The action of norepinephrine at a sympathetic neuroeffector junction is terminated primarily by:

• A Enzymatic degradation by acetylcholinesterase in the synaptic cleft
• B Degradation by monoamine oxidase within the synaptic cleft
• C Diffusion into the bloodstream followed by hepatic glucuronidation
• D Reuptake into the presynaptic nerve terminal by a norepinephrine transporter ✓

Explanation

Unlike acetylcholine, which is destroyed in the cleft by acetylcholinesterase, norepinephrine is terminated chiefly by Uptake 1, active reuptake into the presynaptic terminal via the norepinephrine transporter. This is why cocaine and tricyclic antidepressants, which block this transporter, potentiate sympathetic effects. MAO and COMT act mainly intraneuronally or in the liver and contribute far less to rapid termination at the junction.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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