Beta blockers work by preventing the stress hormones epinephrine and norepinephrine from bonding with the adrenoceptors in the brain, heart, muscle tissues, eyes and vascular system. The hormones are a function of the body's sympathetic nervous system, which regulates the fight-or-flight response. If permitted to bond with the receptors, the stress hormones prepare the body by elevating the heart rate, raising blood pressure and dilating the pupils.
Hypertension
Beta blockers are commonly prescribed in patients with high blood pressure. The drugs reduce arterial pressure by reducing the overall output of the heart from systolic compression. They are most effective when taken by the patient over long periods rather than when they are prescribed to deal with an acute issue. As an added benefit, beta blockers inhibit the release of a chemical called renin from the kidneys, which allows for greater salt and water loss and thus leads to lower arterial pressure. High blood pressure caused by stress in high-risk individuals is reduced dramatically by blocking the sympathetic nervous system signals that elevate heart rate based on emotional stimuli.
Arrhythmias
Arrhythmia is a broad term applied to an abundance of electrical activity in the heart. This activity can lead to a rhythm that is too slow, too fast or irregular, as in the case of a heart murmur. Beta blockers regulate electrical activity by blocking the sympathetic nervous system's influence on electrical activity in the heart's natural pacemaker and reducing the conduction velocity.
Glaucoma
Beta blockers are a component of most major topical treatment drugs for glaucoma. Like the heart, liver and kidneys, the eyes have adrenoceptors that activate upon stimulation from the sympathetic nervous system in the form of stress hormones. These receptors inspire the over-production of aqueous humor, the liquid between the cornea and lens of the eye. Blocking that signal reduces pressure by inhibiting the production of aqueous humor.
Performance Anxiety
Based on studies conducted as far back as the mid-1970s, doctors readily prescribe beta blockers "off label," meaning for a purpose not explicitly stated in their original FDA approval, to combat performance anxiety or "stage fright." Since the body's fight-or-flight response is reliant upon the stress hormones' ability to bond with the adrenoceptors, blocking their ability to do so keeps otherwise jittery performers calm without the physiological effects of the body's insistent signal to flee.
