The kinetics of thyroid hormone transporters and their role in non-thyroidal illness and starvation.

Kinetic tracer studies show that thyroid hormones are transported into target tissues by stereospecific, high-affinity, low-capacity transporters, both in animals and humans. The K(d) of binding to the transporter varies within the nanomolar range. The different thyroid hormones (T(4), T(3), and rT(3)) are transported via different transporters, except in the pituitary, where they share the same transporter.

Notes on the history of cellular uptake and deiodination of thyroid hormone.

In this mini review on the history of the research devoted to thyroid hormone metabolism two pathways are discussed, i.e. uptake and subsequent deiodination in cells and tissues.

Thyroxine plus low-dose, slow-release triiodothyronine replacement in hypothyroidism: proof of principle.

Studies in hypothyroid rats show that, when infused with a combination of thyroxine (T4) plus triiodothyronine (T3) to normalize thyrotropin (TSH), euthyroidism in all organs is only ensured when T(4) and T(3) are administered in a ratio as normally secreted by the rat thyroid. As substitution with T(4)-only results in an abnormal serum T(4)/T(3) ratio, it is also possible that in humans, euthyroidism does not exist at the tissue level in many organs, considering that iodothyronine metabolism in the human and the rat share many similar mechanisms. Recent reports in which cognitive function and well-being are compared in patients with primary hypothyroidism substituted with T(4)-only versus substitution with T(4) plus T(3) result in controversial findings in that either positive or no effects were found.

Effects of thyroid state on the expression of hepatic thyroid hormone transporters in rats.

Liver uptake of thyroxine (T4) is mediated by transporters and is rate limiting for hepatic 3,3',5-triiodothyronine (T3) production. We investigated whether hepatic mRNA for T4 transporters is regulated by thyroid state using Xenopus laevis oocytes as an expression system. Because X.