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Mechanism of Action of Beta Blockers

Mechanism of Action of Beta Blockers

Beta blockers are a class of prescription drugs that are used for the treatment of heart ailments and various other diseases such as hypertension, anxiety, and glaucoma. This write-up provides information on the mechanism of action of these drugs.
Smita Pandit
Last Updated: Feb 10, 2018
Beta blockers, which are also known as beta-adrenergic blocking agents or beta-adrenergic antagonists, are drugs that were initially used for treating hypertension and heart conditions such as cardiac arrhythmia and heart attack. Over the years, medical research has revealed their ability to alleviate the symptoms of other medical conditions such as atrial fibrillation, angina, accelerated heart rate, heart failure, anxiety, and glaucoma.
Beta-adrenergic Antagonists and Beta Receptors
The heterogeneous group of beta-adrenergic blocking agents are classified on the basis of the beta receptors they block. Beta receptors, which fall under the category of adrenergic receptors, are receptors that are found on the surface of cells of some organs or tissues. These are classified into beta-1, beta-2 and beta-3 receptors. Beta-1 receptors can be found in the eyes, kidneys, and the heart, whereas beta-2 receptors are located in the liver, lungs, blood vessels, smooth vascular muscles, and gastrointestinal tract. Beta-3 receptors can be found in the adipose tissue.
When these are targeted by adrenergic substances such as epinephrine or norepinephrine, certain physiologic responses take place. It is the stimulation of the beta-receptors by epinephrine and norepinephrine that gives rise to the flight or fight response. It is the stimulation of these receptors that cause an accelerated heart rate, rapid heartbeat, or increase in high blood pressure that is experienced when we feel intense fear. Beta-adrenergic blocking agents prevent norepinephrine and epinephrine from binding to these receptors, thereby preventing such physiologic responses.
How Do Beta-adrenergic Antagonists Work
The term 'mechanism of action' is used with reference to the specific biochemical interaction that helps a drug produce its pharmacological effect. Beta-adrenergic blocking agents work by blocking the beta-receptors, thereby preventing epinephrine and norepinephrine from binding to these beta receptors. Given below is some information on the ways in which these drugs help in the treatment of certain diseases.
Hypertension
The specific biochemical interaction of these drugs in hypertension is not very clear, but it is believed that blood pressure is lowered due to lowering of the cardiac output. In many cases, it has been observed that an increased blood volume and cardiac output raises the blood pressure. The effect of these drugs in the treatment of hypertension is attributed to a reduced cardiac output. Dilation of small arteries or blood vessels due to use of these drugs may also have an effect on blood pressure. It is also believed that these drugs affect the production of renin, thereby lowering the production of angiotensin-II, which is a substance that constricts the blood vessels. This causes an increase in blood pressure.
Heart Conditions
Cardioselective beta blockers have long been used for treating heart problems such as cardiac arrhythmia, angina, increased heart rate, and heart failure. The pharmacological effect of these drugs on people affected by angina, heart failure, or arrhythmia is again associated with the inability of norepinephrine and epinephrine to bind themselves to the beta-1 and beta-2 receptors present in the heart and blood vessels respectively. The use of these drugs limits the physiologic responses that exercise, stress, or such situations can have on the heart rate and force of contraction. Since the use of these drugs lowers the cardiac output or the amount of blood heart pumps out, the symptoms associated with these heart conditions are alleviated to a great extent. The lowering of the heart rate, force of contraction, and arterial pressure improves the cardiac function, which in turn reduces the possibility of a heart attack.
Glaucoma
Glaucoma is an eye condition that occurs when the intraocular pressure, which is the pressure exerted by the fluids in the eyeball, increases. This increase in eye pressure can cause damage to the optic nerve. This could give rise to blindness. To prevent a slow progression towards loss of vision, it is essential that the intraocular pressure be restored to normal. The stimulation of beta-2 receptors in the eyes can cause an increase in aqueous humor. Beta-adrenergic antagonists can prevent this response and help in decreasing production of aqueous humor, which in turn helps in stabilizing the intraocular pressure.
Beta blockers compete with epinephrine and norepinephrine for the receptor sites and prevent them from binding to these sites. Thus, all the physiological responses that result from the stimulation of receptors can be prevented. Besides the aforementioned medical conditions, these drugs are also being used for the treatment of migraine and anxiety.
The accelerated heart rate that is experienced due to nervousness and fear can be tackled with the use of these drugs. This is why performers who wish to prevent stage fright from affecting their performance might be recommended the use of these drugs. Though these drugs can help in alleviating the symptoms of serious diseases, one must watch out for side effects. These must always be taken under medical supervision.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.