Ephedrine produces its pressor and bronchodilator effects primarily by which mechanism?
- A Direct stimulation of alpha-1 and beta-1 adrenergic receptors only
- B Indirect release of norepinephrine from sympathetic nerve terminals with some direct receptor stimulation ✓
- C Inhibition of norepinephrine reuptake at the norepinephrine transporter
- D Activation of dopamine D-1 receptors causing vasodilation and baroreflex-mediated tachycardia
Correct answer: B. Indirect release of norepinephrine from sympathetic nerve terminals with some direct receptor stimulation
Explanation
Ephedrine acts both directly on adrenergic receptors and indirectly by promoting norepinephrine release from presynaptic vesicles. This dual mechanism explains its tachyphylaxis with repeated dosing as norepinephrine stores deplete. It is not a pure reuptake inhibitor and its indirect component distinguishes it from pure direct agonists.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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