Renal handling of calcium and phosphate during mineralocorticoid administration in normal subjects

The renal handling of calcium and phosphate in relationship to the renal handling of sodium was studied in 7 healthy male volunteers under steady state metabolic conditions during prolonged (10 days) mineralocorticoid treatment. Calcium excretion was reduced together with sodium excretion during the early phase of mineralocorticoid treatment, whereas it increased independent of sodium excretion following the escape. Phosphate excretion did not change throughout. These results suggest that when there is extracellular volume expansion without increase in sodium intake and/or excretion, there is a dissociation of calcium and sodium excretion, suggesting that extracellular volume can affect the renal tubular handling of calcium probably as a result of mechanism(s) operating in the distal nephron.