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Beta Adrenergic Blocking Agents
Adrenaline is the most commonly recognized member of a group of drugs (catecholamines) which have potent stimulatory effects throughout the body.
Catecholamines stimulate the heart to beat harder and faster, increase the blood pressure, dilate bronchial tubes, dilate some blood vessels while contracting others, alter insulin secretion and sweat production, and contract muscles at the base of the urinary bladder. The varying effects of catecholamines occur because different types of chemical catecholamine receptors are present in different organs. Two distinct types of catecholamine receptors are recognized; alpha ( ) and beta ( ), and each group has several sub-groups.
Drugs that interfere with catecholamines varying effects work by blocking either the alpha or beta receptor sites, or both, and some may selectively block only one receptor subtype.
A large number of beta blockers are presently clinically available. Some are highly subtype selective ( 1 or 2) while others are non-selective. Some are able to get into brain tissue - others not, and some actually partially stimulate the beta receptor while simultaneously blocking them. Whether selective or not, beta blockers lower blood pressure, reduce heart rate, reduce cardiac energy requirements, reduce and control certain heart rhythm disturbances, and have been definitively proven to reduce death rates after heart attacks.
Commonly used cardiac selective ( 1) blockers include ToprolŪ XL (metoprolol), atenolol, betaxolol, bisoprolol, and esmolol. Commonly used non-selective beta blockers include propranolol, nadolol, carvedilol, sotolol, and timolol. Labetolol has combined non-selective beta and alpha blocking activity, while acebutolol and pindolol are beta blockers with some beta receptor stimulatory effect