Metabolism of Thiourea S35by the Fetal Thyroid of the Rat

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Abstract
The metabolism of thiourea S35 by the developing fetal rat was studied by measurement of the radioactivity in fluids and tissues, paper chromatographic analysis of the chemical state of the S35, and histologic localization of the S35 by radioautography. Rapid passage of the thiourea from the mother to the fetus occurred. In older embryos, at 12 and 24 hr after the administration of thiourea the amniotic fluid concentration was higher than that in the maternal serum. The fetal serum concentration was lower than that of the maternal serum. The fetal thyroid to fetal serum concentration ratio began increasing on the 17th day, and by the 20th day it was 9.3 as compared with 24 for the mother. The time of appearance of the concentrating ability for thiourea S35 coincides with that for I131. The S35 was predominantly present as thiourea in the serum, amniotic fluid and urine, but some protein-bound material was also found in liver tissues, serum and amniotic fluid. Both fetal and maternal thyroid tissue had increased amounts of S3S as either sulfate or thiosulfate. The radioautographs showed concentration of grains over thyroid cells and colloid at 3 hr, but after 12 and 24 hr most of the activity was over the colloid. Some concentration of S36 was observed in fetal tracheal cartilage and in the tubules of the maternal kidney.

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