Which physiologic response would you expect following administration of a drug that possesses alpha-1 (α1) properties?

• A. Peripheral Vasoconstriction
• B. Dilation of pupil
• C. Bronchodilation
• D. Decreased heart rate

Answer: (A)

Activation of alpha-1 adrenergic receptors on vascular smooth muscle causes the muscle to contract, leading to peripheral vasoconstriction. This receptor’s signaling is Gq-coupled, which triggers a cascade (PLC, IP3, DAG) that increases intracellular calcium and promotes smooth muscle contraction. The resulting constriction of arterioles raises systemic vascular resistance and blood pressure—the most characteristic physiological response you’d expect from an alpha-1–acting drug.

Pupil dilation is another alpha-1 effect, achieved by contraction of the iris radial muscle, so dilation of the pupil can occur as well. However, the primary systemic outcome clinicians look for with alpha-1 agonists is vasoconstriction.

Bronchodilation is driven mainly by beta-2 receptors; alpha-1 activation does not produce the beneficial bronchodilation associated with beta effects and, in some contexts, can even contribute to bronchoconstriction. Decreased heart rate is not a direct action of alpha-1 stimulation; reflex changes can occur with blood pressure shifts, but the direct and expected effect of alpha-1 activity is vasoconstriction.