Which effect is produced by Beta-2 receptor activation?

• A. Bronchodilation
• B. Bronchoconstriction
• C. Vasoconstriction
• D. Decreased airway secretions

Answer: (A)

Activation of beta-2 receptors in the airway smooth muscle causes bronchodilation. When these receptors are stimulated, they couple to Gs proteins that activate adenylate cyclase, increasing cyclic AMP. Higher cAMP leads to activation of protein kinase A, which lowers intracellular calcium and relaxes the smooth muscle around the bronchi. The result is widened airways and easier airflow, which is why beta-2 agonists like albuterol are used to relieve bronchospasm in neonates and other patients. While beta-2 activation can modestly influence inflammatory mediator release from mast cells and may affect secretions, the defining and most immediate effect is bronchodilation. Bronchoconstriction would come from other pathways or receptor targets, not from beta-2 activation, and vasoconstriction is not the expected airway effect of beta-2 stimulation.