the Regulation of Cerebral

• Pharmacological blockade of the a adrenergic system by 20 mg phentolamine I.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. Additional Key Words sympathetic stimulation sympathetic blockade COL> reactivity cerebral circulation 13aXe intracarotid injection method CBF autoregulation • In a recent issue of this Journal Rosen-blum1 gave an extensive and critical review of the literature concerning neurogenic control of cerebral circulation. He came to the conclusion that anatomically a sympathetic innervation as far distal as minor arterioles is now beyond doubt, and he found increasing evidence of some kind of sympathetic control of the diameter of the intracerebral vessels. However, the data obtained by different investigators are conflicting and often difficult to interpret because of the numerous pitfalls in this research field, i.e., contamination with blood flow in the external carotid system, steady state problems, insufficient control with changes in blood gases (especially COn), changes in cerebral metabolism provoked by the experi-mental situation, impaired autoregulation due to the experimental procedure, inhomogeneous blood flow changes in different parts of th