The influence of different dietary magnesium levels on the metabolism of calcium, phosphorus and magnesium in growing rats

Material and methods: 30 male Sprague Dawley rats were divided into three groups each of ten and housed in non-metal metabolic cages individually. The rats in the first group were fed Mg-deficient diet (86 mg/kg), the rats in the second group were fed Mg-adequate diet (548 mg/kg) while in the third group fed Mg-excess diet (5402 mg/kg). All the diets were semisynthetic containing Ca: 3.7 g/kg. P: 4 g/kg. After 25 days feeding acid adaptation to the metabolic cages, the five-day period of metabolic experiment was carried on. The samples of feces and urine were collected, respectively. At the end of the period. heparinized fasting blood samples were taken from the heart under light anesthesia The femur and tibia were dissected, after having measured weight, length and volume, stored together with kidney at -20 degrees C until analysis for Ca, Mg and P. Results: There was no much influence on the apparent absorption of Ca (86%) at the Mg-deficient or -adequate Mg supplement, excess Mg in diet made this absorption of Ca decrease a little (83%). However, excess Mg increased urinary Ca excretion significantly decreased the retention of Ca. Magnesium-deficient diet increased the P excretion in urine obviously and reduced the retention of P in the body. With the increase of Mg contents in diet, the Mg excretion in feces and urine increased significantly, that means the homeostasis of ME is regulated by both intestine and kidney. Conclusion: With respect to the growing rats, both Mg deficiency and excess in diet are detrimental to the skeletal growth and development. Mg-deficient diet caused calcium accumulation in kidney, probably involving in the pathogenesis of nephrolithiasis.