Effect of chronic mineralocorticoid administration on calcium excretion in the rat.

SUKI, WADI N., RICK S, SCHWETTMANN, FLOYD C. RECTOR, JR., AND DONALD W. SELDIN. &fect of chronic minerahorticoid administration on calcium excretion in the rat. Am. J. Ph ysiol. 2 15 ( 1) : 7 l-74. 1968.~The effect of prolonged 9-alphafluorohydrocortisone administration on sodium and calcium excretion was investigated in rats fed a low-calcium synthetic diet. In rats fed salt the administration of mineralocorticoid resulted in sodium retention lasting 4 days after which sodium excretion returned to control levels. The expansion of extracellular volume, occurring during the period of sodium retention, was associated with a twoto fivefold increase in calcium excretion that persisted even after sodium balance was re-established. Omitting salt from the diet prevented the effect of mineralocorticoids on calcium excretion. It was concluded that mineralocorticoids, by enhancing distal sodium reabsorption, expand extracellular fluid volume, thereby suppressing sodium as well as calcium reabsorption in the more proximal portions of the nephron.