Evidence that parathyroid hormone is not required for phosphate homeostasis in renal failure

Varying degrees of renal failure were produced by surgical reduction of renal mass in normal dogs and in thyroparathyroidectomized dogs (TPTX) in whom serum calcium levels were maintained in the normal range by the administration of vitamin D. Both groups of dogs maintained normal serum phosphate levels in spite of progressive decreases in glomerular filtration rates (GFR). Furthermore, both groups of dogs were able to increase the fractional excretion of phosphate as GFR decreased. Thus the same renal response to loss of GFR was maintained in the complete absence of parathyroid tissue. Finally, stable serum phosphate levels and increased fractional excretion of phosphate in response to a decrease in GFR were also demonstrated in acutely TPTX dogs who were not receiving vitamin D. These results indicate that phosphate homeostasis can be maintained in renal failure in the total absence of parathyroid hormone secretion.