Dependence of Fetal Growth and Storage of Calcium and Phosphorus on the Parathyroid Function and Diet of Pregnant Rats

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Abstract
In rats with intact parathyroids fetal growth and storage of calcium and phosphorus may show little difference in spite of large differences in the maternal intake of these elements. A diet nearly devoid of calcium does not necessarily prevent normal fetal growth or alter the mineral composition of the offspring. However, if the maternal diet contains an overabundance of calcium, so that the Ca/P ratio is abnormally high (diet no. 16 of Cox and Imboden, Ca 1.225%, P 0.245%, Ca/P ratio = 5), the deposition of bone salts in the embryo is definitely impaired. Normal development of the fetus, including growth and calcification, depends on the parathyroid function of the maternal organism. Lack of parathyroid secretion during pregnancy disturbs the mineral metabolism, not only on the maternal side, but also on the fetal side of the placental barrier. The dominance of maternal parathyroid function as a factor in fetal development was abolished in rats fed rachitogenic diet no. 16 of Cox and Imboden. On this diet, parathyroidectomized and normal rats produced young which did not differ significantly in composition. On a given diet, differences in the fetal storage of calcium and phosphorus between normal and parathyroidectomized rats were not due to differences in the amounts of food consumed during the period of gestation. Administration of viosterol to parathyroidectomized rats fed certain diets produced a moderate increase in the average concentration of serum calcium and definite improvement in average fetal growth and fetal storage of calcium and phosphorus. An even more conspicuous effect was obtained by incorporating 4% of aluminum acetate in the diet of the pregnant parathyroidectomized rats. Associated with the reduction of the serum inorganic phosphorus and increase in the serum calcium there was marked improvement in fetal growth and in fetal storage of calcium and phosphorus. It is concluded that the development of the fetus and its ability to store calcium and phosphorus depend on the maintenance of suitable concentrations of calcium and phosphorus in the blood on the maternal side, and, presumably, also on the fetal side, of the placental barrier.