What effect does the release of EPO have on blood vessels?

• A. Vasodilation, decreased blood pressure
• B. Vasoconstriction, increased blood pressure
• C. No change in diameter
• D. Increased capillary permeability

Answer: (B)

EPO release raises the hematocrit by stimulating red blood cell production. More red cells make blood more viscous, which increases systemic vascular resistance. Because the heart must pump against this higher resistance, blood pressure goes up. In other words, the net vascular effect is an increase in resistance (a vasoconstriction-like outcome) and thus higher blood pressure. EPO’s main action is on erythroid precursors, not directly on sprouting or leaking vessels, so dilation, no change in diameter, or increased capillary permeability aren’t the typical consequences.