Metabolism of radium including the transfer to the fetus through the placenta was studied during three successive pregnancies 92, 155, and 213 days after injection of226 Ra in young female rats. The cumulative fecal and urinary excretions of226 Ra in a 213-day period following injection were about 30 and 15% injected dose (%ID), respectively, most of them occurring during the first 42 days. The excretions were similar in both the pregnant and control (unmated) rats. The whole-body burden of radium (mostly in the skeleton) determined by actual analysis of the entire body was similar in the two groups and was about 53, 48, and 44 %ID at the first, second, and third pregnancy, respectively. Pregnancy alone, therefore, did not significantly affect metabolism of radium. At 20 days of gestation the mean placental content of radium was 0.005, 0.0045, and 0.0036 %ID in the first, second, and third litter, respectively; the corresponding mean fetal content was 0.01, 0.008, and 0.005 %ID. The radium burden of the full-term neonate (21-22 days) was 0.014 and 0.011 %ID for the first and second delivery, respectively. The total amount calculated of radium transferred from the mother to the 8-10 fetuses in a litter did not exceed about 0.3% of the maternal content per each pregnancy. Comparison of the ratio of radium and calcium in the fetus and maternal skeleton shows that there is a Ra-Ca discrimination during their passage from the mother to the fetus.

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