Norepinephrine: hormone and neurotransmitter in man

Area of Science:

• Physiology
• Endocrinology
• Neuroscience

Background:

• Norepinephrine is a key catecholamine involved in the sympathetic nervous system.
• Its role as both a neurotransmitter and a potential hormone is under investigation.

Purpose of the Study:

• To investigate the potential dual function of norepinephrine as a neurotransmitter and hormone.
• To determine the plasma concentrations required for norepinephrine to exert hormonal effects.

Main Methods:

• Controlled intravenous infusion of norepinephrine in healthy young men.
• Measurement of plasma norepinephrine concentrations, metabolic clearance, and production rates.
• Assessment of hemodynamic (blood pressure, heart rate) and metabolic (glucose, insulin, etc.) parameters.

Main Results:

• Norepinephrine exhibited a rapid plasma clearance with a half-time of approximately 2.4 minutes.
• Significant parabolic relationships were observed between plasma norepinephrine and various physiological markers.
• Hemodynamic and metabolic effects required plasma norepinephrine levels exceeding 1,800 pg/ml.

Conclusions:

• Under normal conditions, norepinephrine's biological actions are primarily attributed to its neurotransmitter function.
• During physiological stress (e.g., exercise, illness), norepinephrine levels can exceed 1,800 pg/ml.
• Elevated norepinephrine during stress may subserve a hormonal function in addition to its neurotransmitter role.