Effect of expansion of the extracellular space on the rate of urinary excretion of calcium

Abstract

The effect of expansion of the extracellular space on the rates of urinary excretion of Ca, Mg, K, and P, as well as Na, was examined in the dog. The extracellular space was expanded by the rapid infusion of isotonic solutions of NaCl. Depression of the filtrated loads of the ions during the period of expansion was assured by depression of the glomerular filtration rate (GFR) by inflating a balloon in the aorta superior to the renal arteries. The effects of variation in secretion of mineralocor-ticoid and antidiuretic hormone were minimized by supplying constant amounts of these substances through the experiment. The excretion rates as well as the clearances of only Ca and Na increased consistently and significantly during the period of expansion. A close correlation was found between the clearance of Ca and that of Na. A heightened rate of urinary Ca excretion is an integral part of the response of the kidney to expansion of the extracellular space.