CHARACTERISTICS OF RENAL BICARBONATE REABSORPTION IN MAN*

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Abstract
The pattern of renal HCO3 reabsorption during various alterations in acid-base balance was examined in 13 normal subjects with and without the administration of Diamox (acetazoleamide): Following the administration of Diamox HCO3 reabsorption varied linearly with plasma PCO2, as described by the regression equation Y = 0.61 + 0.028 X. This linear relationship in the presence of marked inhibition of carbonic anhydrase indicated that the uncatalyzed hydration of CO2 was an important source of H+ for the reabsorption of HCO3. The failure of Diamox to produce marked HCO3 diuresis during metabolic acidosis was attributable to nearly complete reabsorption of the small filtered load via the uncatalyzed hydration of CO2. In vitro studies, in which varying amounts of HC1 Were added to phosphate-buffered HCO3 solutions, disclosed that the linear relationship between the reciprocals of HCO3 reabsorption and plasma HCO3, used as evidence for the active reabsorption of HCO3, was equally compatible with the theory that HCO3 is reabsorbed as the passive consequence of the secretion of H+.