American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What effect does high-dose epinephrine primarily have on blood vessels?

1. Vasodilation

2. Vasodilation and smooth muscle relaxation

3. Vasoconstriction

4. No significant effect

The correct answer is: Vasoconstriction

High-dose epinephrine primarily exerts a vasoconstrictive effect on blood vessels due to its action on adrenergic receptors. Specifically, at high concentrations, epinephrine strongly activates alpha-1 adrenergic receptors located on vascular smooth muscle. This activation leads to increased intracellular calcium and subsequent contraction of the smooth muscle, resulting in vasoconstriction. Additionally, high doses of epinephrine can also have some effects on beta-2 adrenergic receptors, which are typically associated with vasodilation; however, the predominant action at high concentrations is on the alpha receptors, leading to a net effect of vasoconstriction. This is particularly evident in scenarios like anaphylaxis or cardiac arrest, where the administration of high-dose epinephrine is utilized to increase systemic vascular resistance and improve myocardial perfusion. Understanding the concentration-dependent effects of epinephrine is crucial, as lower doses can indeed produce vasodilation through beta-2 stimulation, but at high doses, the alpha-1 mediated vasoconstrictive effects will dominate. This reflects the complex pharmacodynamics of epinephrine and its clinical relevance in managing various acute medical situations.