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Limited effect of systemic beta-blockade on sympathetic outflow
J Tank1, A Diedrich, C Schroeder
1Clinical Research Center, Helios-Kliniken, Franz Volhard Clinic and Max Delbrück Center for Molecular Medicine, Medical Faculty of the Charité, Humboldt University, Berlin, Germany. tank@fvk-berlin.de
Hypertension (Dallas, Tex. : 1979)
|December 26, 2001
Summary
Beta-blockade with propranolol did not decrease sympathetic activity in healthy individuals. Central beta-adrenoreceptors do not appear to tonically stimulate sympathetic outflow in young, normotensive subjects.
Area of Science:
- Cardiovascular Physiology
- Neuroscience
- Pharmacology
Background:
- Central beta-adrenoreceptors are hypothesized to augment sympathetic nervous system outflow.
- Beta-blockade is proposed to attenuate central sympathetic outflow by inhibiting these receptors.
Purpose of the Study:
- To test the hypothesis that beta-blockade inhibits central beta-adrenoreceptors, thereby attenuating central sympathetic outflow.
- To investigate the acute effects of propranolol on sympathetic activity and baroreflex function in healthy humans.
Main Methods:
- 18 healthy subjects received intravenous propranolol for complete beta-blockade.
- Continuous measurements included ECG, arterial blood pressure, and muscle sympathetic nerve activity.
- Baroreflex sensitivity was assessed using the sequence technique and pharmacological testing; cold pressor testing was also performed.
Main Results:
- Beta-blockade increased muscle sympathetic nerve activity (MSNA) but did not significantly alter blood pressure or baroreflex sensitivity.
- Heart rate response to cold pressor testing was blunted, but blood pressure and MSNA responses were similar to baseline.
- Operating points of baroreflexes during beta-blockade remained on baseline baroreflex curves.
Conclusions:
- Propranolol did not acutely decrease sympathetic activity in normotensive young subjects.
- The findings do not support a significant tonic stimulatory effect of central beta-adrenoreceptors on sympathetic outflow in this population.