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

Abstract

Rats on a low phosphorus diet excreted less urinary phosphorus than control rats, although the serum phosphorus level was elevated more than the normal level after intravenous injection of inorganic phosphate. Repeated intravenous injections of the phosphate, however, resulted in hyperphosphaturia, although serum phosphorus remained at the same or a lower level than before the injection. Furthermore, it was often observed that there was a lag of 30 minutes or more before starting a continuous phosphaturia induced by the acute injection of the phosphate. In the rats on a low phosphorus diet, serum calcium concentration was found to be elevated above normal but parathyroidectomy caused neither hypocalcemia nor hyperphosphatemia. The effects of parathyroidectomy which had been masked by the low phosphorus intake became apparent shortly after the injection of the inorganic phosphate. The injection caused less phosphaturia and more hyperphosphatemia than in the control rats, resulting in a decrease in serum calcium only in the former but not in the latter. 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.