1. Sodium phosphate was infused intravenously over approximately 2½ h and produced a mean linear rise in plasma phosphorus levels of 9·1 mg/100 ml. Twenty-one infusions were performed in twelve control subjects and thirty-eight were carried out in thirty-two patients with disorders of calcium and phosphorus metabolism.

2. The fall in plasma calcium under these conditions was related to:

  • a.

    The initial height of plasma calcium.

  • b.

    The rate of rise of plasma phosphorus.

  • c.

    The initial level of plasma phosphorus and the theoretical renal phosphorus threshold.

  • d.

    The presence of metabolic bone disease.

The fall in plasma calcium levels per mg rise in plasma phosphorus was greater in patients with hyperparathyroidism, osteomalacia, osteoporosis, Paget's disease and certain other rarer conditions than in the control group or in patients with hypoparathyroidism, whose plasma calcium levels changed least of all.

3. It was concluded that pre-existing increased bone resorption or osteoblastic activity may determine the degree of hypocalcaemia which occurs under these conditions.

4. Phosphate was also infused at a constant rate over 10 h in five tests on five patients with moderately severe hypercalcaemia (plasma calcium 14·0–17·3 mg/100 ml). Plasma calcium levels fell steadily, and small or negligible changes were seen in serial determinations of glomerular filtration, urine protein and cell excretion rate.

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