ON THE MECHANISM OF IMPAIRMENT OF RENAL CONCENTRATING ABILITY IN HYPERCALCEMIA*

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Abstract
The mechanism of hyposthenuria in hypercalcemia was investigated by analyzing renal tissue from rats intoxicated with vitamin D. Vitamin D intoxication produced a significant fall in the content of Na and urea of the renal papilla and medulla. The percentile decrease in the concentration of Na and of total solutes in water of the renal papilla was not so great as the fall in maximum urinary osmolality. Renal conservation of Na was impaired. It is concluded that the impairment of renal concentrating ability observed in hypercalcemic rats results at least in part from impaired reabsorption of Na by the renal tubules and a diminished ability to create and maintain a high concentration of Na in the intersti tial fluids of the medulla and papilla. The possibility that the permeability of the collecting ducts to the back-diffusion of water is reduced by vitamin D intoxication is discussed.