CHANGES IN TISSUE CALCIUM AND PHOSPHORUS-CONTENT AND PLASMA-CONCENTRATIONS OF PARATHYROID-HORMONE AND CALCITONIN AFTER LONG-TERM MAGNESIUM-DEFICIENCY IN RATS

Objective: The present study was undertaken to investigate the effect of dietary magnesium (Mg) deficiency on plasma levels of parathyroid h ormone (PTH) and calcitonin (CT), and the changes in tissue calcium (C a) and phosphorus (P) content. Methods: Wistar rats were fed an Mg-def icient diet. Plasma levels of PTH and CT, and Ca and P content in plas ma, whole blood, skeletal muscle, heart, kidney, femoral bone and brai n, were determined after 7, 35, 42, 49, 56, 63 and 70 days. Results: M g deficiency significantly increased plasma levels of ionic Ca after 1 week of deficiency, and significantly increased total Ca in plasma an d whole blood after 5 weeks. Whole blood and plasma levels of P decrea sed significantly after 8 and 5 weeks, respectively, in comparison wit h values obtained in pair-fed control rats. Plasma levels of CT were n ot modified by hypercalcemia and hypomagnesemia. Plasma PTH decreased significantly during the first 3 weeks, then recovered gradually, reac hing control values in week 7 and remaining stable thereafter, despite elevated levels of ionic Ca. The Mg-deficient diet led to calcificati on in skeletal muscle, heart, kidney and femur, detectable as early as week 5. However, P content increased only in kidney after 1 week, dec reased in heart and femur after 5 weeks, and did not change in muscle. The Mg-deficient diet did not significantly modify Ca or P content in brain. Conclusion: Mg deficiency led to tissue calcification and decr eased P levels in blood, heart, and femur. These changes did not affec t CT secretion. PTH appeared to be more closely related with hypomagne semia than with hypercalcemia.