Inner ring deiodination of thyroxine and 3,5,3'-triiodothyronine by human fetal membranes
Indirect evidence, based on injection of thyroxine (T4) into the amniotic cavity of humans, and maternal thyroidectomy in the rat, suggests that fetal membranes might be capable of converting T4 to 3,3',5'-triiodothyronine (rT3) by virtue of inner ring iodothyronine deiodinase activity. The present study was undertaken to provide direct evidence that human fetal membranes contain inner ring iodothyronine deiodinase activity directed toward T4 and 3,5,3'-triiodothyronine (T3). Homogenates of human fetal membranes were incubated with 125I-labeled T4, rT3, and T3, and with stable T4. Conversion of 125(I)-T4 to 125(I)-rT3 was noted in chorion and amnion. 125I-T3 was converted to 125(I)-3,3'-diiodothyronine (T2) in chorion and amnion. 125(I)-rT3 was stable in fetal membranes under the incubation conditions employed. Time-, temperature-, pH-, and protein content-dependent conversion of stable T4 to rT3 was found in fetal membranes. Iodothyronine metabolism did not occur in the absence of dithiothreitol. These studies indicate that human fetal membranes contain an inner ring deiodinase enzyme. Because of its intimate contact with the amniotic cavity, this enzyme may generate a portion of the rT3 found in amniotic fluid.
- Research Organization:
- Univ. of Massachusetts Medical School, Worcester
- OSTI ID:
- 6972641
- Journal Information:
- Am. J. Obstet. Gynecol.; (United States), Journal Name: Am. J. Obstet. Gynecol.; (United States) Vol. 147:7; ISSN AJOGA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400102* -- Chemical & Spectral Procedures
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
ENZYME ACTIVITY
FETUSES
HALOGENS
HORMONES
INTERMEDIATE MASS NUCLEI
IODINE
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
MEMBRANES
METABOLISM
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
PEPTIDE HORMONES
RADIOISOTOPES
REACTION KINETICS
THYROID HORMONES
THYROXINE
TRACER TECHNIQUES
TRIIODOTHYRONINE