Abstract
The effects of a calcium antagonist, nifedipine, on the response of cerebral circulation to arterial Pco2 and arterial Pco2 changes were tested in 12 adult cats. Regional cerebral blood flow (rCBF) was measured using both hydrogen clearance method and heat clearance method in the thalamus, the frontal cotex and the deep white matter. Cerebrovascular reactivity to hypercapnia and hypoxemia was compared before and after intrarectal administration of nifedipine (1 mg/kg). Although resting rCBF values were significantly increased after nifedipine administration both in the gray matter and white matter, increment of rCBF during the inhalation of 5% CO2 in air or 10% O2 with 90% N2 was markedly reduced after nifedipine. These findings suggest that calcium antagonist may modulate the chemical control of cerebral circulation and that calcium ions may be involved in the chemical control as a final common path to the contraction of vascular smooth muscles. Furthermore, these findings may have significant implications for the therapeutic use of calcium antagonists in acute cerebrovascular accidents.
