What type of receptor does phenylephrine primarily target?

Phenylephrine primarily targets the α1 adrenergic receptor, which is a subtype of adrenergic receptors that responds to catecholamines. When phenylephrine binds to α1 receptors, it leads to vasoconstriction of blood vessels, resulting in an increase in blood pressure. This action is particularly useful in clinical settings for the management of hypotension or to induce nasal decongestion through its effect on vascular smooth muscle.

The α1 receptor is G protein-coupled and operates through the phospholipase C pathway, leading to an increase in intracellular calcium levels and smooth muscle contraction. This mechanism explains why phenylephrine is often employed in cases where a rapid increase in vascular resistance is necessary.

Other receptors listed in the options, such as β1 and β2 receptors, primarily mediate different physiological responses. The β1 receptor is mainly involved in increasing heart rate and contractility, while the β2 receptor facilitates bronchodilation and vasodilation. The µ receptor is associated with opioid activity and pain modulation. Each of these receptors serves distinct functions that are not the primary focus of phenylephrine’s therapeutic effects. Thus, the choice of α1 receptor accurately reflects the drug's intended mechanism of action.