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Transthyretin as a thyroid hormone carrier: function revisited.
1Life and Health Sciences Research Institute, Health Sciences School, University of Minho, Braga, Portugal. japalha@ecsaude.uminho.pt
Clinical Chemistry and Laboratory Medicine
|January 30, 2003
Summary
Thyroid hormones are crucial for development and metabolism. Studies show that major plasma transport proteins are not essential for thyroid hormone uptake or maintaining a healthy thyroid status.
Area of Science:
- Endocrinology
- Molecular Biology
- Physiology
Background:
- Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), regulate mammalian development and metabolism.
- Most circulating thyroid hormones are bound to plasma proteins like thyroxine-binding globulin, transthyretin, and albumin.
- The precise role of these binding proteins in hormone transport to target tissues has been debated.
Purpose of the Study:
- To investigate the necessity of major plasma transport proteins for thyroid hormone homeostasis.
- To determine if transthyretin is essential for thyroid hormone entry into the brain and other tissues.
Main Methods:
- Utilized transthyretin-null mice to assess thyroid hormone transport and tissue levels.
- Examined euthyroid status in humans lacking thyroxine-binding globulin and in rats lacking albumin.
Main Results:
- Transthyretin-null mice maintained normal thyroid hormone levels and tissue distribution.
- Humans without thyroxine-binding globulin and rats without albumin also exhibited normal euthyroid status.
- These findings indicate no strict dependence on major plasma carriers for thyroid hormone regulation.
Conclusions:
- Thyroid hormone homeostasis is not dependent on the presence of major plasma carrier proteins.
- The free hormone hypothesis, suggesting free circulating hormone is the active form, is supported by these findings.