Voluntary intake of calcium and other minerals by rats

The voluntary intake by male Sprague-Dawley rats of five calcium salts and eight mineral chlorides was assessed. Groups of 12-25 rats received a series of 48-h two-bottle tests with a choice between water and ascending concentrations of a mineral solution. Similar inverted U-shaped concentration-intake functions were obtained with each of the five calcium salts tested (hydroxide, gluconate, phosphate, lactate, and chloride): rats drank more calcium solution than water at concentrations between approximately 0.2 and 5 mM, showed indifference between 5 and 12 mM, and avoided higher concentrations. Inverted U-shaped concentration-intake functions were also obtained for ammonium chloride (peak at 100 mM), magnesium chloride (peak at 10 microM), potassium chloride (peak at 10 mM), ferrous chloride (peak at 4.64 microM), and rubidium chloride (peak at 2.15 mM). Rats drank slightly and nonsignificantly more 2.15 microM aluminum chloride than water and never drank more zinc chloride than water (range tested, 1 microM to 464 mM). These results illustrate that, as is the case for sodium, rats spontaneously ingest low concentrations of calcium and several other mineral solutions in preference to water. In general, the lower the cation's ionic charge, the greater the intake and higher the most accepted concentration.