Sodium, potassium, magnesium and calcium tissue levels in the rat during pregnancy.

The concentration of sodium, potassium, magnesium and calcium in the tissue of 12-, 19- and 21-day pregnant rats as well as in controls and in their fetuses have been measured. Practically no changes in sodium, potassium or magnesium concentrations were detected in either maternal or fetal tissues. However, an important calcium accretion in fetuses was observed in the last quarter of intrauterine development, which paralleled a noticeable decrease in calcium stores of bone and kidney, which was followed by muscle calcium loss on day 21. This huge mobilization of calcium and stability of the other metals studied have been discussed in the light of available information as to their availability in the diet and their handling by rat placenta.