MECHANISM OF INORGANIC PHOSPHATE DIURESIS SECONDARY TO SALINE INFUSIONS IN RAT - EXCRETION OF SODIUM, INORGANIC PHOSPHATE, AND CALCIUM IN NORMAL AND IN PARATHYROIDECTOMIZED RATS

Clearance studies have been performed in rats undergoing saline diuresis. Saline infusion was increased from 0.15 to 0.5 ml/min during each experiment in order to examine the effect of extracellular fluid volume expansion on the excretion of sodium, inorganic phosphate, and calcium in normal and parathyroidectomized animals. In normal animals excretion of sodium, inorganic phosphate, and calcium increased significantly (P<0.001) from 13.7 to 56.6 μEq/min, from 0.69 to 1.34 μM/min, and from 0.54 to 0.87 μEq/min, respectively, under these conditions. Fractional excretion of sodium rose from 3.8 to 13.3%, fractional excretion of inorganic phosphate from 13.8 to 27.2%, when infusion rate was elevated from 0.15 to 0.5 ml/min. In parathyroidectomized animals excretion rates of sodium and calcium were similar. In contrast, after parathyroidectomy inorganic phosphate excretion was almost abolished, being 0.0058 and 0.0121 μM/min or 0.2 and 0.3% of filtered inorganic phosphate at the lower and the higher infusion rate, respectively. It is concluded, that the presence of intact parathyroids is a prerequisite for the mediation of the normal phosphaturic response secondary to saline infusions. © 1969 Springer-Verlag.