What is the primary action of albuterol in the lungs?

• A. Beta-2 receptor stimulation causing bronchodilation
• B. Alpha-1 receptor stimulation causing vasoconstriction
• C. Beta-1 receptor stimulation increasing heart rate
• D. Blockade of histamine receptors

Answer: (A)

Albuterol’s primary action in the lungs is stimulation of beta-2 adrenergic receptors on bronchial smooth muscle, which leads to bronchodilation. When these receptors are activated, a Gs protein signal increases cyclic AMP within the smooth muscle cells, triggering a cascade that reduces intracellular calcium and causes the muscle to relax. The result is widening of the airways and easier breathing, which is why albuterol is used as a fast-acting rescue inhaler in asthma and COPD.

This action is distinct from the other options: stimulating alpha-1 receptors would cause vasoconstriction, not bronchodilation; stimulating beta-1 receptors would primarily affect the heart (increasing heart rate and contractility) rather than the airways; and blocking histamine receptors would be an antihistamine effect, not a bronchodilatory mechanism. While some systemic absorption can cause mild cardiac effects, the intended and primary effect in the lungs is bronchodilation via beta-2 receptor activation.