Epinephrine differs from norepinephrine in its receptor selectivity profile. Which statement correctly describes this difference?

Explanation

## Epinephrine vs. Norepinephrine: Receptor Selectivity **Key Point:** The critical difference between epinephrine and norepinephrine lies in their β2-receptor affinity. Epinephrine has significant β2-agonist activity, whereas norepinephrine has minimal β2 effects. ### Receptor Binding Profile | Property | Epinephrine | Norepinephrine | | --- | --- | --- | | **α1-activity** | +++ | ++++ | | **α2-activity** | ++ | ++ | | **β1-activity** | +++ | +++ | | **β2-activity** | ++ | + (minimal) | | **Net effect** | Mixed α and β | Predominantly α | ### Clinical Consequences **Epinephrine:** - Causes β2-mediated bronchodilation and vasodilation in skeletal muscle - At low doses: β effects dominate → tachycardia, bronchodilation, decreased diastolic BP - At high doses: α effects dominate → vasoconstriction, increased systolic and diastolic BP **Norepinephrine:** - Minimal β2 activity → no significant bronchodilation - Predominantly α1 and β1 effects → vasoconstriction and increased cardiac output - Causes sustained increase in both systolic and diastolic BP with reflex bradycardia (due to α1-mediated vasoconstriction) **High-Yield:** Epinephrine is the drug of choice for anaphylaxis because its β2 effects cause bronchodilation and counteract the bronchoconstriction and angioedema of anaphylaxis. Norepinephrine would be ineffective for bronchodilation. **Mnemonic:** **EPI-β2** — Epinephrine has β2 activity; **NE-α** — Norepinephrine is predominantly α. [cite:KD Tripathi 8e Ch 11]