Which statement about norepinephrine's effects on heart rate and blood pressure is true?

Which statement about norepinephrine's effects on heart rate and blood pressure is true?

• A. It always increases heart rate and decreases BP
• B. It increases BP with a consistently increased heart rate
• C. It has no effect on BP
• D. It increases BP with a variable heart rate response due to reflexes

Answer: (D)

Norepinephrine raises blood pressure primarily through alpha-1–mediated vasoconstriction, which increases systemic vascular resistance and mean arterial pressure. It also stimulates beta-1 receptors in the heart, promoting increased contractility and conduction, which can push the heart rate upward. But the rise in blood pressure triggers baroreceptor reflexes that tend to slow the heart via vagal mechanisms. The net heart rate response is therefore variable, depending on the balance between direct beta-1 stimulation and reflex-mediated changes, as well as dose and patient factors. That’s why the statement describing an increase in BP with a variable heart rate response due to reflexes is the best fit. The other options are inconsistent with norepinephrine’s strong vasoconstrictive effect and the reflex control of heart rate.

Norepinephrine raises blood pressure primarily through alpha-1–mediated vasoconstriction, which increases systemic vascular resistance and mean arterial pressure. It also stimulates beta-1 receptors in the heart, promoting increased contractility and conduction, which can push the heart rate upward. But the rise in blood pressure triggers baroreceptor reflexes that tend to slow the heart via vagal mechanisms. The net heart rate response is therefore variable, depending on the balance between direct beta-1 stimulation and reflex-mediated changes, as well as dose and patient factors. That’s why the statement describing an increase in BP with a variable heart rate response due to reflexes is the best fit. The other options are inconsistent with norepinephrine’s strong vasoconstrictive effect and the reflex control of heart rate.