Normal Cellular Uptake of Thyroxine (T4) from Serum of Patients with Familial Dysalbuminemic Hyperthyroxinemia (FDH) or Elevated Thyroxine-Binding Globulin (TBG): T4 Bound to Albumin is not Preferentially Transferred to Tissue
Only free thyroid hormone is thought to enter cells and be metabolically active while protein bound thyroid hormone, in equilibrium with the free fraction, remains in the intravascular compartment (1). Evidence that albumin-bound T4 preferentially enters hepatocytes (2) and that subjects with FDH have increased hepatic T4 delivery (3) have challenged this concept. We examined the in vitro cellular uptake of T4 by human hepatocytes, Hep G2 (4), from serum of subjects with FDH. Results were compared to those from sera matched to the FDH sera by total T4 concentrations and obtained from individuals with high TBG or thyrotoxicosis.
KeywordsThyroid Hormone Cellular Uptake Human Hepatocyte Free Fraction Equilibrium Dialysis
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