Spatially Dependent Tissue Distribution of Thyroid Hormones by Plasma Thyroid Hormone Binding Proteins.

Thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin (ALB) are plasma thyroid hormone (TH) binding proteins (THBPs) that carry THs from the thyroid gland to extrathyroidal tissues.The respective roles of the 3 THBP species in unloading THs once arriving at a tissue are not completely understood.Here we developed a spatial human kinetic model of THs and showed that the three THBPs may unload comparable amounts of thyroxine (T4) in the liver but TBG is dominant in contributing T4 in tissues slowly perfused by blood as well as in contributing triiodothyronine (T3) regardless of the tissue's perfusion rate.The TH amounts unloaded by each THBP species are spatially dependent and nonlinear, with ALB being the dominant contributor near the arterial end but conceding to TBG near the venous end in a tissue.Our model provides novel insights into the differential roles of THBPs in local TH tissue distribution.