Blockade of sympathetic activity causes a significant further increase in CBF during hypoxia.
..sympathetic activation exerts a significant protective action on CBF and blood-brain barrier (BBB) permeability (Bill and Lander 1976) an effect which is also seen in the presence of moderate increase increases in BP, where autoregulation maintains CBF almost constant.
The vasodilation which characterizes autoregulatory breakthrough is eliminated when the arterial baroreflex is interrupted (Talman et al. 1994), which suggests that it is an active process. It is possible that the breakthrough depends on release of nitric oxide or a NO donor associated with the removal of the sympathetic innervation of cerebral vessels (Talman and Dragon 1995).
Intoxications of the Nervous System
By Pierre J. Vinken, F. A. de Wolff, George W. Bruyn, Otto Appenzeller, Harold L. Klawans
Published by Elsevier Health Sciences, 1999
ISBN 0444828133, 9780444828132