Anti‐arrhythmic, local anaesthetic, and adrenergic blocking activity of some β‐receptor antagonists

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Abstract
1 The antagonistic effect of the β-receptor blocking compounds propranolol, Ph QA 33 and INPEA on ouabain-induced cardiac fibrillations in guinea-pigs was compared with their local anaesthetic and β-receptor blocking properties. 2 All three compounds were found capable of increasing the tolerance to ouabain and of reversing ouabain-induced fibrillations, the ED50 being 0.3 mg/kg intravenously, 0.5 mg/kg intravenously, and 1.5 mg/kg intravenously, respectively for propranolol, Ph QA 33 and INPEA. 3 Propranolol and Ph QA 33 were found to be moderate to strong local anaesthetics while INPEA had a considerably weaker though significant effect. 4 The order of potency as β-receptor blocking compounds was propranolol ≥ Ph QA 33 > INPEA, the latter compound being less than 1% as active as propranolol. 5 Despite the surprising finding that INPEA was effective against non-catecholamine-induced arrhythmias, the results support the general assumption that the anti-arrhythmic effect of β-receptor blocking compounds is related to their local anaesthetic action rather than to their β-blocking ability.