Parathyroid Influences upon Phosphorus Balance and Homeostasis in Cows

Abstract

Phosphorus balance studies were conducted on 4 cows during periods of experimentally altered parathyroid status. Parathyroid extract administration to intact and parathyroidectomized cows was accompanied by an increase of urinary phosphorus and a decrease in fecal phosphorus. Parathyroidectomy was followed by a decline in urinary phosphorus output and a rise in fecal phosphorus. The reciprocal changes between urinary and fecal phosphorus excretion during periods of altered parathyroid status resulted in minimal changes in plasma inorganic phosphorus concentration and phosphorus balance. Phosphorus homeostasis during parathyroid extract administration appeared to be preserved principally through a reduction of fecal phosphorus output rather than by liberation of phosphorus from bone. Although the changes in fecal phosphorus excretion are compatible with a parathyroid hormone-induced enhancement of phosphorus absorption, the data do not permit a definitive conclusion regarding such an effect.