The Sympathetic Nervous System and the Regulation of Cerebral Blood Flow in Man

Pharmacological blockade of the a adrenergic system by 20 mg phentolamine 1.V, was shown not to influence CBF in 14 patients with an intact cerebral autoregulation. If the autoregulation tested with angiotensin-was impaired for some reason, CBF was found to follow proportionally the blood pressure changes provoked by the blockade. The physiological sympathetic stimulation provoked by distention of the bladder did not alter the CBF (seven patients). The CO2 reactivity was unaffected by the sympathetic a blockade (six patients). It appears from these studies that the sympathetic system does not play any substantial role in regulation of CBF in man, and thus it would seem useless to try to influence the cerebral circulation for therapeutic purposes by systemic application of drugs, which directly or indirectly work via the sympathetic system.