STUDIES ON THE PASSAGE OF RADIO-ACTIVE THYROXINE AND IODIDE THROUGH RABBIT PLACENTA, ILLUSTRATED BY PAPER CHROMATOGRAPHY

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Abstract
The butanol extract from maternal and fetal serum showed in 5 subjects that no radioactive thyroxine could be demonstrated by paper chromatography in the fetal serum 1/2-1 1/2 hours after injection. No clear explanation is evident. It may be that thyroxine cannot pass the placental barrier, or it may pass through but be used up so quickly that it cannot be demonstrated. Or, it may be disintegrated in the placenta. The most likely explanation is the first. In 2 experiments in which radioactive iodide was injected, it was observed that the concentration was 2-3 times greater in the fetal serum than in the maternal serum. In one of the experiments it was not possible to demonstrate this.