Norepinephrine released from a sympathetic varicosity is removed from the synaptic cleft primarily by which mechanism, in contrast to acetylcholine?

• A Enzymatic destruction by monoamine oxidase within the cleft
• B Simple diffusion into blood, equally important for both transmitters
• C Active reuptake into the presynaptic nerve terminal ✓
• D Degradation by acetylcholinesterase at the junction

Explanation

Termination of noradrenergic signalling depends mainly on uptake-1, an active amine transporter (NET) on the presynaptic terminal that recaptures 70 to 90 percent of released norepinephrine; cocaine and tricyclics block this site. Acetylcholine has no equivalent reuptake and is terminated almost instantly by acetylcholinesterase hydrolysis in the cleft. MAO acts inside the terminal after reuptake, so option A misplaces the primary event.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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