Influence of dietary phosphorus on renal phosphate reabsorption in the parathyroidectomized rat

was studied during Pi infusion, after acute or chronic thyroparathyroidectomy (TPTX), in rats stabilized on a high-phosphorus (1%0 P) or a low-phosphorus (0.02%0 P) diet. After acute TPTX, there were no consistent differences in Pi reabsorption between the high- and low-phosphorus dietary groups. After chronic TPTX, the rats stabilized on the low-phosphorus diet exhibited nearly complete Pi reabsorption at every plasma Pi level, while the animals receiving the high-phosphorus diet manifested a marked phosphaturic response to Pi infusion. In addition, Pi reabsorption was significantly increased in the chronic TPTX low-phosphorus rats which achieved the highest filtered Pi loads, while their urine remained essentially phosphate-free. Dietary phosphorus-dependent alterations in Pi reabsorption may play a significant role in establishing the rate of Pi excretion per nephron under certain circumstances and should be considered in the inter-pretation of studies investigating renal Pi handling. The ability of phosphorus-depleted animals to main-tain a phosphate-free urine during Pi loading would favor the rapid repletion of body phosphorus stores