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Some beta blockers (e.g. oxprenolol, pindolol, penbutolol, labetalol and acebutolol) exhibit intrinsic sympathomimetic activity (ISA). These agents are capable of exerting low-level agonist activity at the β-adrenergic receptor while simultaneously acting as a receptor site antagonist .
The progress in β-blocker development led to the introduction of drugs with variety of properties. β-blockers were developed having a relative selectivity for cardiac β1-receptors (for example metoprolol and atenolol), partial adrenergic agonist activity , concomitant α-adrenergic blocking activity (for example labetalol and carvedilol) and ...
Beta-blockers with intrinsic sympathomimetic activity: acebutolol, pindolol; Some common side effects include increased airway resistance for non-selective beta-blockers, exacerbation of peripheral vascular diseases, and hypotension [15] Beta-blockers are contraindicated in patients with second- or third-degree atrioventricular block.
Stutterers also use beta blockers to avoid fight/flight responses, hence reducing the tendency to stutter. Since they promote a lower heart rate and reduce tremor, beta blockers have been used by some Olympic marksmen to enhance performance, though beta blockers are banned by the International Olympic Committee (IOC). [ 3 ]
Examples of sympathomimetic effects include increases in heart rate, force of cardiac contraction, and blood pressure. [1] The primary endogenous agonists of the sympathetic nervous system are the catecholamines (i.e., epinephrine [adrenaline], norepinephrine [noradrenaline], and dopamine ), which function as both neurotransmitters and hormones .
Acebutolol is a cardioselective beta-1 blocker which also considered a partial agonist due to its intrinsic sympathomimetic activity (ISA). This means it provides low-grade beta stimulation at rest but acting as typical beta-blockers when sympathetic activity is high. [3]
Labetalol is a beta blocker, or an antagonist of the β-adrenergic receptors. It is specifically a non-selective antagonist of the β 1-and β 2-adrenergic receptors. [17] Labetalol has intrinsic sympathomimetic activity. [17] It is also an antagonist of the α 1-adrenergic receptor, and hence is additionally an alpha blocker.
The combination of beta blockers and antihypertensive drugs will work on different mechanism to lower blood pressure. [17] For example, the co-administration of beta-1 blocker atenolol and ACE inhibitor lisinopril could produce a 50% larger reduction in blood pressure than using either drug alone. [18]