Mechanism of hypercalciuria in experimental metabolic acidosis.

To study the mechanism of hypercalciuria in metabolic acidosis, ammonium chloride loading (long) test was performed in 68 stone formers and 50 controls. Administration of ammonium chloride in both stone formers and controls produced a significant increase in urinary volume, ammonium and calcium excretions, no change in plasma calcium and creatinine clearance and significant decrease in plasma bicarbonate. However, on the third day of ammonium chloride loading test, urinary ammonium excretion and plasma bicarbonate levels were significantly lower while urinary calcium excretion was significantly greater in stone formers than in controls. Thus calciuresis could be correlated with the degree of metabolic acidosis but not with the rate of urinary ammonium excretion.