Neutral phosphate administration generates and maintains renal metabolic alkalosis and hyperparathyroidism

We examined the effects of chronic intravenous neutral phosphate administration on systemic acid-base equilibrium and parathyroid function in six normal, NaCl-replete male human subjects under metabolic balance conditions. The subjects received 4.35 mmol of neutral sodium phosphate.kg body wt-1.day-1 intravenously and continuously for 7 days and the same amount of sodium as NaCl during control and recovery. Blood pH increased from 7.388 to 7.411 (P < 0.001) and plasma bicarbonate from 23.5 to 26.0 mmol/l (P < 0.001). Urinary pH increased from 6.58 to 6.79 (P < 0.001). Net acid excretion increased from 59 to 100 mmol/24 h (P < 0.001). Plasma ionized calcium concentration decreased and plasma phosphate concentration increased transiently. Serum intact parathyroid hormone increased from 24 to 62 pg/ml (P < 0.001). Chronic phosphate administration also resulted in a significant increase in renal phosphate clearance (35 to 229 ml/min) and decrease in the fractional excretion of calcium (1.8 to 0.9%). Thus chronic intravenous phosphate administration generates and maintains renal metabolic alkalosis in salt-replete humans and induces hyperparathyroidism. The severity of metabolic alkalosis is mitigated by an apparent increase in effective endogenous acid production as evidenced by the significant increase in steady-state net acid excretion.