Micropuncture study of bicarbonate reabsorption by the dog nephron

Abstract

Late proximal and distal tubular fluid samples were obtained by micropuncture techniques from dogs under the following conditions: normal acid-base balance, ammonium chloride acido-sis, metabolic alkalosis, and after acetazolamide administration. The pH and bicarbonate concentration of these samples were determined. During normal acid-base balance, bicarbonate reabsorption was proportional to volume reduction in the proximal tubule and acidification of tubular fluid was a function of the distal nephron. During acidosis, acidification occurred in the proximal tubule and significant bicarbonate reabsorption by the collecting duct was demonstrated. During metabolic alkalosis, the bicarbonate concentration was markedly higher in late proximal tubular fluid than in blood. In some of the normal dogs the bicarbonate concentration in urine was considerably higher than that in blood while distal tubular fluid bicarbonate concentration was consistently less than that in both blood and urine. Acetazolamide was found to inhibit bicarbonate reabsorption by the proximal tubule.