Effects of Phosphate Loading and Depletion on the Renal Excretion and Reabsorption of Inorganic Phosphate

A number of studies have indicated that para- thyroid extract increases the renal excretion of phosphate (1-6). This effect appears to result from a depression of the renal reabsorption of phosphate (6). Endogenous secretory activity of the parathyroid glands has been related to the ex- tracellular concentration and/or the dietary intake of calcium and phosphate. Although dietary vari- ations of these ions did not correlate consistently with TmP 8 in our initial investigations ( A high phosphate diet led to a diminished P reabsorption in normal but not in parathyroidectomized rats (8). Studies in dogs (9) and in normal human subjects (8, 10) also indicated that the level of P intake in- fluenced P reabsorption, but whether this effect was mediated by the parathyroid glands is not clear. In order to examine more rigorously the effects of a high P intake, buffered sodium phos- phate solutions were administered intravenously daily for four to eight days to the normal and hy- poparathyroid subjects previously described (7). Another phase of this study involved an inquiry into the mechanism by which aluminum gels pro- duce a marked reduction in urinary P.