, 1, and 10
micrograms/min, there was no change in activation times or pacing
threshold. However, supersensitivity was manifested by a parallel left
shift in the isoproterenol dose to effective refractory period (ERP)
response curve (greater than or equal to 5.7 ms) in the denervated
endocardium and epicardium compared with the respective innervated LV (P
less than 0.05). In addition, local repolarization in the denervated area
shortened more than the innervated area with isoproterenol infusion and
correlated (r = 0.56) with the change in ERP. Postsynaptic supersensitivity
of Purkinje to isoproterenol was also manifested by a parallel left shift
(greater than or equal to 10 ms) in the dose to relative refractory period
response curve in the denervated compared with the innervated area (P less
than 0.05). In addition, a greater prolongation of Purkinje refractoriness
was observed with phenylephrine only at 50 micrograms.kg-1.min-1. We
conclude that postsynaptic supersensitivity occurred with the beta-agonist
isoproterenol in both muscle and Purkinje. However, only Purkinje in the
denervated area demonstrated an enhanced response to the alpha-agonist
phenylephrine.
