Age, diet, and temperature effects on magnesium behavior in rats

Recent recognition of hypomagnesemia and a condition in ruminant animals called "grass tetany" has augmented investigations of factors affecting the behavior or metabolism of magnesium. In the present study an attempt was made to interrelate body magnesium with ambient temperatures, age and selected dietary factors, using 96 young and old male rats. Results indicated that rats maintained at 3°C consumed more feed than those maintained at 23°C. Serum Protein bound iodine (PBI) values in rats receiving low iodine diet decreased in cold, and both serum magnesium and PBI levels decreased in rats on the high potassium diet, irrespective of temperature. Tissue magnesium and calcium concentration increased on addition of dietary iodine, suggesting a greater utilization of these minerals in the presence of iodine. Kidney was the principal excretory route for both magnesium and 28 magnesium. On the normal magnesium ration, addition of iodine increased excretion of magnesium and 28 magnesium in cold exposed rats. High dietary potassium also decreased absorption, retention and tissue magnesium concentration, especially in young rats. Turnover rate of radiomagnesium was higher in soft tissues and lower in bone. Concentrations of other minerals further reflected metabolic effects.