What is the primary action of beta-agonists?

Beta-agonists primarily work by relaxing bronchial smooth muscle, which leads to bronchodilation. This action is particularly beneficial in conditions such as asthma and chronic obstructive pulmonary disease (COPD), where airway constriction is a major issue. By binding to beta-adrenergic receptors in the lungs, these medications induce smooth muscle relaxation, resulting in wider air passages and improved airflow. This mechanism effectively alleviates symptoms of wheezing, shortness of breath, and tightness in the chest associated with asthma and other respiratory conditions.

In contrast, other options describe actions that are not typical for beta-agonists. Blocking sodium channels refers to the mechanism of certain antiarrhythmic agents. Increasing mucus secretion is not a primary action of beta-agonists but rather a response to other factors in respiratory disease. Stimulating surfactant production relates more to neonatal respiratory distress syndrome treatments than to the pharmacological effects of beta-agonists. Thus, the focus on bronchodilation is what makes the correct answer stand out as the core function of beta-agonists.