Progressive Changes in Renal Phosphate and Calcium Excretion in Rats Following Parathyroidectomy or Parathyroid Administration. ∗

Abstract

Summary

This study has dealt with progressive changes which occur in renal phosphate and calcium excretion rates in rats during the first 27 hours after parathyroidectomy or the first injection of parathyroid extract. Following parathyroidectomy there is an immediate drop in urinary phosphate and a rise in urinary calcium. Within 24 hours the excretory rates for both these ions return to normal despite the continued high phosphate and low calcium levels of the serum. Following the initiation of parathyroid extract administration to normal rats the reverse is true. There is an immediate drop in urinary calcium and a rise in urinary phosphate. Twenty-four hours later the excretory rate for calcium returns to or rises above normal. The urinary phosphate, however, continues high throughout the entire period. These data are explained on the basis that immediate changes in renal excretory rates resulting from changes in parathyroid hormone titer are due to shifts in the renal threshold for these two ions. Excretion changes seen after the serum level has become adjusted to the new thresholds are considered to be due to extra-renal changes increasing or decreasing the entry of these ions into the serum.