At moderate-dose epinephrine infusion (0.03-0.15 mcg/kg/min), which receptors are activated and how does SVR typically change?

At moderate-dose epinephrine infusion (0.03-0.15 mcg/kg/min), which receptors are activated and how does SVR typically change?

• A. Alpha and Beta; heart rate and contractility increase; SVR may increase or decrease (variable)
• B. Beta only; heart rate increases; SVR decreases
• C. Alpha only; heart rate decreases; SVR increases
• D. Alpha and Beta; heart rate decreases; SVR unchanged

Answer: (A)

Moderate-dose epinephrine engages both alpha-1 and beta receptors. The beta-1 effect increases heart rate and contractility, boosting cardiac output. In the vasculature, beta-2–mediated vasodilation can occur in some beds, while alpha-1–mediated vasoconstriction raises vascular tone. Because these actions oppose each other, the net change in systemic vascular resistance is variable: some patients experience an increase, others a decrease, or little change, depending on the balance of receptor effects in different vascular regions and individual sensitivity. This combination of alpha and beta activation with a heart rate/inotropy boost best fits the moderate-dose range. The other options imply receptor selectivity that isn’t present at this dose, or incorrect effects on heart rate or SVR.

Moderate-dose epinephrine engages both alpha-1 and beta receptors. The beta-1 effect increases heart rate and contractility, boosting cardiac output. In the vasculature, beta-2–mediated vasodilation can occur in some beds, while alpha-1–mediated vasoconstriction raises vascular tone. Because these actions oppose each other, the net change in systemic vascular resistance is variable: some patients experience an increase, others a decrease, or little change, depending on the balance of receptor effects in different vascular regions and individual sensitivity. This combination of alpha and beta activation with a heart rate/inotropy boost best fits the moderate-dose range. The other options imply receptor selectivity that isn’t present at this dose, or incorrect effects on heart rate or SVR.