Postsynaptic alpha- and beta-adrenergic supersensitivity of recovery properties in the canine ventricle

Abstract

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.