Vascular Effect of Epinephrine

Epinephrine is a:

Correct Answer: Both vasoconstrictor and vasodilator

Epinephrine (adrenaline) can act as both a vasoconstrictor and a vasodilator, depending on which adrenergic receptor it binds to.

Dual Action of Epinephrine

• α-adrenergic receptor activation: → Vasoconstriction (e.g., skin, viscera, mucous membranes)
• β₂-adrenergic receptor activation: → Vasodilation (e.g., skeletal muscle, coronary, pulmonary vessels)

Receptor Affinity

The affinity of epinephrine for β-receptors is greater than its affinity for α-receptors. So at low doses (pharmacological), vasodilation predominates; at high doses, vasoconstriction may be seen in peripheral vessels.

Physiological Context

During the 'fight or flight' response (epinephrine surge from adrenal medulla):

• Blood is shunted AWAY from skin and gut (α-vasoconstriction)
• Blood is shunted TOWARD skeletal muscles and heart (β-vasodilation)
• This optimizes oxygen delivery to working muscles during stress

Compare: Norepinephrine

Norepinephrine is predominantly a vasoconstrictor (strong α-agonist, weak β) — used clinically to raise blood pressure in shock. Epinephrine has much stronger β effects and is used in anaphylaxis (allergic shock).