Albuterol, used for asthma, primarily activates which receptor?

• A. Beta-1 adrenergic receptor
• B. M3 muscarinic receptor
• C. Beta-2 adrenergic receptor
• D. Alpha-1 adrenergic receptor

Answer: (C)

Albuterol acts primarily on beta-2 adrenergic receptors on bronchial smooth muscle. When these receptors are stimulated, they activate the Gs protein, which turns on adenylyl cyclase to raise cAMP levels. The elevated cAMP activates protein kinase A, leading to reduced intracellular calcium and relaxation of smooth muscle, producing bronchodilation. Higher cAMP also dampens mediator release from mast cells, helping prevent bronchoconstriction.

Choosing beta-1 adrenergic receptors would mainly affect the heart (increasing heart rate and contractility), which is not the desired bronchodilatory effect. Activating M3 muscarinic receptors would cause bronchoconstriction, not dilation. Alpha-1 receptors cause vasoconstriction, not bronchodilation. So the receptor albuterol primarily targets is the beta-2 adrenergic receptor.