Reverse triiodothyronine (3,3′,5′-triiodothyronine, reverse T
3, or rT
3) is an
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Is ...
of
triiodothyronine
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Production of T3 and its prohormone thyrox ...
(3,5,3′ triiodothyronine, T
3).
Reverse T
3 is the third-most common iodothyronine the thyroid gland releases into the bloodstream, at 0.9%;
tetraiodothyronine (levothyroxine, T
4) constitutes 90% and T
3 is 9%. However, 95% of rT
3 in human blood is made elsewhere in the body, as
enzymes
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
remove a particular
iodine
Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...
atom from T
4.
The production of hormone by the thyroid gland is controlled by the
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
and
pituitary gland
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The h ...
. The physiological activity of thyroid hormone is regulated by a system of enzymes that activate, inactivate or simply discard the prohormone T
4 and in turn functionally modify T
3 and rT
3. These enzymes operate under complex direction of systems including neurotransmitters, hormones, markers of metabolism and immunological signals.
The levels of rT
3 increase in conditions such as
euthyroid sick syndrome
Euthyroid sick syndrome (ESS) is a state of adaptation or dysregulation of thyrotropic feedback control wherein the levels of T3 and/or T4 are abnormal, but the thyroid gland does not appear to be dysfunctional. This condition may result from ...
because its clearance decreases while its production stays the same. The decreased clearance is possibly from lower
Thyroxine 5-deiodinase activity in the peripheral tissue or decreased liver uptake of rT
3.
In addition, increased rT
3 concentrations result from upregulated
Thyroxine 5-deiodinase activity in critical illness, starvation and fetal life.
Reactions
References
External links
*
{{Xenobiotic-sensing receptor modulators
Iodinated tyrosine derivatives
Thyroid