Intrinsic sympathomimetic activity of?-adrenoceptor blocking agents

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Abstract
The pharmacological methods used to assess the intrinsic sympathomimetic activity (ISA) of β-blockers are discussed. The clinical relevance of ISA to respiratory function, peripheral resistance and cardiac function is reviewed. It appears doubtful whether ISA is always of predominant clinical significance and an alternative explanation is offered for many clinical effects observed with certain β-blockers, e.g. pindolol, oxprenolol, tolamolol, metoprolol, etc. Some effects of these β-blockers resemble those of labetalol, a new drug with both α- and β-blocking activity. Some clinical effects of certain β-blockers are more likely to be due to α-blocking activity than to their ISA.