Thyroid Hormone Serum Transport Proteins

Thyroid hormone (TH) effects are dependent on the quantity of the hormone that reaches the tissues, hormone activation and the availability of unaltered TH receptors in the cells nuclei and cytoplasm. Since TH enters the cell unbound, the concentration of free rather than total hormone reflects more accurately the activity level of TH-dependent processes. Under normal conditions, changes in free hormone level are adjusted by appropriate stimulation or suppression of hormone secretion and disposal. Total TH concentration in serum is normally kept at a level proportional to the concentration of carrier proteins, and appropriate to maintain a constant free hormone level.