Cerebrovascular responses to CO2 after inhibition of sympathetic activity.

The effects of inhalation of 10% CO2 in air on cerebral blood flow (CBF) and cerebrovascular resistance (CVR) were examined in 13 unanesthetized goats before and after impairment of the sympathetic activity present in cerebral vessels. Under control conditions, inhalation of CO2 increased CBF from 112 +/- 10.2 (SE) to 191 +/- 17.2 ml X min-1 X 100 g-1 and decreased CVR from 0.91 +/- 0.02 to 0.55 +/- 0.03 Torr X ml-1 X min X 100 g. After treatment with reserpine CO2 increased CBF to levels similar to those before treatment, but values for CVR were significantly lower. Inhalation of CO2 1-2 days after removal of both superior cervical sympathetic ganglia produced a larger increase in CBF and a greater drop in CVR, whereas at 6-20 days after ganglionectomy the effects of CO2 were analogous to those measured before the operation. The results suggest that the existence of an intact tonic adrenergic activity is a factor in the level of CVR achieved in hypercapnic acidosis.