Which adrenoceptor subtype mediates the presynaptic inhibition of norepinephrine release from sympathetic nerve terminals, acting as an autoreceptor?
- A Alpha-1A
- B Beta-2
- C Alpha-2A ✓
- D Alpha-1B
Correct answer: C. Alpha-2A
Explanation
Presynaptic alpha-2A autoreceptors on noradrenergic terminals are activated by released norepinephrine (NE), reducing further NE release via Gi-protein–mediated inhibition of adenylyl cyclase. This is a classic negative-feedback autoinhibition mechanism. Alpha-1 subtypes are postsynaptic; beta-2 presynaptic receptors actually facilitate NE release (positive modulation).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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