The apparent buffer value of cerebrospinal fluid in acute hypercapnia.
Buffer mechanism of cerebrospinal fluid (CSF) against acute hypercapnia was studied in eighteen dogs. The dynamic response of CSF to a stepwise change of CO2 concentration in inspired gas (room air -- 6% CO2 -- 12% CO2) was observed in eleven dogs, maintaining each condition for two hours. The changes in CSF acidity were less than that in arterial blood, while increases of bicarbonate ion concentration [HCO3-] in CSF were more prominent. Apparent buffer values, delta[HCO3-]/deltapH, were calculated from the results in different levels of CO2 breathing : they were 22.7 slykes from room air to 6% CO2 (step 1), and 39.7 slykes from 6% to 12% CO2 (step 2). Similar experiments were performed in seven dogs, suppressing carbonic anhydrase activity by systemic administration of acetazolamide. Apparent buffer values of CSF were 14.4 slykes in step 1 and 16.0 slykes in step 2. From the result we conclude : 1) that the activity of buffer mechanism of CSF in respiratory acidosis is PCO2 dependent and becomes stronger when PCO2 of CSF increases ; 2) for the explanation of this characteristic buffer mechanism of CSF, participation of carbonic anhydrase is suggested for transport mechanism of bicarbonate ion into CSF.
D000086:Acetazolamide / Q000494:pharmacology; D000136:Acid-Base Equilibrium; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000134:cerebrospinal fluid; D002256:Carbonic Anhydrases / Q000378:metabolism / Q000502:physiology*; D003864:Depression, Chemical; D004285:Dogs; D006935:Hypercapnia / Q000134:cerebrospinal fluid*
D001639:Bicarbonates; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases; D000086:Acetazolamide