Effect of Sudden Blood Calcium Depletion on Phosphorus Excretion

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Abstract
Ten normal dogs and 10 dogs with total thyroparathyroidectomies had their serum calcium suddenly lowered by 20–30% over an interval of 30 min or less. This was accomplished by direct perfusion of the animal's arterial blood through a 500 g sodium Dowex ion-exchange column. Hourly clearances of calcium, phosphorus and creatinine · were determined on each dog just prior to and for 6½ hr following each perfusion. Three to 5 hr following the perfusion, the 10 normal dogs demonstrated a striking increase in the phosphorus clearance/creatinine clearance ratio. The phosphaturia was completely aborted in the dogs with total thyroparathyroidectomy performed just prior to perfusion with the ion-exchange column. This procedure did not significantly alter the calcium clearance in either group of dogs. These observations suggest that following a sudden reduction in serum calcium there is an outpouring of calcium and phosphorus from bone to restore the serum calcium level. This response is independent of parathyroid activity and may be due to a sudden change in the physicochemical equilibrium between bone calcium and the calcium levels of the extracellular fluid. This is followed in 3–5 hr by a marked phosphaturia in normal dogs with intact parathyroid glands, probably reflecting the effect of increased secretion of parathyroid hormone. (Endocrinology74: 266, 1964)