Effect of chronic mineralocorticoid administration on calcium excretion in the rat

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Abstract
The effect of prolonged 9-alpha-fluorohydrocortisone administration on Na and Ca excretion was investigated in rats fed a low-Ca synthetic diet. In rats fed salt the administration of mineral-corticoid resulted in Na retention lasting 4 days after which Na excretion returned to control levels. The expansion of extracellular volume, occurring during the period of Na retention, was associated with 1- to 5-fold increase in Ca excretion that persisted even after Na balance was re-established. Omitting salt from the diet prevented the effect of mineralocorticoids on Ca excretion. Mineralocorticoids, by enhancing distal Na reabsorption, expand extracellular fluid volume, thereby suppressing Na and Ca reabsorption in the more proximal portions of the nephron.