NaCl ingestion ameliorates plasma indexes of calcium deficiency

Rats deprived of dietary calcium ingest large volumes of concentrated NaCl solutions. To examine why, some physiological consequences of ingesting NaCl solution were measured. Male Sprague-Dawley rats fed diet containing 150 or 25 mmol Ca2+/kg were killed at 20, 40, 80, or 160 min after they started to drink solutions of 0.125% saccharin+3% glucose (S+G), 50 mM CaCl2, or 300 mM NaCl. Relative to rats fed the 25 mmol Ca2+/kg diet given nothing to drink, those fed the same diet that drank NaCl or CaCl2 but not S+G had elevated plasma ionized calcium concentrations and reduced plasma parathyroid hormone (PTH) concentrations. Rats fed the 150 mmol Ca2+/kg diet did not show these changes. In a follow-up experiment, rats fed the 25 mmol Ca2+/kg diet that drank NaCl had elevated plasma ionized calcium and reduced PTH and 1,25-dihydroxyvitamin D concentrations over the following 4-6 h. An in vitro study found that plasma ionized calcium concentrations were modulated by NaCl concentration directly. These findings indicate that NaCl ingestion can temporarily enhance the calcium status of calcium-deprived rats.