[Changes in (a-ET) PCO2 produced by acetazolamide in red cells, not in plasma]

The changes in (a-ET) PCO2, concentration of acetazolamide and inhibition rate of carbonic anhydrase in blood were measured for 3 hours after administration of acetazolamide to anesthetized dogs, in order to find whether the changes in (a-ET) PCO2 was in response to the concentration of acetazolamide in red cells or plasma. 1. The increase in (a-ET) PCO2 was stable for 3 hours after administration of acetazolamide (5-30 mg/kg). 2. According to the concentration of acetazolamide measured by HPLC, the concentration in erythrocytes increased quickly but decreased more slowly than in plasma. The concentration of acetazolamide in erythrocytes became higher than in plasma after 3 hours. 3. The change in the inhibition rate of CA activity in red cells and in plasma paralleled to the concentration of acetazolamide in red cells and in plasma. 4. (a-ET) PCO2 levels could be raised by low CA activity inhibited by acetazolamide in red cells, not in plasma. 5. Remaining in higher concentration of acetazolamide in erythrocytes might be occurred by the reason that acetazolamide combines with protein, especially CA, in erythrocytes to be unable to pass through the erythrocytes membrane smoothly.