Effect of hypomagnesemia and exercise on slowly exchanging pools of magnesium

The effects of hypomagnesemia and exercise on the slowly exchanging pools of magnesium, skeletal muscle, bone, erythrocytes, and plasma, were examined in four groups of male Sprague-Dawley rats: sedentary-normal diet (SN), exercise-normal diet (EN), sedentary-hypomagnesemic diet (SH), and exercise-hypomagnesemic diet (EH). The exercise groups swam 5 d/wk-1 for 6 weeks. The hypomagnesemic diet contained 80 ppm and the normal diet about 640 ppm of magnesium. Compared with normal-diet rats (SN and EN), dietary-deficient rats (SH and EH) gained less weight and had lower concentrations of magnesium in all tissue samples and plasma (P less than .01). Exercise groups (EN and EH) demonstrated significantly higher magnesium levels in skeletal muscle (P less than .01) and a tendency for lower levels of magnesium in plasma, erythrocytes, and bone compared with sedentary groups (SN & SH). EH rats normalized skeletal muscle magnesium, mEq.kg-1 wet tissue, (19.9 +/- 5.1) compared with the SN group (20.6 +/- 2.1). Assuming that magnesium stores that are rapidly exchanged are maintained at the expense of those that are slowly exchanged, magnesium stores in skeletal muscle appear to be most protected, with the effect accentuated by exercise.