What is the first step in termination of norepinephrine actions at the receptor?

What is the first step in termination of norepinephrine actions at the receptor?

• A. Metabolism by MAO in the synaptic cleft
• B. Reuptake into the nerve terminal
• C. Metabolism by COMT in plasma
• D. Diffusion away from the receptor

Answer: (D)

The correct answer focuses on the initial phase of terminating norepinephrine's effects at the receptor site, which begins with the diffusion of norepinephrine away from the receptor. Once norepinephrine has been released into the synaptic cleft, it binds to adrenergic receptors to exert its physiological effects. For these effects to stop, the molecule must first disengage from the receptor, which occurs mainly through diffusion. After this initial diffusion, other processes come into play, such as reuptake into the nerve terminal, where norepinephrine can be repackaged or metabolized, and enzymatic breakdown through monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT). However, the very first action that takes place in the termination process is that norepinephrine moves away from its receptor site, which sets the stage for its subsequent clearance from the synaptic space.

The correct answer focuses on the initial phase of terminating norepinephrine's effects at the receptor site, which begins with the diffusion of norepinephrine away from the receptor. Once norepinephrine has been released into the synaptic cleft, it binds to adrenergic receptors to exert its physiological effects. For these effects to stop, the molecule must first disengage from the receptor, which occurs mainly through diffusion.

After this initial diffusion, other processes come into play, such as reuptake into the nerve terminal, where norepinephrine can be repackaged or metabolized, and enzymatic breakdown through monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT). However, the very first action that takes place in the termination process is that norepinephrine moves away from its receptor site, which sets the stage for its subsequent clearance from the synaptic space.