Acting at b2 receptors on bronchial smooth muscle, Epi is a powerful bronchodilator, especially when bronchial muscle is contracted because of disease or in response to drugs or various auta-coids. Beneficial effects of Epi in asthma also may arise from b2-mediated inhibition of antigen-induced release of inflammatory mediators from mast cells, and to a lesser extent from an a adrenergic effect to diminish bronchial secretions and congestion within the mucosa. Other drugs, such as glucocorticoids and leukotriene-receptor antagonists, have more profound antiinflammatory effects in asthma (see Chapter 27).
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.