Carbonic anhydrase in the metanephrogenic zone of the human fetal kidney

The distribution of carbonic anhydrase in the metanephrogenic zone of the human fetal kidney was studied by the histochemical method of Hansson. In stage I nephrons (= renal vesicles) no or very little enzyme activity was found. Adjacent cortical collecting tubules, however, showed enzyme activity at the luminal cell surface. In stage II nephrons (= S-shaped tubules) the tubular cells displayed cytoplasmic carbonic anhydrase activity, while the glomeruli were inactive. Thus, the development of the nephron from stage I to stage II was accompanied by an increase in tubular cell carbonic anhydrase activity with partially another distribution than in the adult kidney. This may indicate an additional function of this enzyme in the developing nephron other than in the process of urinary acidification, e.g. to promote normal growth and differentiation of the tubular cells.