Ephedrine acts on adrenergic receptors primarily by which mechanism that distinguishes it from adrenaline?
- A Displacement of stored noradrenaline from nerve terminals (indirect action) plus weak direct agonism ✓
- B Direct agonism at alpha-1 and beta receptors only
- C Selective beta-2 agonism with no alpha activity
- D Inhibition of monoamine oxidase leading to increased catecholamine levels
Correct answer: A. Displacement of stored noradrenaline from nerve terminals (indirect action) plus weak direct agonism
Explanation
Ephedrine has a mixed mechanism: it displaces stored noradrenaline from sympathetic nerve terminals (indirect action) and has weak direct agonist activity at adrenoceptors. This indirect mechanism causes tachyphylaxis on repeated dosing as noradrenaline stores deplete. Adrenaline acts purely as a direct agonist. Ephedrine is not selective for beta-2 receptors and does not inhibit MAO.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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