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Circulating norepinephrine and cerebrovascular control in conscious humans
D S Kimmerly1, E Tutungi, T D Wilson
1Neurovascular Research Lab, University of Western Ontario, London, Ontario, Canada.
Clinical Physiology and Functional Imaging
|November 18, 2003
Summary
Alpha-adrenergic activation via norepinephrine (NE) did not directly constrict cerebral blood vessels. Instead, increased cerebral vascular resistance during NE infusion was an autoregulatory response to elevated blood pressure.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
Background:
- Cerebral vasoconstriction occurs during postural stress with elevated catecholamines.
- The role of alpha-adrenergic activation in cerebrovascular tone is not fully understood.
Purpose of the Study:
- To test if alpha-adrenergic activation directly affects cerebrovascular tone in healthy individuals.
- To investigate the effects of norepinephrine (NE) and phentolamine (PHO) on cerebral blood flow.
Main Methods:
- Measured mean arterial pressure (MAP) and middle cerebral artery blood flow velocity (MFV) in seven healthy individuals.
- Administered saline, NE (low and high doses), and NE with phentolamine (PHO).
Main Results:
- Norepinephrine (NE) increased MAP dose-dependently.
- MFV remained constant during NE infusions.
- Cerebral vascular resistance (CVR) increased with NE, attributed to autoregulation, not alpha-mediated constriction.
Conclusions:
- Alpha-adrenergic activation does not directly cause cerebral vasoconstriction.
- Increased CVR during NE infusion is an autoregulatory response to elevated blood pressure.
- Phentolamine (PHO) may interfere with normal blood pressure autoregulation.