Which alpha1-adrenergic agonist acts as a vasoconstrictor, nasal decongestant, and raises blood pressure?

Which alpha1-adrenergic agonist acts as a vasoconstrictor, nasal decongestant, and raises blood pressure?

• A. Norepinephrine
• B. Phenylephrine
• C. Isoproterenol
• D. Dobutamine

Answer: (B)

The question hooks onto the effects of activating alpha1-adrenergic receptors on vascular smooth muscle. Activation of alpha1 receptors causes constriction of arterioles and venous beds, which raises systemic vascular resistance and, in turn, blood pressure. In the nasal mucosa, this same vasoconstriction reduces swelling and nasal airway resistance, giving a decongestant effect. A drug that is selective for alpha1 receptors will primarily produce these vascular and nasal effects with less direct stimulation of the heart. Phenylephrine is the classic alpha1-selective agonist used for both vasoconstriction to raise BP and as a nasal decongestant. It can cause reflex bradycardia due to the blood pressure rise, but it lacks the beta effects that would increase heart rate or contractility. In contrast, norepinephrine has strong alpha1 effects but also beta1 activity (increasing heart rate and contractility), isoproterenol mainly stimulates beta receptors (causing vasodilation and BP drop), and dobutamine mainly stimulates beta1 (increasing cardiac output with less effect on vascular tone). Therefore phenylephrine best fits all three actions described.

The question hooks onto the effects of activating alpha1-adrenergic receptors on vascular smooth muscle. Activation of alpha1 receptors causes constriction of arterioles and venous beds, which raises systemic vascular resistance and, in turn, blood pressure. In the nasal mucosa, this same vasoconstriction reduces swelling and nasal airway resistance, giving a decongestant effect. A drug that is selective for alpha1 receptors will primarily produce these vascular and nasal effects with less direct stimulation of the heart. Phenylephrine is the classic alpha1-selective agonist used for both vasoconstriction to raise BP and as a nasal decongestant. It can cause reflex bradycardia due to the blood pressure rise, but it lacks the beta effects that would increase heart rate or contractility. In contrast, norepinephrine has strong alpha1 effects but also beta1 activity (increasing heart rate and contractility), isoproterenol mainly stimulates beta receptors (causing vasodilation and BP drop), and dobutamine mainly stimulates beta1 (increasing cardiac output with less effect on vascular tone). Therefore phenylephrine best fits all three actions described.