Effect of Phosphate Depletion on Magnesium Homeostasis in Rats

Abstract

A B S T R A C T The effects of phosphate depletion on magniesiumni (NMg) homeostasis were evaluated in rats fed a diet containing 0.03% phosphorus for periods up to 8 wk. Plasma phosphorus fell signiificantly (P < 0.01) from 10.1+0.27 (SE) to 5.0±0.54 mgIl00 ml within 1 day and conitiniued to fall gradually to a level of 1.2±0.21 mg/100 ml by the end of the 8th wk. A signiificant (P < 0.01) increment in urinary Mg excretion (UMgV) from 46±2.7 to 126±24 ,ueq/24 h occurred during the 1st day of phosphate depletion; UMgV reached a peak of 300±+24 pieq/24 h by the 3rd day and remained high ranging between 150-300 ,ueq/24 h, thereafter. The magnittude of the magnesuria was related to the degree of hypophosphatemia and was not affected by lowering the calcium intake and reducing the hypercalciuria. The concentration of plasma Mg fell significantly (P < 0.01) from 1.2±0.02 to 0.79±0.10 meq/liter by the 1st day of the study and remained low throughout.Mg balance became negative during the 1st day of phosphate depletion and remained so during the entire study. This occurred despite a significant increment in the fraction of ingested Mg absorbed which becarmie evident by the 3rd wk of phosphate depletion. Mg contenit of muscle, kidney, and liver were not affected but bone Mg was reduced significantly. The change in bone Mg was not due to an overall reduction in bone mineral contenit because bone calcium content was not affected. Supplementation of large amounts of Mg (800-1,000 ,ueq/day) in the drinking water produced a normalization of serum Mg but did not bring about restoration of bone Mg despite a positive Mg balance. The disturbances in Mg metabolism were independent of the age or veight of the animals.Our results indicate that phosphate depletion is Dr. Kreusser is a Fellow of the Deutsche Forschungsgemeinschaft.Dr. Aznar is a Fellow of the Del Amo Foundation.

Healing of rickets with phosphate supplementation in the hypophosphatemic male mouse.

“…The increased Mg excretion associated in untreated Hyp/Y with a slight hypermagnesemia appears to result from the deranged Pi homeostasis since correction of serum and urinary Mg concentrations could be achieved by Pi supplementation. In the rat, Pi depletion increases the Mg intestinal absorption and decreases the net renal tubular reabsorption of Mg with the main source of urinary loss being bone (11). In Hyp/Y mice, it is possible that correction ofbone Mg content will require the normalization of endosteal bone mineralization.…”

Epithelial magnesium transport and regulation by the kidney

“…Magnesium excretion may be sufficiently large to lead to hypomagnesemia (154,155). The increase in divalent ion excretion in both human and animals occurs within hours following initiation of dietary phosphate restriction.…”

Renal Magnesium and Phosphate Wastage in a Patient with Hypercalciuria and Nephrocalcinosis: Effect of Oral Phosphorus and Magnesium Supplements

“…This is however unlikely in our patient since magnesium supplements apparently did not correct the phosphate leak. Conversely, several data indicate [15][16][17] that phosphate depletion results in elevated urinary mag nesium excretion with a modest decrease in plasma mag nesium concentration. The decrease in mean TRP, 65.7 ± 4.4% (SD) vs. 54.4 ± 6.5%, respectively, prior to and during phosphorus supplementation indicates that phos phorus supplements were at least partially absorbed.…”