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Abstract: FR-PO310

Magnesium Decreases Urine Supersaturation but Not Calcium Oxalate Stone Formation in Genetic Hypercalciuric Stone-Forming Rats

Session Information

Category: Bone and Mineral Metabolism

  • 501 Bone and Mineral Metabolism: Basic

Authors

  • Li, Qiaoli, Thomas Jefferson University, Philadelphia, Pennsylvania, United States
  • Krieger, Nancy S., University of Rochester, Rochester, New York, United States
  • Yang, Lee, Laboratory Corporation of America Holdings, Itasca, Illinois, United States
  • Asplin, John R., Laboratory Corporation of America Holdings, Itasca, Illinois, United States
  • Bushinsky, David A., University of Rochester, Rochester, New York, United States
Background

This study assessed the effect of oral magnesium on urine parameters and stone formation in a genetic hypercalciuric stone-forming (GHS) rat model of human idiopathic hypercalciuria.

Methods

When fed the oxalate precursor, hydroxyproline, every GHS rat develops calcium oxalate stones. These rats, fed a normal calcium (Ca) and phosphorus (P) diet with hydroxyproline, were divided into three groups of ten rats per group: control diet with 4.0 g/kg MgO, low MgO diet (0.5 g/kg), and high MgO diet (8.0 g/kg). At baseline and at 6 weeks, twenty-four-hour urines were collected, and urine chemistry and supersaturation were determined. Stone formation was quantified.

Results

After six weeks those fed the low Mg diet had a significant reduction in urinary Mg and those fed the high Mg diet had a significant increase in urinary Mg compared to those fed the control diet. Dietary Mg did not alter urine Ca excretion while the low Mg diet led to a significant fall in urinary Ox. The low Mg diet increased urinary NH4 and decreased urinary citrate while the high Mg diet reduced urinary NH4 and increased urinary citrate. Urine supersaturation with respect to calcium oxalate was significantly increased with low Mg, whereas urine supersaturation was significantly decreased with high Mg. Neither a low nor high Mg diet altered kidney stone formation.

Conclusion

In genetic hypercalciuric stone-forming rats, dietary Mg significantly altered urinary CaOx supersaturation; a low Mg diet increased and a high Mg diet decreased CaOx supersaturation. There was no effect of dietary Mg on stone formation within 6 weeks of treatment.

Urine supersaturation (SS) of CaOx was differentially regulated by Mg. Results are mean ± SEM. *P < 0.05 versus CTL; oP < 0.05 versus low Mg.

Funding

  • NIDDK Support