Magnesium appetite in the rat

Abstract

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 100mM MgCl2, 32mM CaCl2, 32mM NaCl, 10mM HCl, or 2.5mM saccharin, and their intake was measured for 24h in a two-bottle choice test with water. Within the first 5 min, magnesium-deprived subjects given 3.2, 32, or 100mM MgCl2 or 32mM 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, 32mM MgCl2, and 32mM CaCl2. The deprived rats preferred the solution that ameliorated their deficiency; for example, during the first 1h, the magnesium-deprived rats drank 3.1 +/- 0.5ml MgCl2 and 1.1 +/- 0.4ml CaCl2, whereas the calcium-deprived rats drank 1.8 +/- 0.5ml MgCl2 and 3.9 +/- 0.4ml 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.