Nephrocalcinosis without functional renal impairment in rats subjected to subacute moderate magnesium deficiency, and intervention studies on the mobilization of calcium deposits.

Female Sprague-Dawley rats (100-120 g) were kept for 12 d on diets containing 250, 1500, or 9000 ppm Mg. Then subgroups were loaded with water, frusemide or magnesium and urine was collected over 6 h. Moderately Mg-deficient diet (250 ppm) induced moderate hypomagnesaemia (62.3% of controls), but did not result in hypercalcaemia or the formation of typical erythema. Nevertheless, pronounced nephrocalcinosis developed, as shown by increased renal wet and dry weight and elevated tissue concentrations of Ca, P and Mg, the calculous deposits probably consisting to a large extent of Ca3 (PO4)2. Despite these alterations, renal function remained unimpaired in Mg-deficient rats, as shown by normal urinary creatinine excretion and the unaffected ability of the kidneys to concentrate urine. Loading with water, frusemide or Mg increased urinary excretion of calcium in all three diet groups to a similar extent; hence no significant proof can be given that calculous deposits are mobilized under these conditions. Since comparable conditions may also be present under clinical conditions in man, special care should be given to maintain optimal Mg balance.