In vivo evidence that endogenous dopamine modulates sympathetic activity in man

Area of Science:

• Neuroendocrinology
• Autonomic Nervous System Physiology

Background:

• Dopamine D2-like receptor antagonists are known to influence the norepinephrine response to exercise.
• The precise role of endogenous dopamine in modulating sympathetic nerve activity in humans remains incompletely understood.

Purpose of the Study:

• To investigate the effect of domperidone, a D2-like antagonist, on norepinephrine response during physical exercise in Addison's disease patients.
• To assess the impact of domperidone on sympathovagal balance and heart rate variability in healthy volunteers.

Main Methods:

• Domperidone's effect on exercise-induced norepinephrine increase was studied in 6 Addison patients (3 adrenalectomized, 3 with adrenal tuberculosis) using placebo comparison.
• Sympathovagal balance was evaluated by heart rate variability (LF/HF ratio) in 9 normal volunteers after oral domperidone administration in supine and sitting positions.

Main Results:

• In Addison patients, domperidone significantly elevated norepinephrine levels during exercise compared to placebo (F=4.328; P<0.001).
• In healthy volunteers, domperidone increased the LF/HF ratio in the sitting position (P<0.05), indicating a shift in sympathovagal balance.
• Domperidone did not alter basal or stimulated norepinephrine plasma levels or blood pressure in normal volunteers.

Conclusions:

• Endogenous dopamine plays a role in regulating norepinephrine release from human sympathetic nerves in vivo.
• Dopamine D2-like receptor blockade influences autonomic nervous system regulation, particularly sympathetic outflow.