ADAPTATION IN RENAL PHOSPHORUS EXCRETION UNDER THE INFLUENCE OF PARATHYROIDS; A STUDY IN URETERALLY CATHETERIZED RATS

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1 The rats placed on low phosphorus diet excreted less phosphorus in the urine than control rats, though serum phosphorus level in the phosphrus-deficient rats was elevated higher than the normal level by an intravenous injection of inorganic phosphate.
2 Repeated intravenous injections of inorganic phosphate into phosphorusdeficient rats resulted in hyperphosphaturia, though serum phosphorus remained at the same or rather lower level than before the injection.
3 It was often observed that there was a lag of 30 mins.or more before starting a continuous phosphaturia induced by an acute intravenous injection of inorganic phosphate.
4 Low phosphorus intake caused a significant increase in serum calcium concentration.
5 Parathyroidectomy caused no hypocalcemia nor hyperphosphatemia in the rats fed on low phosphorus diet.
6 Effects of parathyroidectomy which had been masked by low phosphorus intake became apparent shortly after the injection of the phosphate.The injection caused less phosphaturia and more hyperphosphatemia in the parathyroidectomized rats than in the control rats, resulting in a decrease in serum calcium only in the formers but not in the latters.
7 These results seem to suggest that there is an adaptive change in the renal threshold for phosphorus excretion in response to excess or low phosphorus intake, and that the parathyroids are involved in the mechanism of the adaptation.