Endocrine Abstracts

Both action and metabolism of thyroid hormone are intracellular events which require the transport of iodothyronines across the plasma membrane. This does not occur by simple diffusion but is facilitated by transport proteins. During the last few years thyroid hormone transporters have been characterized at the molecular level. These include the Na+-taurocholate cotransporting polypeptide (NTCP), different members of the Na+-independent organic anion tran...

So far it has been assumed that thyroid hormones -due to their lipophilicity- enter their target cells just by slipping through the membrane. After the initial description of a specific transport molecule for thyroid hormone in 2003 (Friesema et al. JBC) a new paradigm of thyroid hormone physiology has emerged. It turns out that as everything in nature, also the entering of thyroid hormone in its target cell is well regulated and the gate keeper is the MCT8 transporter, at lea...

In rodents synthetic glucocorticoids such as e.g. dexamethasone poorly penetrate the blood brain barrier because of multidrug resistance P-glycoprotein (mdr-Pgp). Also cortisol, not naturally occurring in rats and mice, is hampered in uptake. The evidence for this role of the efflux transporter was substantiated with the mdr1a knock out mice. 3H- cortisol and 3H-dexamethasone administered to the mdr1a mutants did label brain targets that retained the ster...

Experimental data demonstrate interactions of steroids with efflux carriers of the multidrug-resistance transporter family (P-glycoprotein, MRP) as well as the poly-specific uptake carriers of the organic anion transporting polypetptide (OATP), organic cation transporter (OCT), and the organic anion transporter (OAT) families in different tissues.P-glycoprotein is associated with glucocorticoid-resistance of many diseases including cancer but also modula...