ƒ ¿ - Adrenergic Blockade with Phenoxybenzamine Enhances Cerebrovascular CO 2 Reactivity

The influence of sympathetic nervous activity on cerebral circulation and cerebrovascular CO2 reactivity was investigated by an ƒ¿-adrenergic blockade with phenoxybenzamine (PBZ). Cerebral oxygen and carbon dioxide tension (BrPO2, BrPCO2) and arterial blood pressure were continuously recorded before, during and after intracarotid infusion of 5 mg/kg of PBZ. The effects of 5% CO2 inhalation were measured before and after the infusion of PBZ. Following the intracarotid infusion of PBZ, BrPO2 and BrPCO2 did not change significantly. After the ƒ¿-adrenergic blockade the degree of the increase in BrPO2 during 5% CO2 inhalation was significantly enhanced. The increase in the cerebrovascular CO2 reactivity produced by low dose PBZ suggests that the sympathetic nervous system modifies cerebrovascular CO2 reactivity. (Keio J Med 42 (2): 60-63, June 1993)