The sympathetic nervous system is a part of the nervous system that helps to regulate certain involuntary (autonomic) functions in the body such as the function of the heart and blood vessels. The nerves of the sympathetic nervous system extend throughout the body and exert their effects by releasing chemicals that travel to nearby cells in the body, for example, muscle cells. The released chemicals bind to receptors (molecules) on the surface of the nearby cells and stimulate or inhibit the function of the cells. In the heart and blood vessels, the receptors for the sympathetic nervous system that are most important are the beta receptors. When stimulated, beta-receptors in the heart increase the heart rate and the strength of heart contractions (pumping action). Beta-blocking drugs acting on the heart on these Beta receptors, therefore, slow the heart rate and reduce the force of the heart’s contraction.

Stimulation of beta-receptors in the smooth muscle of the peripheral arteries and in the airways of the lung causes these muscles to relax. Accordingly, beta-blockers cause contraction of the smooth muscle of the peripheral arteries and thereby decrease the blood flow to the tissues throughout the body. As a result, the patient may experience, for example, coolness in the hands and feet. Likewise, in response to the beta-blockers, the airways are squeezed (constricted) by the contracting smooth muscle. This squeezing (impingement) on the airway causes wheezing, especially in individuals with a tendency for asthma. So remember, Beta Blockers are contracindicated in Asthametic patients. In short, beta-blockers reduce both the force of the heart's pumping action and the blood pressure that the heart generates in the arteries.

Beta-blockers remain useful medications in treating hypertension, especially in patients with a fast heartbeat while resting (tachycardia), cardiac chest pain (angina), or a recent heart attack (myocardial infarction). For example, beta-blockers appear to improve long-term survival when given to patients who have had a heart attack. Whether beta-blockers can prevent heart problems (are cardio-protective) in patients with hypertension any more than other anti-hypertensive medications, however, is uncertain. Beta-blockers may be considered for treatment of hypertension because they also may treat co-existing medical problems. For example, beta-blockers can help treat chronic anxiety or migraine headaches in people with hypertension. The common side effects of these drugs include depression, fatigue, nightmares, sexual impotence in males, and increased wheezing in people with asthma. The beta-blockers include atenolol (Tenormin), propranolol (Inderal), metoprolol (Toprol, Mepressor, Merol), nadolol (Corgard), betaxolol (Kerlone), acebutolol (Sectral), pindolol (Visken), and bisoprolol (Zebeta).