THE SITE OF ACIDIFICATION OF THE URINE IN THE DOG'S KIDNEY

Abstract

Damage to the proximal tubules of one kidney in the dog resulted in a decrease in the acidity of the urine excreted by the damaged kidney. When ferric ammonium citrate and sodium ferrocyanide were injected intravenously into dogs excreting urines of pH 5.0 or less, Prussian blue was formed at the brush borders of the cells of the proximal tubules indicating an acidity of pH 3.5 or less. Injected Töpfer's reagent (range pH 2.9 to 4.0), and tropaeolin 00 (range pH 1.9 to 2.4) were seen in their acid forms at the same site. When a carbonic anhydrase inhibitor was injected into the renal artery of one kidney the above phenomena were not observed. When the urine pH was greater than 6.0 no Prussian blue was formed and the indicators listed were in their alkaline forms. In these animals injected bromothymol blue and bromocresol purple were seen in the lumina of the tubules in shades indicating a pH above 7.0 in the proximal tubules and about 6.0 to 6.5 in the distal tubules. It seems evident that, when dogs are excreting markedly acid urines, hydrogen ions are secreted in high concentration at the brush borders of the proximal convoluted tubules. On the other hand when the acidity of the urine is slight, acidification of the urine appears to take place in the distal tubule.