Magnesium appetite in the rat

Rats modify their ingestive behaviour to correct deficiencies of minerals such as sodium and calcium. Here, we examined the effect of magnesium deprivation on the ingestion of MgCl2 and other solutions. Male Sprague-Dawley rats were fed a nutritionally complete or magnesium-deficient diet and were then given 3·2, 10, 32, or 100 mM MgCl2, 32 mM CaCl2, 32 mM NaCl, 10 mM HCl, or 2·5 mM saccharin, and their intake was measured for 24 h in a two-bottle choice test with water. Within the first 5 min, magnesium-deprived subjects given 3·2, 32, or 100 mM MgCl2 or 32 mM CaCl2 drank significantly more of these solutions than did replete rats. In a separate study, rats fed replete, magnesium-deficient, or calcium-deficient diets were given a three-bottle choice between water, 32 mM MgCl2, and 32 mM CaCl2. The deprived rats preferred the solution that ameliorated their deficiency; for example, during the first 1 h, the magnesium-deprived rats drank 3·1±0·5 ml MgCl2 and 1·1±0·4 ml CaCl2, whereas the calcium-deprived rats drank 1·8±0·5 ml MgCl2 and 3·9±0·4 ml CaCl2. Thus, magnesium deprivation leads to a compensatory appetite for magnesium, and the appetites for magnesium and calcium are distinct and specific. The rapid expression of magnesium appetite suggests that it depends in part on innate, gustatory factors.