Calcium deprivation increases salt intake.

Relative to rats fed chow or semisynthetic control diet, rats fed Ca2(+)-deficient diet increased daily "spontaneous" intake of 0.3 M NaCl solution by as much as eightfold. Intake of 0.3 M NaCl increased in monotonic relationship to the severity of Ca2+ deficiency, which was manipulated by both duration of depletion (0-32 days) and dietary Ca2+ content (0-50 mmol/kg Ca2+). The increased intake was specific to either Na+ or saltiness; relative to controls, Ca2(+)-deprived rats drank more of a wide range of NaCl solutions (0.05-0.50 M) but the same volume of 0.37 mM sucrose octaacetate (bitter), slightly more 2.5 mM citrate (sour), and significantly less 2.5 mM saccharin (sweet). Although urine volume of Ca2(+)-deprived rats was increased, total Na+ excretion was slightly decreased. Adrenal weights, hematocrit, and plasma concentrations of Na+, aldosterone, and angiotensin I were all normal. These results reveal that Ca2+ deficiency increases NaCl intake and thus challenge the notion that salt appetite is a specific response to perturbed Na+ homeostasis.