The Requirement and Tissue Distribution of Magnesium in the Rat as Influenced by Environmental Temperature and Dietary Calcium

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Abstract
Five hundred twenty-two rats were used in a single investigation of the effect of environmental temperature (10 and 23°C), duration of experiment, (one to 4 weeks) and dietary calcium level (0.2, 0.4, and 0.8%) on the requirement of the rat for magnesium. For maximum weight gain the average requirement was 115 ppm, a value not affected by environmental temperature or time on experiment, but averaging 100, 116 and 130 ppm at increasing calcium levels. For maintenance of “normal” blood magnesium levels an average of 365 ppm was required. This value was unaffected by time or temperature, but was influenced by dietary clcium, being 285, 399 and 413 ppm at increasing calcium levels. For maintenance of “normal” bone magnesium levels an average of 288 ppm was required. This value varied with temperature, being 221 ppm at 10°C and 354 ppm at 23°C, with calcium level, being 264, 281 and 318 ppm at increasing calcium concentrations, and with time, being 207, 258, 320 and 325 ppm at successive weekly intervals. It was noted that when supplied the basal diet (20 ppm of magnesium), rats could lose 80% of the magnesium originally present in their femurs while still gaining in femur calcium. Calcification of kidneys of rats on magnesium-deficient diets was marked as early as 7 days on experiment and amounted to as much as an 11-fold increase in calcium concentration, while kidney magnesium was unchanged.