We studied six patients with renal stone disease, hypercalciuria, cystinuria and/or hyperuricosuria, during variations in dietary Na and Cl intake. Switching between equimolar NaCl and NaHCO3intakes reduced urinary Ca (UCa) during the NaHCO3phase, despite steady-state urinary Na. Switching between equimolar NaCl and KCl did not change UCa, despite a sharp fall in UNa. The results suggest a predominant role for Cl rather than Na ions during sodium-chloride-induced changes in UCa. In stone disease of mixed aetiology, where alkalinization of the urine as well as reduction in UCa may be desirable, treatment with NaHCO3loading is not accompanied by a rise in UCa, provided that dietary Cl is maintained moderately low at 80–100 mmol/day. The mechanism whereby Cl intake influences UCa remains undefined. Plasma PTH and calcitriol levels showed no significant alteration, and atrial natriuretic peptide levels in one patient remained unchange
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