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Maturation of hepatic desulfation activity in developing rats
1Department of Nuclear Medicine, Tri-Service General Hospital, Taipei, Taiwan ROC.
Summary
Thyroid hormone metabolism in developing rats shows low desulfation activity in fetuses, with activity significantly increasing after birth. This maturation, driven by enzyme capacity, is complete by two months of age.
Area of Science:
- Endocrinology
- Developmental Biology
- Biochemistry
Background:
- High levels of 3,3',5-triiodothyronine sulfate (T3S) and low 3,3',5-triiodothyronine (T3) are observed in fetal rat serum.
- The T3S/T3 ratio is reversed in maternal circulation, with higher desulfation activity in maternal rats compared to fetuses.
Purpose of the Study:
- To characterize the maturation of desulfation activity in developing rats.
- To investigate the role of hepatic microsomes in the desulfation of T3S to T3 during development.
Main Methods:
- Incubation of liver microsomes from fetal and maternal rats with T3S as a substrate.
- Measurement of desulfated T3 using radioimmunoassay.
- Comparison of Km and Vmax values for T3S desulfation across different age groups.
Main Results:
- Hepatic microsomal preparations from fetal rats exhibited minimal desulfation activity compared to newborns.
- A significant increase in desulfation activity was observed between 1 and 2 months of age.
- Vmax values for T3S desulfation increased progressively after birth, reaching maternal levels by 2 months, while Km values remained consistent.
Conclusions:
- Rat liver microsomal desulfation activity matures by 2 months of age, primarily due to increased enzyme capacity.
- The sulfation-desulfation of T3 may be crucial for thyroid hormone regulation in developing mammals.