Cerebral vascular responses to physiological stimulation of sympathetic pathways in cats.

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Abstract
The effect of physiological activation of sympathetic pathways on cerebral blood flow (CBF) and integrity of the blood-brain barrier during hypertension was studied. Increased sympathetic activity was induced in anesthetized cats by sinoaortic deafferentation (SAD), resulting in acute, severe neurogenic hypertension. Sympathetic innervation of 1 cerebral hemisphere was interrupted by sectioning the superior cervical ganglion or the cervical sympathetic trunk. CBF was measured with microspheres and disruption of the blood-brain barrier was evaluated using Evans blue dye. Following SAD, mean arterial pressure increased abruptly from 142 .+-. 8 (mean .+-. SE) to 226 .+-. 9 mm Hg and total CBF increased from 31 .+-. 2 to 99 .+-. 15 ml/min per 100 g. Blood flow and extent of disruption of the blood-brain barrier were less in the innervated hemibrain than in the denervated hemibrain. The influence of sympathetic nerves was most pronounced in cortical gray matter: blood flow was 24 .+-. 4% less (P < 0.05) in the cortical gray matter of the innervated hemibrain 1 min following SAD. Studies were performed to determine whether physiological stimulation of sympathetic nerves constricts cerebral vessels during hemorrhagic hypotension in cats. During hypotension, blood flow was significantly lower in several regions of the innervated hemibrain than in the denervated hemibrain, but the effect was very small. Neural regulation of CBF occurs when sympathetic tone is augmented by physiological stimuli during acute hypertension and hypotension. The data represent the 1st demonstration of a reduction in CBF when sympathetic nerves are activated physiologically during acute severe hypertension.