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Alpha-2 adrenergic transmission and human baroreflex regulation
Jens Tank1, Andre Diedrich, Elke Szczech
1Department of Nephrology and Hypertension, Franz-Volhard-Clinic, Medical Faculty of the Charité and HELIOS Klinikum, Berlin, Germany.
Hypertension (Dallas, Tex. : 1979)
|March 24, 2004
Summary
Clonidine, an alpha-2 adrenoceptor agonist, enhances baroreflex heart rate control via parasympathetic activation in humans. However, it reduces sympathetic vasomotor tone, potentially impairing baroreflex-mediated sympathetic withdrawal.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Pharmacology
Background:
- Central alpha-2 adrenoceptor stimulation is known to augment parasympathetic tone in mice.
- Understanding its effects in humans is crucial for cardiovascular health research.
Purpose of the Study:
- To investigate the impact of clonidine on autonomic vasomotor tone and baroreflex regulation in healthy young adults.
- To differentiate the effects of alpha-2 adrenoceptor stimulation on heart rate and vasomotor control.
Main Methods:
- Assessed heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity in 9 participants.
- Analyzed HR variability in time and frequency domains.
- Determined baroreflex sensitivity using phenylephrine and nitroprusside infusions with and without clonidine.
Main Results:
- Clonidine significantly reduced resting BP, muscle sympathetic nerve activity, and HR.
- Baroreflex heart rate curve was reset to lower HR values, with increased HR variability.
- Clonidine reduced resting sympathetic vasomotor tone and impaired baroreflex-mediated sympathetic withdrawal.
Conclusions:
- Alpha-2 adrenoceptor stimulation differentially affects baroreflex control of heart rate and vasomotor tone.
- Clonidine augments baroreflex-mediated bradycardia, likely through parasympathetic activation.
- This stimulation reduces sympathetic vasomotor tone, potentially altering baroreflex responsiveness.