The impact of diets with different magnesium contents on magnesium and calcium in serum and tissues of the rat

The impact of three different magnesium diets (70, 1000 and 9000 ppm) on to tal, ionized and bound magnesium as well as ionized calcium in serum and to tal calcium and magnesium in femoral bone, skeletal muscle, heart and liver of male Sprague-Dawley rats was investigated. The percentage of ionized se rum magnesium was unproportionally high in rats fed a low magnesium (70 ppm ) diet. Femoral magnesium was correlated with ionized and total serum magne sium. In contrast, there was generally no con elation between total serum m agnesium and the magnesium fractions in skeletal muscle, heart and liver. I n rats fed the magnesium deficient diet, total cardiac concentration of mag nesium was even significantly increased along with total calcium content, w hile there were no effects on total muscle and liver magnesium. Within the single groups, ionized serum calcium was never proportional to dietary magn esium, but in all three magnesium diet groups together, it was inversely co rrelated with dietary magnesium. Moreover, ionized serum calcium was invers ely correlated with both ionized and total serum magnesium. In all 3 groups together, the concentrations of total calcium and magnesium in heart and s keletal muscle were correlated, within the single groups correlation existe d only in the 1000 ppm group. Magnesium influx via calcium channels during low magnesium intake has been seen in non cardiac tissues [35,36], but noth ing similar is known about non selective channels for divalent cations in t he heart [33]. Thus, magnesium uptake by cardiac cells along with calcium s eems to be possible, especially at low intracellular magnesium concentratio ns, but is still poorly investigated. We suggest that the calcium-antagonis tic effect of magnesium is related to the turnover rate of magnesium rather than to its tissue concentrations. (C) 2000 Elsevier Science Inc. All righ ts reserved.