Cardiac effects of beta-adrenergic receptor antagonists: beta-moderators versus beta-blockers

Two adrenergic receptor antagonists, acebutolol and propranolol, were observed to depress rabbit heart contractile force and adrenaline-stimulated adenylate cyclase activity at 1 X 10-(5) to 1 X 10-(3) M and 1 X 10-(6) to 1 X 10-(3) M concentrations, respectively. Acebutolol depressed sarcoplasmic reticular and mitochondrial calcium uptake at 5 X 10-(3) to 10-(2) M concentrations. On the other hand, propranolol was found to decrease calcium uptake activities of sarcoplasmic reticular and mitochondrial fractions at 1 X 10-(4) to 1 X 10-(2) M and 1 X 10-(3) to 1 X 10-(2) M concentrations, respectively. On the basis of these results with calcium transport systems, it is proposed that beta-antagonists with a mild depressant effect, such as acebutolol, may be called beta-moderators, whereas those with a strong effect, such as propranolol, may be called beta-blockers.