Mechanism of Action of Beta Blockers

Beta blockers (beta-adrenergic blocking agents or beta-adrenergic antagonists) are drugs which 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. In this article, we will look into the mechanism of action of beta blockers in the treatment of some of these diseases. Scroll down to find out how these drugs help in treating various medical conditions.

Connection between Beta Blockers 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. Beta-receptors are classified into beta-1, beta-2 and beta-3 receptors. Beta-1 receptors can be found in the eyes, kidneys and the heart and 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. An accelerated heart rate, rapid heartbeat or increase in high blood pressure that is experienced when we feel intense fear is caused due to the stimulation of beta-receptors. Since beta blockers prevent norepinephrine and epinephrine from binding to these receptors, such physiologic responses can be averted.

How Do Beta Blockers Work

The term 'mechanism of action' is used with reference to the specific biochemical interaction that helps a drug produce its pharmacological effect. Beta blockers 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 beta blockers help in the treatment of certain diseases.

Hypertension: Beta blockers were initially used for the treatment of high blood pressure. The specific biochemical interaction of beta blockers 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 seen that an increased blood volume as well as cardiac output raises the blood pressure. Thus, the effect of beta blockers 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 beta blockers affect the production of renin, thereby lowering the production of angiotensin-II, a substance known to narrow the blood vessels and thus, raise 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 beta blockers for people suffering from 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 beta blockers thus limit the physiologic responses that exercise, stress or such situations can have on the heart rate and force of contraction. Since the use of beta blockers 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. Beta blockers effects such as lowering of the heart rate, force of contraction and arterial pressure improves the cardiac function and thus, the possibility of one suffering from myocardial infarction or a heart attack is greatly reduced.

Glaucoma: These days, beta blockers are also being used for the treatment of an eye condition called glaucoma. Glaucoma 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. Since stimulation of beta-2 receptors in the eyes cause an increase in aqueous humor, use of beta blockers can prevent this response and help in decreasing production of aqueous humor. This will help in stabilizing the intraocular pressure.

The mechanism of action of beta blockers is associated with the blockage of beta-receptors by beta blockers. 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 stimulation of receptors can be prevented. Besides the aforementioned medical conditions, beta blockers 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.