Which of the following is not an action of epinephrine when administered intravenously in a high dose?
**Core Concept**
Epinephrine, when given intravenously in high dose, acts as a potent sympathomimetic agent, primarily activating α₁ and β₁ receptors. This leads to increased heart rate, blood pressure, and glycogenolysis in the liver. Its effects are central to the "fight-or-flight" response, including cardiac stimulation and bronchodilation.
**Why the Correct Answer is Right**
Epinephrine at high IV doses stimulates β₂ receptors in the lungs, resulting in **bronchodilation**, not bronchial constriction. The option stating "causes broachiolar constriction" is factually incorrect because epinephrine is a bronchodilator, not a bronchoconstrictor. The other options are well-documented: it increases liver glycogenolysis via glycogen phosphorylase activation, induces cardiac extrasystoles through β₁ stimulation, and causes restlessness and anxiety due to central nervous system excitation.
**Why Each Wrong Option is Incorrect**
Option A: Epinephrine potently stimulates glycogenolysis in the liver via β₂ and β₃ receptors, increasing blood glucose.
Option C: High-dose epinephrine causes tachycardia and arrhythmias, including extrasystoles, due to β₁ receptor overstimulation.
Option D: Central effects of epinephrine include restlessness and anxiety, mediated by stimulation of the limbic system and brainstem.
**Clinical Pearl / High-Yield Fact**
Remember: **Epinephrine causes bronchodilation, not bronchoconstriction** — this is a common exam trap. Always distinguish between α and β effects: α₁ → vasoconstriction, β₂ → bronchodilation.
✓ Correct Answer: B. Causes broachiolar constriction