Effects of hypercalcemia on water and sodium excretion by the isolated dog kidney

The effects of acute hypercalcemia on hemodynamics and on water and sodium excretion were studied on the blood-perfused isolated dog kidney. This model advantageously eliminates various factors which modify medullary osmolality and intrarenal hemodynamics, as well as collecting duct permeability. Calcium ion directly inhibits sodium reabsorption in the proximal tubule and in the ascending limb of Henle's loop, leading to increased sodium excretion rate and to decreased free water generation. The vasoconstrictive action of calcium, leading to decreased glomerular filtration rate, may mitigate the strong natriuretic effect of this ion.