T4 in serum, Decreased leads to Decreased, Thyroxine (T4) in tissues

Thyroxine (T4) uptake from serum into tissues plays a substantial role in thyroid hormone action, as it can then be available for enzymatic conversion to the active hormone, triiodothyronine (T3). Uptake of T4 into cells/tissues is mediated by active transport proteins that exhibit unique expression profiles depending on tissue type and timing of development (Hennemann et al., 2001; Visser et al., 2011, 2007; Connors et al., 2010; Friesema et al., 2005). Specific regulation of transporter profiles plays a role in timing of thyroid hormone uptake into specific tissues for proper sequencing of development and protection against metabolism and clearance of thyroid hormone during critical developmental periods. Although several different classes of proteins have been identified as capable of transporting T4 (and T3) across plasma membranes, three proteins in particular have been shown to have high affinity and specificity toward thyroid hormone; namely, MCT8, MCT10 and OATP1c1 (Friesema et al., 2003, 2008; Pizzagalli et al., 2002; Jansen et al., 2007; Mayer et al., 2014). These transport proteins have primarily been studied in relation to mammalian brain development, so the details of their role in other species and tissues during vertebrate development are not well-understood.