The effect of acetazolamide on the changes of cerebral blood flow and oxygen metabolism during visual stimulation.

Acetazolamide, a carbonic anhydrase inhibitor, has an anticonvulsant effect which may result from a decrease in the efficacy of synaptic transmission due to a decrease of pH. Our previous study showed that acetazolamide induced a significant increase in global and regional cerebral blood flow (CBF), but caused no significant change in the cerebral metabolic rate of oxygen (CMRO(2)). To investigate the effect of acetazolamide on the responses of CBF and CMRO(2) during neural stimulation, we used positron emission tomography to measure CBF and CMRO(2) in six normal volunteers at the fixation-only baseline visual state and during visual stimulation before and after administration of 1 g of acetazolamide. Visual stimulation induced a significant increase in CBF (33%) in the visual cortex compared with baseline values, but caused no significant change in CMRO(2), while no significant change in global CBF or CMRO(2) was found. During visual stimulation after acetazolamide administration, both global and visual cortical CBF and CMRO(2) showed similar changes compared with the respective baseline values (37 and 65% increases in CBF and 8 and 16% decreases in CMRO(2), respectively). When corrected by the global values, the magnitudes of the CBF and CMRO(2) responses to visual stimulation after acetazolamide administration were less than those before (20% vs 38% in CBF and -9% vs 3% in CMRO(2)). Considering our previous observation that the effect of acetazolamide was similar throughout cerebral cortical regions, we suggest that acetazolamide decreases the responses of both CBF and CMRO(2) during visual stimulation, which indicates that this drug may affect neuronal excitability.