Beta blockers are medications that block the binding of catecholamines to beta adrenergic receptors. Catecholamines are chemical compounds that are produced and secreted into the bloodstream by a part of the adrenal gland called the adrenal medulla. Catecholamines are also produced in the central nervous system and in clusters of nerves and special cells distributed throughout the body. The three main catecholamines that are active in tissues and organs throughout the body are called epinephrine, norepinephrine, and dopamine. Epinephrine is more commonly known as adrenaline. Catecholamines act by binding to special structures called adrenergic receptors that are located on the surface of different types of cells. When a catecholamine molecule binds to an adrenergic receptor, it triggers a message that is relayed throughout the cell. Different cells respond to these messages in different ways. There are two different types of adrenergic receptors that are identified as alpha receptors and beta receptors. Beta receptors are located in cells that are distributed throughout the muscle tissue and conduction system of the heart, the walls of blood vessels, and the airways in the lungs. When catecholamines bind to beta receptors, they trigger messages that accelerate the heart rate, promote forceful contractions of the heart muscle, increase blood flow through the muscles, and promote air flow in the lungs.
Beta blockers work by binding to beta receptors, blocking the binding of catecholamines and the activity that is normally triggered by that binding. Beta blockers are mostly used to treat cardiovascular disorders. They have proven to be very effective when used to treat hypertension and arrhythmias triggered by abnormal electrical signals in the muscle tissue and conduction system of the heart. Certain types of beta blockers may also be used to treat a disorder called congestive heart failure.
In the setting of Graves' disease, beta blockers may help to control symptoms related to exposure to excess levels of thyroid hormone. Over time, exposure to excess levels of thyroid hormone may increase the number of beta receptors present on the surface of different cells. In turn, increased numbers of beta receptors may amplify the messages that are triggered when catecholamines bind to adrenergic receptors. These combined effects may contribute to escalation of some of the more debilitating symptoms associated with thyrotoxicosis, including palpitations, tremulousness, anxiety, and insomnia. Treatment with beta blockers may help to alleviate many of these symptoms. Beta blockers can usually be started and continued while other measures are taken to evaluate and treat any underlying disorders that may have led to the development of thyrotoxicosis. Beta blockers are usually taken as oral medications. Preparations that are commonly used to treat patients with thyrotoxicosis include propranolol, atenolol, and metoprolol.