Abstract

Ventricular arrhythmias were produced in the dog heart-lung peparation (HLP) by a cornbination of epinephrine, halothane and aortic pressure elevation. The cardiac irregularities were antagonized by pretreatment of the HLP with the beta adrenergic blocking agents, N-isopropyl-p-nitrophenylethanolamine (INPEA), pronethalol and 4-(2-isopropylamino-l-hydroxyethyl)methanesulfonanilide (MJ 1999), but were not affected by Pretreatment with the alpha adrenergic blocking agent, phenoxybenzamine. Ouabain-induced ventricular arhythrnias were antagonized by pronethalol but not by INPEA or MJ 1999 in the HLP. However, the doses of pronethalol needed to inhibit the ouabain-induced arrhythmias were higher than those needed to antagonize the cardiac actions of epinephrine. Adrenergically induced cardiac arrhythmias thus appear to be subserved by beta but not by alpha adrenergic receptors.