Abstract
Summary
Mature and immature rats were injected with radioacitve magnesium and distribution of the isotope in various tissues was measured. The exchange with plasma magnesium was rapid and complete within 3 hours in liver, kidney, and heart muscle. In brain, testes, erythrocytes and skeletal muscle there was a rapidly exchanging component similar to that in liver, etc., but more than half the magnesium exchanged very slowly. The similarity between functionally disparate tissues in each of the 2 groups suggests that the magnesium is present in 2 or more physiologic states. In one state the turnover time is 1.2 hours and in the other it is 25 hours. The exchange was faster in muscles which were stimulated to contract repeatedly than in resting muscles. In immature rats uptake of radioactive magnesium by the testes was slightly faster than in the mature animals and net decay of plasma activity was faster but there were no other significant differences.
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