Research Article| Volume 63, ISSUE 1, P80-99, January 1964

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Metabolism of magnesium in the normal rat

  • Jerry G. Chutkow
    From the Argonne Cancer Research Hospital (operated by the University of Chicago for the United States Atomic Energy Commission) Chicago, Ill. U.S.A.

    From the Department of Medicine, University of Chicago Chicago, Ill. U.S.A.
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      Several aspects of magnesium metabolism in the rat were investigated using Mg28 and very low background level gamma-ray spectrometry. By 120 hours after parenteral injection, young animals (mean weight, 110 grams) excreted an average of 65.8 per cent of the Mg28 in the urine and 12.3 per cent in the feces. Approximately 20 per cent of the daily endogenous magnesium loss occurred via the stool. Two “compartments” with half-lives of 11.5 and 93.0 hours accounted for 36.0 and 51.5 per cent of the isotope, respectively. Within 3 minutes, intravenously administered Mg28 had penetrated a volume exceeding the estimated extracellular space. After an initial rapid fall, the plasma radioactivity declined exponentially, with a Math Eq of 27.5 hours. Absorption of the isotope averaged 53.5 per cent. Acute hypermagnesemia induced by intraperitoneal administration of magnesium quantitatively increased the excretion of carrier in the urine much more than in the feces and had no effect on absorption. While no upper limit to absorption short of diarrhea was found, large amounts of orally administered magnesium did depress the subsequent absorption of Mg28 for at least 7 to 8 hours. Qualitatively, little change in the absorption, excretion, and retention of magnesium was demonstrated with aging. Under the experimental conditions described in these studies, it is concluded that in the rat the major regulator of absorption is the quantity of magnesium in the intestinal lumen rather than the nutritional requirements of the animal; the feces constitute a significant route of endogenous magnesium loss with little obvious adaptive value to an animal faced with detrimental alterations in magnesium balance, and acute endogenous magnesium excesses are handled for all practical purposes by rapid renal excretion and net tissue uptake.
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