Impact of stress and triiodothyronine on plasma magnesium fractions.

The differential regulation of free and bound plasma magnesium was studied in healthy volunteers exposed to various forms of stress, and patients screened for thyroid disorder. Both ergometric (7 min) and psychological (45 min) stress had no effect on free plasma magnesium, but increased the bound fraction. Before combined physical and psychological stress (45 min aerobatics) there was no correlation between the plasma fractions of magnesium; thereafter, there was a strong negative correlation between increased free and decreased bound magnesium. Three days of training in ground combat increased significantly the plasma levels of both magnesium fractions. Patients screened for thyroid disorder had a significant, positive correlation between both plasma fractions of magnesium, and a highly significant negative correlation between plasma T3 and the two magnesium fractions. No clear correlation between plasma catecholamines and magnesium levels was seen under any of the above conditions. Overall, the data show that the evaluation of the functions of circulating magnesium requires the specific measurement of the free and bound fractions.