Adaptive changes of H+ and/or bicarbonate transport in chronic metabolic acidosis: its quantitative evaluation by...

We have recently improved the technique of the isolated perfused rat kidney by addition of amino acids to the perfusion solution. Utilizing this improved preparation, we examined to what extent chronic acid-base status can alter H+ and/or bicarbonate transport in the whole kidney and the effect of acetazolamide (10(-4) M) on this process. Kidneys from rats that had been drinking tap water (control), 1.5% NH4Cl (acidotic), or 1.5% NaHCO3 (alkalotic) were perfused with a solution of identical pH and PCO2. During the control period, the fractional bicarbonate reabsorption was higher in acidotic rats than in control rats by 1.0% and urine pH was lower than those in control. On the other hand, the two parameters were not different between control and alkalotic rats. Acetazolamide increased urine pH and decreased the fractional bicarbonate reabsorption in all, but these parameters in acidotic and alkalotic rats were not different compared with those in control. We conclude that adaptive changes of H+ and/or bicarbonate transport in chronic metabolic acidosis corresponds to about 1.0% as fractional bicarbonate reabsorption by the isolated perfused kidney and is largely carbonic anhydrase dependent.