Effects of phosphate loading and depletion on the renal excretion and reabsorption of inorganic phosphate.

A number of studies have indicated that parathyroid 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 extracellular concentration and/or the dietary intake of calcium and phosphate. Although dietary variations of these ions did not correlate consistently with TmP 8 in our initial investigations (7), other workers have demonstrated an influence of diet on phosphate reabsorption. 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 influenced 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 phosphate solutions were administered intravenously daily for four to eight days to the normal and hypoparathyroid subjects previously described (7). Another phase of this study involved an inquiry into the mechanism by which aluminum gels produce a marked reduction in urinary P. Variations in plasma levels of Ca and P often occur together. An attempt was made to separate the effects of elevation of plasma P from the frequently seen simultaneous reduction in plasma Ca. Our data indicate that repeated daily intravenous administration of large quantities of phos-