How do Beta Blockers Work?

Before we embark upon discussing how they work and what are they used for, let's understand what beta blockers are. Also known as beta-adrenergic antagonists, beta-adrenergic blocking agents and beta antagonists, beta blockers are a category of drugs and medications that are mostly used to treat abnormal electrical activity in the heart, preserve normal heart rhythm after a heart attack and for lowering high blood pressure. Therefore, as you must have inferred by now, this class of drugs is mostly used to treat conditions relating to abnormal cardiac activities and arterial pressure.

The name beta blockers comes from the modus operandi of these drugs which act by inhibiting the actions of the fight-or-flight stress hormones epinephrine and noradrenaline upon certain parts of the sympathetic nervous system, the 3 β-adrenergic receptors (β₁, β₂ and β₃), which deal with the fight-or-flight response and induce the various common stress related symptoms such as increased heart rate and dilated pupils. These receptors are present in all vital organs such as the heart, kidneys, liver, lungs and uterus, fat cells, the digestive tract and vascular as well as skeletal muscles.

A Brief Insight Into Beta Blockers' Course of Action

Now, when activated due to the action of the aforementioned stress hormones, the β₁ receptors, which are present in the heart and kidneys, increase the electrical conduction rate of the heart and induce the kidneys to produce renin which is an enzyme responsible for regulating the mean arterial pressure of the body when blood is pumped. This leads to cardiac arrhythmia and hypertension as a physiological indication of stress. By inhibiting the action of the β₁ receptors, beta blockers bring down the heart rate to normal and lower blood pressure, imparting an overall calming effect to the body.

When the β₂ receptors (which are located in the vascular smooth muscles, skeletal muscles, lungs, liver, uterus and digestive tract) are activated as a result of the action of stress hormones over them, it causes the smooth muscles to become relaxed and induce tremors to skeletal muscles and increase the rate of conversion of glycogen to glucose by the liver. Beta blockers inhibit these actions of the β₂ receptors and reduce tremors and glycogenolysis. They also dilate the blood vessels further and constrict the bronchi. They also inhibit the lipolytic actions of β₃ receptors by arresting the increased breakdown of lipids. The collective consequence of these various inhibitory actions manifest as decreased excitement, reduced physical exertion and an overall reduction of blood pressure which induces a calming, somewhat tranquilizing, effect.

What are Beta Blockers Used For?

As you can clearly infer from the previous segment, beta blockers are mainly used to arrest the symptoms of stress and anxiety which are brought on by the actions of certain stress hormones upon the three β-adrenergic receptors. On a more specific note, here's a list of uses of beta blockers for treating various clinical conditions:-

• High Blood Pressure
• Congestive Heart Failure
• Glaucoma
• Migraine
• Cardiac Arrhythmias
• Angina
• Essential Tremor
• Mitral Valve Prolapse
• Myocardial Infarction (heart attack)
• Various Anxiety Disorders
• Marfan Syndrome
• Pheochromocytoma (a neuroendocrine tumor which leads to excessive secretion of the stress hormone epinephrine)
• Aortic Dissection
• Abnormally Excessive Perspiration
• Post Traumatic Stress Disorder

Beta blockers can be selective as well as non selective, meaning they can either have a generic β-adrenergic receptor inhibiting action or can target any of the specific β-adrenergic receptors. Most beta blockers used for anxiety fall under the category of selective agents as they specifically target the β₁ receptors to reduce heart rate and lower mean arterial pressure. Also, since individuals suffering from anxiety disorders may frequently need to take beta blockers, selective agents are best as they do not interfere with any other organic functions and, therefore, leave lesser side effects than non-selective agents.